diff --git a/tests/php/TestCase.php b/tests/php/TestCase.php
index b8f036d..19e2463 100644
--- a/tests/php/TestCase.php
+++ b/tests/php/TestCase.php
@@ -81,5 +81,68 @@ protected function checkRequirements(): void { // phpcs:ignore Generic.CodeAnaly
 		parent::checkRequirements();
 	}
 
+	/**
+	 * Intercept Algolia SDK HTTP calls and collect request paths.
+	 *
+	 * @param array<int, string>              $recorded_paths Paths captured from outgoing SDK requests.
+	 * @param (callable(string): string)|null $body_for_path Optional callback to provide a response body for a given request path.
+	 * @param string|null                     $throw_on_path_segment Optional path segment that triggers a RuntimeException when matched.
+	 */
+	public function mock_algolia_http_client( array &$recorded_paths, ?callable $body_for_path = null, ?string $throw_on_path_segment = null ): void {
+		\OneSearch\Vendor\Algolia\AlgoliaSearch\Algolia::setHttpClient(
+			new class( $recorded_paths, $body_for_path, $throw_on_path_segment ) implements \OneSearch\Vendor\Algolia\AlgoliaSearch\Http\HttpClientInterface {
+				/** @var array<int, string> */
+				private array $paths;
+
+				/** @var (callable(string): string)|null */
+				private $body_for_path;
+
+				/** @var string|null */
+				private ?string $throw_on_path_segment;
+
+				/**
+				 * @param array<int, string>              $paths Reference to the array that records intercepted request paths.
+				 * @param (callable(string): string)|null $body_for_path Optional callback to generate mock response bodies.
+				 * @param string|null                     $throw_on_path_segment Optional path segment that triggers a RuntimeException when matched.
+				 */
+				public function __construct( array &$paths, ?callable $body_for_path, ?string $throw_on_path_segment ) {
+					$this->paths                 = &$paths;
+					$this->body_for_path         = $body_for_path;
+					$this->throw_on_path_segment = $throw_on_path_segment;
+				}
+
+				/**
+				 * {@inheritDoc}
+				 *
+				 * @param \OneSearch\Vendor\Psr\Http\Message\RequestInterface $request         The PSR-7 request.
+				 * @param mixed                                               $timeout         Request timeout.
+				 * @param mixed                                               $connect_timeout Connection timeout.
+				 * @throws \RuntimeException When the configured path segment is encountered.
+				 */
+				public function sendRequest( \OneSearch\Vendor\Psr\Http\Message\RequestInterface $request, mixed $timeout, mixed $connect_timeout ): \OneSearch\Vendor\Psr\Http\Message\ResponseInterface { // phpcs:ignore SlevomatCodingStandard.Functions.UnusedParameter.UnusedParameter
+					$path          = (string) $request->getUri()->getPath();
+					$this->paths[] = $path;
+
+					if ( null !== $this->throw_on_path_segment && str_contains( $path, $this->throw_on_path_segment ) ) {
+						throw new \RuntimeException( 'forced test exception' );
+					}
+
+					if ( null !== $this->body_for_path ) {
+						$body = (string) call_user_func( $this->body_for_path, $path );
+					} elseif ( str_contains( $path, '/task/' ) ) {
+						$body = '{"status":"published","pendingTask":false}';
+					} elseif ( str_contains( $path, '/query' ) ) {
+						$body = '{"hits":[{"objectID":"1"}],"nbHits":1,"page":0,"hitsPerPage":20}';
+					} else {
+						$body = '{"taskID":1,"updatedAt":"2024-01-01T00:00:00.000Z"}';
+					}
+
+					// @phpstan-ignore return.type
+					return new \OneSearch\Vendor\Algolia\AlgoliaSearch\Http\Psr7\Response( 200, [], $body );
+				}
+			}
+		);
+	}
+
 	// Add any common setup or utility methods for tests here.
 }
diff --git a/tests/php/Unit/Modules/Search/IndexTest.php b/tests/php/Unit/Modules/Search/IndexTest.php
new file mode 100644
index 0000000..5a0a263
--- /dev/null
+++ b/tests/php/Unit/Modules/Search/IndexTest.php
@@ -0,0 +1,347 @@
+<?php
+/**
+ * Index unit tests.
+ *
+ * @package OneSearch\Tests\Unit\Modules\Search
+ */
+
+declare(strict_types = 1);
+
+namespace OneSearch\Tests\Unit\Modules\Search;
+
+use OneSearch\Modules\Rest\Governing_Data_Handler;
+use OneSearch\Modules\Search\Index;
+use OneSearch\Modules\Search\Settings as Search_Settings;
+use OneSearch\Modules\Settings\Settings;
+use OneSearch\Tests\TestCase;
+use OneSearch\Vendor\Algolia\AlgoliaSearch\Algolia as AlgoliaSDK;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+/**
+ * Tests for the Index class.
+ */
+#[CoversClass( \OneSearch\Modules\Search\Index::class )]
+final class IndexTest extends TestCase {
+	/**
+	 * {@inheritDoc}
+	 */
+	protected function tearDown(): void {
+		AlgoliaSDK::resetHttpClient();
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Returns WP_Error when Algolia credentials are missing.
+	 */
+	public function test_get_index_returns_error_without_credentials(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$index  = new Index();
+		$result = $index->get_index();
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+		$this->assertSame( 'Algolia admin credentials missing.', $result->get_error_message() );
+	}
+
+	/**
+	 * Returns SearchIndex when credentials are valid.
+	 */
+	public function test_get_index_returns_search_index_with_valid_credentials(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$index  = new Index();
+		$result = $index->get_index();
+
+		$this->assertInstanceOf( \OneSearch\Vendor\Algolia\AlgoliaSearch\SearchIndex::class, $result );
+	}
+
+	/**
+	 * Caches the index instance on subsequent calls.
+	 */
+	public function test_get_index_returns_same_instance_on_second_call(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$index  = new Index();
+		$first  = $index->get_index();
+		$second = $index->get_index();
+
+		$this->assertSame( $first, $second );
+	}
+
+	/**
+	 * Returns WP_Error when credentials are missing.
+	 */
+	public function test_delete_index_returns_error_without_credentials(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$result = ( new Index() )->delete_index();
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns true for delete_index with valid credentials on governing sites.
+	 */
+	public function test_delete_index_returns_true_with_valid_credentials(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->delete_index();
+
+		$this->assertTrue( $result );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Returns true for delete_index with valid credentials on consumer site.
+	 */
+	public function test_delete_index_returns_true_with_valid_credentials_on_consumer(): void {
+		$this->set_credentials( Settings::SITE_TYPE_CONSUMER );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->delete_index();
+
+		$this->assertTrue( $result );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Returns WP_Error when credentials are missing.
+	 */
+	public function test_delete_by_returns_error_without_credentials(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$result = ( new Index() )->delete_by( [ 'filters' => 'site_url:"http://test.com"' ] );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns true for delete_by with valid credentials.
+	 */
+	public function test_delete_by_returns_true_with_valid_credentials(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->delete_by( [ 'filters' => 'site_url:"http://test.com"' ] );
+
+		$this->assertTrue( $result );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Returns WP_Error when SDK throws during delete_by failure.
+	 */
+	public function test_delete_by_returns_error_when_sdk_throws(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths, null, '/deleteBy' );
+
+		$result = ( new Index() )->delete_by( [ 'filters' => 'site_url:"http://test.com"' ] );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'onesearch_algolia_delete_by_failed', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns WP_Error when credentials are missing.
+	 */
+	public function test_save_records_returns_error_without_credentials(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$result = ( new Index() )->save_records( [] );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns true for save_records with valid credentials.
+	 */
+	public function test_save_records_returns_true_with_valid_credentials(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->save_records(
+			[
+				[
+					'objectID'   => '1',
+					'post_title' => 'Test',
+				],
+			]
+		);
+
+		$this->assertTrue( $result );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Returns WP_Error when SDK throws during save_records.
+	 */
+	public function test_save_records_returns_error_when_sdk_throws(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths, null, '/batch' );
+
+		$result = ( new Index() )->save_records(
+			[
+				[
+					'objectID'   => '1',
+					'post_title' => 'Test',
+				],
+			]
+		);
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'onesearch_algolia_save_records_failed', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns WP_Error when credentials are missing.
+	 */
+	public function test_search_returns_error_without_credentials(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$result = ( new Index() )->search( 'test query' );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns search payload for search with valid credentials.
+	 */
+	public function test_search_returns_results_with_valid_credentials(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->search( 'test query' );
+
+		$this->assertIsArray( $result );
+		$this->assertArrayHasKey( 'hits', $result );
+		$this->assertSame( '1', $result['hits'][0]['objectID'] ?? '' );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Returns WP_Error when SDK throws during search.
+	 */
+	public function test_search_returns_error_when_sdk_throws(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths, null, '/query' );
+
+		$result = ( new Index() )->search( 'test query' );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'onesearch_algolia_search_failed', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns WP_Error when SDK throws while setting index settings.
+	 */
+	public function test_delete_by_returns_set_settings_error_when_sdk_throws_on_settings(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths, null, '/settings' );
+
+		$result = ( new Index() )->delete_by( [ 'filters' => 'site_url:"http://test.com"' ] );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_set_settings_failed', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns WP_Error when delete_by fails (no credentials).
+	 */
+	public function test_index_all_posts_returns_error_when_delete_fails(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$result = ( new Index() )->index_all_posts( [ 'post' ] );
+
+		$this->assertWPError( $result );
+		$this->assertSame( 'algolia_credentials_missing', $result->get_error_code() );
+	}
+
+	/**
+	 * Returns true when index_all_posts is called with no post types and valid credentials.
+	 */
+	public function test_index_all_posts_returns_true_with_valid_credentials_and_no_post_types(): void {
+		$this->set_credentials( Settings::SITE_TYPE_GOVERNING );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$result = ( new Index() )->index_all_posts( [] );
+
+		$this->assertTrue( $result );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Set site context with valid Algolia credentials.
+	 *
+	 * @param string $site_type Site type (governing or consumer).
+	 */
+	private function set_credentials( string $site_type ): void {
+
+		if ( Settings::SITE_TYPE_GOVERNING === $site_type ) {
+			update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+			Search_Settings::set_algolia_credentials(
+				[
+					'app_id'    => 'TEST_APP',
+					'write_key' => 'TEST_KEY',
+				]
+			);
+		}
+		if ( Settings::SITE_TYPE_CONSUMER === $site_type ) {
+			update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+			Settings::set_parent_site_url( 'https://governing.example.com' );
+
+			// Pre-populate the brand-config cache so Algolia::get_algolia_credentials()
+			// on a consumer site resolves locally instead of making an HTTP request
+			// to the governing site.
+			set_transient(
+				Governing_Data_Handler::TRANSIENT_KEY,
+				[
+					'algolia_credentials' => [
+						'app_id'    => 'TEST_APP',
+						'write_key' => 'TEST_KEY',
+					],
+					'search_settings'     => [
+						'algolia_enabled'  => true,
+						'searchable_sites' => [],
+					],
+					'indexable_entities'  => [],
+					'available_sites'     => [],
+				],
+				HOUR_IN_SECONDS
+			);
+		}
+	}
+}
diff --git a/tests/php/Unit/Modules/Search/SearchTest.php b/tests/php/Unit/Modules/Search/SearchTest.php
new file mode 100644
index 0000000..ab2e6f5
--- /dev/null
+++ b/tests/php/Unit/Modules/Search/SearchTest.php
@@ -0,0 +1,716 @@
+<?php
+/**
+ * Search integration unit tests.
+ *
+ * @package OneSearch\Tests\Unit\Modules\Search
+ */
+
+declare(strict_types = 1);
+
+namespace OneSearch\Tests\Unit\Modules\Search;
+
+use OneSearch\Modules\Search\Search;
+use OneSearch\Modules\Search\Settings as Search_Settings;
+use OneSearch\Modules\Settings\Settings;
+use OneSearch\Tests\TestCase;
+use OneSearch\Utils;
+use OneSearch\Vendor\Algolia\AlgoliaSearch\Algolia as AlgoliaSDK;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+/**
+ * Tests for the Search class.
+ */
+#[CoversClass( \OneSearch\Modules\Search\Search::class )]
+final class SearchTest extends TestCase {
+	/**
+	 * {@inheritDoc}
+	 */
+	protected function tearDown(): void {
+		AlgoliaSDK::resetHttpClient();
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Ensures class can be instantiated.
+	 */
+	public function test_class_instantiation(): void {
+		$search = new Search();
+		$search->register_hooks();
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Returns original posts when search is not enabled.
+	 */
+	public function test_get_algolia_results_returns_original_posts_when_search_disabled(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+		delete_option( Settings::OPTION_SITE_TYPE );
+
+		$search   = new Search();
+		$query    = new \WP_Query();
+		$original = [ self::factory()->post->create_and_get() ];
+
+		$result = $search->get_algolia_results( $original, $query );
+
+		$this->assertSame( $original, $result );
+	}
+
+	/**
+	 * Returns original posts when query is not a search query.
+	 */
+	public function test_get_algolia_results_returns_original_posts_for_non_search_query(): void {
+		$this->enable_search_for_governing_site();
+
+		$search = new Search();
+		$query  = new \WP_Query();
+		$query->init();
+
+		$original = [ self::factory()->post->create_and_get() ];
+		$result   = $search->get_algolia_results( $original, $query );
+
+		$this->assertSame( $original, $result );
+	}
+
+	/**
+	 * Returns original posts when the query is not a WP_Query instance.
+	 */
+	public function test_get_algolia_results_returns_original_posts_for_non_wp_query(): void {
+		$search   = new Search();
+		$original = [ self::factory()->post->create_and_get() ];
+
+		// @phpstan-ignore argument.type
+		$result = $search->get_algolia_results( $original, 'not-a-query' );
+
+		$this->assertSame( $original, $result );
+	}
+
+	/**
+	 * Returns mapped remote posts when search is enabled and query is a main search query.
+	 */
+	public function test_get_algolia_results_returns_remote_posts_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		Search_Settings::set_algolia_credentials(
+			[
+				'app_id'    => 'TEST_APP',
+				'write_key' => 'TEST_KEY',
+			]
+		);
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client(
+			$recorded_paths,
+			static function ( string $path ): string {
+				if ( str_contains( $path, '/query' ) ) {
+					return wp_json_encode(
+						[
+							'hits'        => [
+								[
+									'objectID'          => '17',
+									'site_post_id'      => '17',
+									'post_id'           => 17,
+									'post_title'        => 'Remote Post',
+									'post_type'         => 'post',
+									'permalink'         => 'https://remote.example.com/posts/17/',
+									'site_url'          => 'https://remote.example.com/',
+									'site_name'         => 'Remote',
+									'total_chunks'      => 1,
+									'post_date_gmt'     => 1710000000,
+									'post_modified_gmt' => 1710000000,
+								],
+							],
+							'nbHits'      => 1,
+							'page'        => 0,
+							'hitsPerPage' => 10,
+						]
+					) ?: '{}';
+				}
+
+				if ( str_contains( $path, '/task/' ) ) {
+					return '{"status":"published","pendingTask":false}';
+				}
+
+				return '{"taskID":1,"updatedAt":"2024-01-01T00:00:00.000Z"}';
+			}
+		);
+
+		$this->prime_main_search_query( 'remote test' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Reading query prepared by helper.
+		global $wp_query;
+
+		$search = new Search();
+		$result = $search->get_algolia_results( [], $wp_query );
+
+		$this->assertNotEmpty( $result );
+		$this->assertInstanceOf( \WP_Post::class, $result[0] );
+		$this->assertSame( -18, $result[0]->ID );
+		$this->assertSame( 'https://remote.example.com/posts/17/', $result[0]->guid );
+		$this->assertSame( 1, $wp_query->post_count );
+		$this->assertSame( 1, $wp_query->found_posts );
+		$this->assertTrue( (bool) ( $wp_query->is_algolia_search ?? false ) );
+		$this->assertNotEmpty( $recorded_paths );
+	}
+
+	/**
+	 * Sorts hits by Algolia ranking score (descending) without raising notices.
+	 */
+	public function test_get_algolia_results_sorts_hits_by_ranking_score(): void {
+		$this->enable_search_for_governing_site();
+		Search_Settings::set_algolia_credentials(
+			[
+				'app_id'    => 'TEST_APP',
+				'write_key' => 'TEST_KEY',
+			]
+		);
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client(
+			$recorded_paths,
+			static function ( string $path ): string {
+				if ( str_contains( $path, '/query' ) ) {
+					return wp_json_encode(
+						[
+							'hits'        => [
+								[
+									'objectID'          => '20',
+									'site_post_id'      => '20',
+									'post_id'           => 20,
+									'post_title'        => 'Middle Score',
+									'post_type'         => 'post',
+									'permalink'         => 'https://remote.example.com/posts/20/',
+									'site_url'          => 'https://remote.example.com/',
+									'site_name'         => 'Remote',
+									'total_chunks'      => 1,
+									'post_date_gmt'     => 1710000000,
+									'post_modified_gmt' => 1710000000,
+									'_rankingInfo'      => [ 'rankingScore' => 0.5 ],
+								],
+								[
+									'objectID'          => '30',
+									'site_post_id'      => '30',
+									'post_id'           => 30,
+									'post_title'        => 'Lowest Score',
+									'post_type'         => 'post',
+									'permalink'         => 'https://remote.example.com/posts/30/',
+									'site_url'          => 'https://remote.example.com/',
+									'site_name'         => 'Remote',
+									'total_chunks'      => 1,
+									'post_date_gmt'     => 1710000000,
+									'post_modified_gmt' => 1710000000,
+									'_rankingInfo'      => [ 'rankingScore' => 0.1 ],
+								],
+								[
+									'objectID'          => '40',
+									'site_post_id'      => '40',
+									'post_id'           => 40,
+									'post_title'        => 'Highest Score',
+									'post_type'         => 'post',
+									'permalink'         => 'https://remote.example.com/posts/40/',
+									'site_url'          => 'https://remote.example.com/',
+									'site_name'         => 'Remote',
+									'total_chunks'      => 1,
+									'post_date_gmt'     => 1710000000,
+									'post_modified_gmt' => 1710000000,
+									'_rankingInfo'      => [ 'rankingScore' => 0.9 ],
+								],
+							],
+							'nbHits'      => 3,
+							'page'        => 0,
+							'hitsPerPage' => 10,
+						]
+					) ?: '{}';
+				}
+
+				if ( str_contains( $path, '/task/' ) ) {
+					return '{"status":"published","pendingTask":false}';
+				}
+
+				return '{"taskID":1,"updatedAt":"2024-01-01T00:00:00.000Z"}';
+			}
+		);
+
+		$this->prime_main_search_query( 'remote test' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Reading query prepared by helper.
+		global $wp_query;
+
+		$search = new Search();
+		$result = $search->get_algolia_results( [], $wp_query );
+
+		$this->assertCount( 3, $result );
+		$this->assertSame( 'Highest Score', $result[0]->post_title );
+		$this->assertSame( 'Middle Score', $result[1]->post_title );
+		$this->assertSame( 'Lowest Score', $result[2]->post_title );
+	}
+
+	/**
+	 * Returns default permalink for local posts (positive ID).
+	 */
+	public function test_get_post_type_permalink_returns_default_for_local_post(): void {
+		$search = new Search();
+		$post   = self::factory()->post->create_and_get();
+
+		$result = $search->get_post_type_permalink( 'https://example.com/test/', $post );
+
+		$this->assertSame( 'https://example.com/test/', $result );
+	}
+
+	/**
+	 * Returns remote permalink for placeholder posts during enabled search.
+	 */
+	public function test_get_post_type_permalink_returns_remote_for_placeholder_post(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		global $wp_query; // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+
+		$remote_post                        = new \WP_Post( new \stdClass() );
+		$remote_post->onesearch_original_id = 17;
+		$remote_post->guid                  = 'https://remote.example.com/posts/17/';
+
+		$wp_query->posts = [ $remote_post ];
+
+		$search = new Search();
+		$result = $search->get_post_type_permalink( 'https://example.com/local/', -18 );
+
+		$this->assertSame( 'https://remote.example.com/posts/17/', $result );
+	}
+
+	/**
+	 * Returns default author name when search is not enabled.
+	 *
+	 * Primes $wp_query and sets a remote $post so that should_filter_query() and
+	 * the negative-ID guard both pass — ensuring the default is returned solely
+	 * because search is disabled, not because of a missing query or local post.
+	 */
+	public function test_get_post_author_returns_default_when_search_disabled(): void {
+		// Set up everything search needs EXCEPT the search settings option itself.
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post     = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID = -99;
+		$post->onesearch_remote_post_author_display_name = 'Remote Author';
+
+		// Now disable search — this is the sole reason the default should be returned.
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_post_author( 'Default Author' );
+
+		$this->assertSame( 'Default Author', $result );
+	}
+
+	/**
+	 * Returns remote author name when search is enabled for remote posts.
+	 */
+	public function test_get_post_author_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post     = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID = -10;
+		$post->onesearch_remote_post_author_display_name = 'Remote Author';
+
+		$search = new Search();
+		$result = $search->get_post_author( 'Default Author' );
+
+		$this->assertSame( 'Remote Author', $result );
+	}
+
+	/**
+	 * Returns default author link when search is not enabled.
+	 *
+	 * Primes query and remote $post so the only exit condition is search being disabled.
+	 */
+	public function test_get_post_author_link_returns_default_when_search_disabled(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                                    = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                                = -99;
+		$post->onesearch_remote_post_author_link = 'https://remote.example.com/authors/john/';
+
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_post_author_link( 'https://example.com/author/admin/' );
+
+		$this->assertSame( 'https://example.com/author/admin/', $result );
+	}
+
+	/**
+	 * Returns remote author link when search is enabled for remote posts.
+	 */
+	public function test_get_post_author_link_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                                    = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                                = -11;
+		$post->onesearch_remote_post_author_link = 'https://remote.example.com/authors/john/';
+
+		$search = new Search();
+		$result = $search->get_post_author_link( 'https://example.com/author/admin/' );
+
+		$this->assertSame( 'https://remote.example.com/authors/john/', $result );
+	}
+
+	/**
+	 * Returns default avatar URL when search is not enabled.
+	 *
+	 * Primes query and remote $post so the only exit condition is search being disabled.
+	 */
+	public function test_get_post_author_avatar_returns_default_when_search_disabled(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                                        = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                                    = -99;
+		$post->onesearch_remote_post_author_gravatar = 'https://remote.example.com/avatar.jpg';
+
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_post_author_avatar( 'https://example.com/avatar.jpg' );
+
+		$this->assertSame( 'https://example.com/avatar.jpg', $result );
+	}
+
+	/**
+	 * Returns remote author avatar when search is enabled for remote posts.
+	 */
+	public function test_get_post_author_avatar_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                                        = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                                    = -12;
+		$post->onesearch_remote_post_author_gravatar = 'https://remote.example.com/avatar.jpg';
+
+		$search = new Search();
+		$result = $search->get_post_author_avatar( 'https://example.com/avatar.jpg' );
+
+		$this->assertSame( 'https://remote.example.com/avatar.jpg', $result );
+	}
+
+	/**
+	 * Returns default term link when search is not enabled.
+	 *
+	 * Primes query and remote $post so the only exit condition is search being disabled.
+	 */
+	public function test_get_term_link_returns_default_when_search_disabled(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                              = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                          = -99;
+		$post->onesearch_remote_taxonomies = [
+			[
+				'taxonomy'  => 'category',
+				'term_id'   => 7,
+				'slug'      => 'news',
+				'term_link' => 'https://remote.example.com/category/news/',
+			],
+		];
+
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_term_link( 'https://example.com/category/news/', 7, 'category' );
+
+		$this->assertSame( 'https://example.com/category/news/', $result );
+	}
+
+	/**
+	 * Returns remote term link when search is enabled and taxonomy data exists.
+	 */
+	public function test_get_term_link_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                              = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                          = -13;
+		$post->onesearch_remote_taxonomies = [
+			[
+				'taxonomy'  => 'category',
+				'term_id'   => 7,
+				'slug'      => 'news',
+				'term_link' => 'https://remote.example.com/category/news/',
+			],
+		];
+
+		$search = new Search();
+		$result = $search->get_term_link( 'https://example.com/category/news/', 7, 'category' );
+
+		$this->assertSame( 'https://remote.example.com/category/news/', $result );
+	}
+
+	/**
+	 * Delegates to get_term_link with 'category' taxonomy.
+	 */
+	public function test_get_category_link_returns_default_when_search_disabled(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_category_link( 'https://example.com/category/tech/', 5 );
+
+		$this->assertSame( 'https://example.com/category/tech/', $result );
+	}
+
+	/**
+	 * Delegates to get_term_link with 'category' taxonomy for enabled remote search.
+	 */
+	public function test_get_category_link_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                              = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                          = -105;
+		$post->onesearch_remote_taxonomies = [
+			[
+				'taxonomy'  => 'category',
+				'term_id'   => 5,
+				'slug'      => 'tech',
+				'term_link' => 'https://remote.example.com/category/tech/',
+			],
+		];
+
+		$search = new Search();
+		$result = $search->get_category_link( 'https://example.com/category/tech/', 5 );
+
+		$this->assertSame( 'https://remote.example.com/category/tech/', $result );
+	}
+
+	/**
+	 * Delegates to get_term_link with 'post_tag' taxonomy.
+	 */
+	public function test_get_tag_link_returns_default_when_search_disabled(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search = new Search();
+		$result = $search->get_tag_link( 'https://example.com/tag/php/', 3 );
+
+		$this->assertSame( 'https://example.com/tag/php/', $result );
+	}
+
+	/**
+	 * Delegates to get_term_link with 'post_tag' taxonomy for enabled remote search.
+	 */
+	public function test_get_tag_link_returns_remote_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post                              = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID                          = -106;
+		$post->onesearch_remote_taxonomies = [
+			[
+				'taxonomy'  => 'post_tag',
+				'term_id'   => 3,
+				'slug'      => 'php',
+				'term_link' => 'https://remote.example.com/tag/php/',
+			],
+		];
+
+		$search = new Search();
+		$result = $search->get_tag_link( 'https://example.com/tag/php/', 3 );
+
+		$this->assertSame( 'https://remote.example.com/tag/php/', $result );
+	}
+
+	/**
+	 * Returns original terms when search is not enabled.
+	 */
+	public function test_get_post_terms_returns_original_when_search_disabled(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search   = new Search();
+		$original = [ new \WP_Term( new \stdClass() ) ];
+
+		$result = $search->get_post_terms( $original, 1, 'category' );
+		$this->assertSame( $original, $result );
+	}
+
+	/**
+	 * Returns mapped terms for enabled search when remote taxonomy metadata exists.
+	 */
+	public function test_get_post_terms_returns_remote_terms_when_search_enabled(): void {
+		$this->enable_search_for_governing_site();
+		$this->prime_main_search_query( 'test query' );
+
+		$post_id = self::factory()->post->create();
+		$post    = get_post( $post_id );
+
+		$this->assertInstanceOf( \WP_Post::class, $post );
+
+		$post->onesearch_remote_taxonomies = [
+			[
+				'taxonomy'    => 'category',
+				'term_id'     => 22,
+				'slug'        => 'remote-news',
+				'name'        => 'Remote News',
+				'term_link'   => 'https://remote.example.com/category/remote-news/',
+				'count'       => 3,
+				'description' => 'Remote category',
+				'parent'      => 0,
+			],
+		];
+
+		wp_cache_set( $post_id, $post, 'posts' );
+
+		$search = new Search();
+		$result = $search->get_post_terms( [], $post_id, 'category' );
+
+		$this->assertIsArray( $result );
+		$this->assertCount( 1, $result );
+		$this->assertInstanceOf( \WP_Term::class, $result[0] );
+		$this->assertSame( 'Remote News', $result[0]->name );
+		$this->assertSame( 'category', $result[0]->taxonomy );
+		$this->assertSame( 22, $result[0]->term_id );
+	}
+
+	/**
+	 * Returns unchanged block content when search is not enabled.
+	 *
+	 * Sets a negative-ID $post with a guid so the only exit condition is
+	 * search being disabled, not a missing/local post.
+	 */
+	public function test_filter_render_block_returns_original_when_search_disabled(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post       = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID   = -99;
+		$post->guid = 'https://remote.example.com/post/99/';
+
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$search  = new Search();
+		$content = '<h2><a href="https://example.com/old/">Title</a></h2>';
+		$block   = [ 'blockName' => 'core/post-title' ];
+
+		$result = $search->filter_render_block( $content, $block );
+
+		$this->assertSame( $content, $result );
+	}
+
+	/**
+	 * Rewrites title block link for remote posts when search is enabled.
+	 */
+	public function test_filter_render_block_rewrites_title_link_for_remote_post(): void {
+		$this->enable_search_for_governing_site();
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post       = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID   = -14;
+		$post->guid = 'https://remote.example.com/post/14/';
+
+		$search  = new Search();
+		$content = '<h2><a href="https://example.com/old/">Title</a></h2>';
+		$block   = [ 'blockName' => 'core/post-title' ];
+
+		$result = $search->filter_render_block( $content, $block );
+
+		$this->assertStringContainsString( 'https://remote.example.com/post/14/', $result );
+		$this->assertStringNotContainsString( 'https://example.com/old/', $result );
+	}
+
+	/**
+	 * Rewrites excerpt block text for remote posts when search is enabled.
+	 */
+	public function test_filter_render_block_rewrites_excerpt_for_remote_post(): void {
+		$this->enable_search_for_governing_site();
+
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited -- Setting up test global state.
+		global $post;
+
+		$post               = new \WP_Post( new \stdClass() ); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$post->ID           = -15;
+		$post->guid         = 'https://remote.example.com/post/15/';
+		$post->post_excerpt = 'Remote excerpt body';
+
+		$search  = new Search();
+		$content = '<div class="wp-block-post-excerpt"><p>Old excerpt</p></div>';
+		$block   = [ 'blockName' => 'core/post-excerpt' ];
+
+		$result = $search->filter_render_block( $content, $block );
+
+		$this->assertStringContainsString( 'Remote excerpt body', $result );
+		$this->assertStringNotContainsString( 'Old excerpt', $result );
+	}
+
+	/**
+	 * Enables Algolia for the governing site in options.
+	 */
+	private function enable_search_for_governing_site(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		$site_url               = Utils::normalize_url( get_site_url() );
+		$site_url_with_trailing = trailingslashit( get_site_url() );
+		update_option(
+			Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS,
+			[
+				$site_url               => [
+					'algolia_enabled'  => true,
+					'searchable_sites' => [ $site_url ],
+				],
+				$site_url_with_trailing => [
+					'algolia_enabled'  => true,
+					'searchable_sites' => [ $site_url ],
+				],
+			]
+		);
+	}
+
+	/**
+	 * Prime the global main query as a frontend search query.
+	 *
+	 * @param string $term Search term.
+	 */
+	private function prime_main_search_query( string $term ): void {
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited, SlevomatCodingStandard.Variables.UnusedVariable.UnusedVariable -- Setting up test global state.
+		global $wp_query, $wp_the_query;
+
+		set_current_screen( 'front' );
+
+		$wp_query     = new \WP_Query(); // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$wp_the_query = $wp_query; // phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited, SlevomatCodingStandard.Variables.UnusedVariable.UnusedVariable
+
+		$wp_query->query( [ 's' => $term ] );
+	}
+}
diff --git a/tests/php/Unit/Modules/Search/SettingsTest.php b/tests/php/Unit/Modules/Search/SettingsTest.php
new file mode 100644
index 0000000..b93e6d9
--- /dev/null
+++ b/tests/php/Unit/Modules/Search/SettingsTest.php
@@ -0,0 +1,413 @@
+<?php
+/**
+ * Search settings unit tests.
+ *
+ * @package OneSearch\Tests\Unit\Modules\Search
+ */
+
+declare(strict_types = 1);
+
+namespace OneSearch\Tests\Unit\Modules\Search;
+
+use OneSearch\Modules\Rest\Governing_Data_Handler;
+use OneSearch\Modules\Search\Settings as Search_Settings;
+use OneSearch\Modules\Settings\Settings;
+use OneSearch\Tests\TestCase;
+use OneSearch\Vendor\Algolia\AlgoliaSearch\Algolia as AlgoliaSDK;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+/**
+ * Tests for the search Settings class.
+ */
+#[CoversClass( \OneSearch\Modules\Search\Settings::class )]
+final class SettingsTest extends TestCase {
+	/**
+	 * {@inheritDoc}
+	 */
+	protected function tearDown(): void {
+		AlgoliaSDK::resetHttpClient();
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Ensures register_hooks adds expected actions.
+	 */
+	public function test_register_hooks_adds_expected_actions(): void {
+		$settings = new Search_Settings();
+		$settings->register_hooks();
+
+		$this->assertNotFalse( has_action( 'admin_init', [ $settings, 'register_settings' ] ) );
+		$this->assertNotFalse( has_action( 'rest_api_init', [ $settings, 'register_settings' ] ) );
+	}
+
+	/**
+	 * Ensures register_hooks listens to site_type, shared_sites option updates.
+	 */
+	public function test_register_hooks_listens_to_site_type_changes(): void {
+		$settings = new Search_Settings();
+		$settings->register_hooks();
+
+		$this->assertNotFalse(
+			has_action( 'update_option_' . Settings::OPTION_SITE_TYPE, [ $settings, 'on_site_type_change' ] )
+		);
+		$this->assertNotFalse(
+			has_action( 'update_option_' . Settings::OPTION_GOVERNING_SHARED_SITES, [ $settings, 'on_shared_sites_change' ] )
+		);
+	}
+
+	/**
+	 * Ensures register_hooks sets up cache purge hooks.
+	 */
+	public function test_register_hooks_sets_up_cache_purge_actions(): void {
+		$settings = new Search_Settings();
+		$settings->register_hooks();
+
+		$this->assertNotFalse(
+			has_action( 'update_option_' . Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS, [ $settings, 'purge_cache_on_update' ] )
+		);
+		$this->assertNotFalse(
+			has_action( 'update_option_' . Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES, [ $settings, 'purge_cache_on_update' ] )
+		);
+		$this->assertNotFalse(
+			has_action( 'update_option_' . Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS, [ $settings, 'purge_cache_on_update' ] )
+		);
+	}
+
+	/**
+	 * Ensures register_settings registers governing settings when governing.
+	 */
+	public function test_register_settings_registers_governing_options(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+
+		$settings = new Search_Settings();
+		$settings->register_settings();
+
+		$registered = get_registered_settings();
+
+		$this->assertArrayHasKey( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS, $registered );
+		$this->assertArrayHasKey( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES, $registered );
+		$this->assertArrayHasKey( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS, $registered );
+	}
+
+			/**
+			 * Ensures register_settings sanitizes algolia credentials payload.
+			 */
+	public function test_register_settings_sanitizes_algolia_credentials(): void {
+		$settings = new Search_Settings();
+		$settings->register_settings();
+
+		$raw = [
+			'app_id'    => ' <b>app-id</b> ',
+			'write_key' => "\n<script>alert(1)</script>write-key\t",
+		];
+
+		update_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS, $raw );
+		$sanitized = get_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$this->assertSame( 'app-id', $sanitized['app_id'] );
+		$this->assertSame( 'write-key', $sanitized['write_key'] );
+	}
+
+	/**
+	 * Ensures register_settings sanitizes search settings payload and normalizes keys.
+	 */
+	public function test_register_settings_sanitizes_search_settings_payload(): void {
+		$settings = new Search_Settings();
+		$settings->register_settings();
+
+		$raw = [
+			' https://example.com/site '  => [
+				'algolia_enabled'  => 1,
+				'searchable_sites' => [ ' https://child.example.com/<b>x</b> ' ],
+			],
+			'https://example.com/invalid' => 'not-array',
+		];
+
+		update_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS, $raw );
+		$sanitized = get_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$this->assertArrayHasKey( 'https://example.com/site/', $sanitized );
+		$this->assertTrue( $sanitized['https://example.com/site/']['algolia_enabled'] );
+		$this->assertSame( [ 'https://child.example.com/x' ], $sanitized['https://example.com/site/']['searchable_sites'] );
+
+		$this->assertArrayHasKey( 'https://example.com/invalid/', $sanitized );
+		$this->assertFalse( $sanitized['https://example.com/invalid/']['algolia_enabled'] );
+		$this->assertSame( [], $sanitized['https://example.com/invalid/']['searchable_sites'] );
+	}
+
+	/**
+	 * Returns null values when no credentials are stored.
+	 */
+	public function test_get_algolia_credentials_returns_nulls_when_empty(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$creds = Search_Settings::get_algolia_credentials();
+
+		$this->assertNull( $creds['app_id'] );
+		$this->assertNull( $creds['write_key'] );
+	}
+
+	/**
+	 * Returns stored credentials after setting them.
+	 */
+	public function test_get_algolia_credentials_returns_stored_values(): void {
+		Search_Settings::set_algolia_credentials(
+			[
+				'app_id'    => 'my-app',
+				'write_key' => 'my-key',
+			]
+		);
+
+		$creds = Search_Settings::get_algolia_credentials();
+
+		$this->assertSame( 'my-app', $creds['app_id'] );
+		$this->assertSame( 'my-key', $creds['write_key'] );
+	}
+
+	/**
+	 * Returns true on successful save.
+	 */
+	public function test_set_algolia_credentials_returns_true_on_success(): void {
+		$result = Search_Settings::set_algolia_credentials(
+			[
+				'app_id'    => 'app',
+				'write_key' => 'key',
+			]
+		);
+
+		$this->assertTrue( $result );
+	}
+
+	/**
+	 * Returns false when value is not an array.
+	 */
+	public function test_set_algolia_credentials_returns_false_for_non_array(): void {
+		// @phpstan-ignore argument.type
+		$result = Search_Settings::set_algolia_credentials( 'invalid' );
+
+		$this->assertFalse( $result );
+	}
+
+	/**
+	 * Stores null when app_id is missing.
+	 */
+	public function test_set_algolia_credentials_stores_null_for_missing_app_id(): void {
+		Search_Settings::set_algolia_credentials( [ 'write_key' => 'a-key' ] );
+
+		$creds = Search_Settings::get_algolia_credentials();
+
+		$this->assertNull( $creds['app_id'] );
+	}
+
+	/**
+	 * Returns empty array when nothing is stored.
+	 */
+	public function test_get_indexable_entities_returns_empty_when_unset(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES );
+
+		$this->assertSame( [], Search_Settings::get_indexable_entities() );
+	}
+
+	/**
+	 * Returns stored value.
+	 */
+	public function test_get_indexable_entities_returns_stored_value(): void {
+		$entities = [
+			'entities' => [
+				'https://example.com/' => [ 'post', 'page' ],
+			],
+		];
+		update_option( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES, $entities );
+
+		$this->assertSame( $entities, Search_Settings::get_indexable_entities() );
+	}
+
+	/**
+	 * Returns empty array when nothing is stored.
+	 */
+	public function test_get_search_settings_returns_empty_when_unset(): void {
+		delete_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$this->assertSame( [], Search_Settings::get_search_settings() );
+	}
+
+	/**
+	 * Returns stored search settings.
+	 */
+	public function test_get_search_settings_returns_stored_value(): void {
+		$value = [
+			'https://example.com/' => [
+				'algolia_enabled'  => true,
+				'searchable_sites' => [ 'https://child.example.com/' ],
+			],
+		];
+		update_option( Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS, $value );
+
+		$this->assertSame( $value, Search_Settings::get_search_settings() );
+	}
+
+	/**
+	 * Does nothing when new value is not consumer.
+	 */
+	public function test_on_site_type_change_skips_non_consumer(): void {
+		$settings = new Search_Settings();
+
+		// Should not throw or error out.
+		$settings->on_site_type_change( '', Settings::SITE_TYPE_GOVERNING );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Deletes Algolia index when site type changes to consumer.
+	 *
+	 * When the site type is updated to 'consumer', on_site_type_change should
+	 * call delete_index() which triggers an Algolia delete request.
+	 */
+	public function test_on_site_type_change_deletes_index_for_consumer(): void {
+		// Set site type to consumer (simulates the option already being saved
+		// before the update_option_ hook fires).
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+		update_option( Settings::OPTION_CONSUMER_PARENT_SITE_URL, 'https://governing.example.com' );
+
+		// Prime brand config cache so Algolia credentials resolve via consumer path.
+		$cached_config = [
+			'algolia_credentials' => [
+				'app_id'    => 'test-app',
+				'write_key' => 'test-key',
+			],
+			'search_settings'     => [
+				'algolia_enabled'  => true,
+				'searchable_sites' => [],
+			],
+			'indexable_entities'  => [ 'post' ],
+			'available_sites'     => [],
+		];
+
+		$method = new \ReflectionMethod( Governing_Data_Handler::class, 'set_brand_config_cache' );
+		$method->invoke( null, $cached_config );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$settings = new Search_Settings();
+		$settings->on_site_type_change( Settings::SITE_TYPE_GOVERNING, Settings::SITE_TYPE_CONSUMER );
+
+		// delete_index() on a consumer site calls deleteBy, which hits Algolia.
+		$this->assertNotEmpty( $recorded_paths, 'Changing to consumer should trigger Algolia delete_index call.' );
+	}
+
+	/**
+	 * Does nothing when old value is empty.
+	 */
+	public function test_on_shared_sites_change_skips_empty_old_value(): void {
+		$settings = new Search_Settings();
+
+		$settings->on_shared_sites_change( [], [ [ 'url' => 'https://new.example.com' ] ] );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Does nothing when old value is not an array.
+	 */
+	public function test_on_shared_sites_change_skips_non_array_old_value(): void {
+		$settings = new Search_Settings();
+
+		$settings->on_shared_sites_change( 'not-array', [ [ 'url' => 'https://new.example.com' ] ] );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Does nothing when no sites have been removed.
+	 */
+	public function test_on_shared_sites_change_skips_when_no_sites_removed(): void {
+		$sites    = [ [ 'url' => 'https://child.example.com' ] ];
+		$settings = new Search_Settings();
+
+		$settings->on_shared_sites_change( $sites, $sites );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Keeps indexable entities unchanged when site removal delete fails.
+	 */
+	public function test_on_shared_sites_change_keeps_entities_when_delete_fails(): void {
+		$settings = new Search_Settings();
+
+		$initial_entities = [
+			'entities' => [
+				'post' => [
+					'https://child-a.example.com/',
+					'https://child-b.example.com/',
+				],
+			],
+		];
+
+		update_option( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES, $initial_entities );
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$old_sites = [
+			[ 'url' => 'https://child-a.example.com/' ],
+			[ 'url' => 'https://child-b.example.com/' ],
+		];
+		$new_sites = [
+			[ 'url' => 'https://child-b.example.com/' ],
+		];
+
+		$settings->on_shared_sites_change( $old_sites, $new_sites );
+
+		$this->assertSame( $initial_entities, get_option( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES ) );
+	}
+
+	/**
+	 * Purges cache when algolia credentials option updates.
+	 */
+	public function test_purge_cache_on_update_clears_cache_for_credentials(): void {
+		set_transient( Governing_Data_Handler::TRANSIENT_KEY, [ 'test' => true ], 3600 );
+
+		$settings = new Search_Settings();
+		$settings->purge_cache_on_update( [], [], Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$this->assertFalse( get_transient( Governing_Data_Handler::TRANSIENT_KEY ) );
+	}
+
+	/**
+	 * Purges cache when indexable sites option updates.
+	 */
+	public function test_purge_cache_on_update_clears_cache_for_indexable_sites(): void {
+		set_transient( Governing_Data_Handler::TRANSIENT_KEY, [ 'test' => true ], 3600 );
+
+		$settings = new Search_Settings();
+		$settings->purge_cache_on_update( [], [], Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES );
+
+		$this->assertFalse( get_transient( Governing_Data_Handler::TRANSIENT_KEY ) );
+	}
+
+	/**
+	 * Purges cache when search settings option updates.
+	 */
+	public function test_purge_cache_on_update_clears_cache_for_search_settings(): void {
+		set_transient( Governing_Data_Handler::TRANSIENT_KEY, [ 'test' => true ], 3600 );
+
+		$settings = new Search_Settings();
+		$settings->purge_cache_on_update( [], [], Search_Settings::OPTION_GOVERNING_SEARCH_SETTINGS );
+
+		$this->assertFalse( get_transient( Governing_Data_Handler::TRANSIENT_KEY ) );
+	}
+
+	/**
+	 * Does not purge cache for unknown option.
+	 */
+	public function test_purge_cache_on_update_ignores_unknown_option(): void {
+		set_transient( Governing_Data_Handler::TRANSIENT_KEY, [ 'test' => true ], 3600 );
+
+		$settings = new Search_Settings();
+		$settings->purge_cache_on_update( [], [], 'some_unrelated_option' );
+
+		$this->assertNotFalse( get_transient( Governing_Data_Handler::TRANSIENT_KEY ) );
+	}
+}
diff --git a/tests/php/Unit/Modules/Search/WatcherTest.php b/tests/php/Unit/Modules/Search/WatcherTest.php
new file mode 100644
index 0000000..be4a8d1
--- /dev/null
+++ b/tests/php/Unit/Modules/Search/WatcherTest.php
@@ -0,0 +1,275 @@
+<?php
+/**
+ * Watcher unit tests.
+ *
+ * @package OneSearch\Tests\Unit\Modules\Search
+ */
+
+declare(strict_types = 1);
+
+namespace OneSearch\Tests\Unit\Modules\Search;
+
+use OneSearch\Modules\Rest\Governing_Data_Handler;
+use OneSearch\Modules\Search\Settings as Search_Settings;
+use OneSearch\Modules\Search\Watcher;
+use OneSearch\Modules\Settings\Settings;
+use OneSearch\Tests\TestCase;
+use OneSearch\Utils;
+use OneSearch\Vendor\Algolia\AlgoliaSearch\Algolia as AlgoliaSDK;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+/**
+ * Tests for the Watcher class.
+ */
+#[CoversClass( \OneSearch\Modules\Search\Watcher::class )]
+final class WatcherTest extends TestCase {
+	/**
+	 * {@inheritDoc}
+	 */
+	protected function tearDown(): void {
+		AlgoliaSDK::resetHttpClient();
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Ensures register_hooks adds transition_post_status action.
+	 */
+	public function test_register_hooks_adds_transition_post_status_action(): void {
+		$watcher = new Watcher();
+		$watcher->register_hooks();
+
+		$this->assertNotFalse( has_action( 'transition_post_status', [ $watcher, 'on_post_transition' ] ) );
+	}
+
+	/**
+	 * Skips when post is not a WP_Post instance.
+	 */
+	public function test_on_post_transition_skips_non_wp_post(): void {
+		$watcher = new Watcher();
+
+		// Should not throw or error out.
+		// @phpstan-ignore argument.type -- Non-WP_Post passed intentionally.
+		$watcher->on_post_transition( 'publish', 'draft', 'not-a-post' );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Skips when post type is not indexable (no entities configured).
+	 */
+	public function test_on_post_transition_skips_non_indexable_post_type(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		// Set indexable entities to only 'page', not 'post'.
+		update_option(
+			Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES,
+			[
+				'entities' => [
+					Utils::normalize_url( get_site_url() ) => [ 'page' ],
+				],
+			]
+		);
+
+		$post    = self::factory()->post->create_and_get( [ 'post_type' => 'post' ] );
+		$watcher = new Watcher();
+
+		// Should exit early without hitting Algolia since 'post' is not indexable.
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Skips when no indexable entities are configured at all.
+	 */
+	public function test_on_post_transition_skips_when_no_entities_configured(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		delete_option( Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES );
+
+		$post    = self::factory()->post->create_and_get();
+		$watcher = new Watcher();
+
+		// Should exit early without hitting Algolia since no indexable entities are configured.
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Processes indexable post types (though Algolia call will fail without credentials,
+	 * we verify it gets past the post_type guard).
+	 */
+	public function test_on_post_transition_processes_indexable_post_type(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		update_option(
+			Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES,
+			[
+				'entities' => [
+					Utils::normalize_url( get_site_url() ) => [ 'post' ],
+				],
+			]
+		);
+		// No Algolia credentials → delete_by will return WP_Error, so on_post_transition
+		// will return early after the failed delete. This tests the flow gets past the
+		// post_type check.
+		delete_option( Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS );
+
+		$post    = self::factory()->post->create_and_get( [ 'post_status' => 'publish' ] );
+		$watcher = new Watcher();
+
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Skips reindexing when new status is not an allowed status (e.g., trashed).
+	 *
+	 * Injects a fake Algolia HTTP client to intercept SDK-level requests (the SDK
+	 * does not use wp_remote_*, so pre_http_request cannot be used here). After
+	 * transitioning to 'trash', only the deleteBy call should have been made — no
+	 * /batch (saveObjects) request should appear.
+	 */
+	public function test_on_post_transition_does_not_reindex_disallowed_status(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+		update_option( Settings::OPTION_CONSUMER_PARENT_SITE_URL, 'https://governing.example.com' );
+
+		$this->set_consumer_brand_config_cache();
+
+		// Intercept every Algolia SDK HTTP call and record the request paths.
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$post    = self::factory()->post->create_and_get( [ 'post_status' => 'publish' ] );
+		$watcher = new Watcher();
+
+		// Transitioning to 'trash' should delete from the index but must not reindex.
+		$watcher->on_post_transition( 'trash', 'publish', $post );
+
+		// deleteBy was called (some path was recorded), but no /batch (saveObjects) call
+		// should have been made — the status guard must have stopped reindexing.
+		$batch_calls = array_filter( $recorded_paths, static fn ( $p ) => str_contains( $p, '/batch' ) );
+		$this->assertEmpty( $batch_calls, 'Trash transition should perform delete only and must not reindex.' );
+	}
+
+	/**
+	 * Consumer site attempts to fetch allowed post types from brand config.
+	 */
+	public function test_on_post_transition_consumer_site_checks_brand_config(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+		delete_option( Settings::OPTION_CONSUMER_PARENT_SITE_URL );
+		delete_transient( Governing_Data_Handler::TRANSIENT_KEY );
+
+		$post    = self::factory()->post->create_and_get();
+		$watcher = new Watcher();
+
+		// No parent URL → get_brand_config returns WP_Error → post type is not indexable.
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Consumer site with cached brand config recognizes indexable post types.
+	 */
+	public function test_on_post_transition_consumer_with_cached_config(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+		update_option( Settings::OPTION_CONSUMER_PARENT_SITE_URL, 'https://governing.example.com' );
+
+		$this->set_consumer_brand_config_cache( 'test-app', 'test-key' );
+
+		$post    = self::factory()->post->create_and_get( [ 'post_status' => 'publish' ] );
+		$watcher = new Watcher();
+
+		// 'post' is in indexable_entities, so it passes the guard.
+		// Algolia SDK will fail with test credentials, but the guard logic is tested.
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		$this->assertTrue( true );
+	}
+
+	/**
+	 * Prime the consumer brand config cache used by Watcher guards.
+	 *
+	 * @param string $app_id    Algolia app ID.
+	 * @param string $write_key Algolia write key.
+	 */
+	private function set_consumer_brand_config_cache( string $app_id = 'TEST_APP', string $write_key = 'TEST_KEY' ): void {
+		$cached_config = [
+			'algolia_credentials' => [
+				'app_id'    => $app_id,
+				'write_key' => $write_key,
+			],
+			'search_settings'     => [
+				'algolia_enabled'  => true,
+				'searchable_sites' => [],
+			],
+			'indexable_entities'  => [ 'post' ],
+			'available_sites'     => [],
+		];
+
+		$method = new \ReflectionMethod( Governing_Data_Handler::class, 'set_brand_config_cache' );
+		$method->invoke( null, $cached_config );
+	}
+
+	/**
+	 * Indexable post triggers Algolia saveObjects (reindex) call.
+	 * This verifies the full integration flow for a governing site.
+	 */
+	public function test_on_post_transition_triggers_algolia_reindex(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_GOVERNING );
+		update_option(
+			Search_Settings::OPTION_GOVERNING_ALGOLIA_CREDENTIALS,
+			[
+				'app_id'    => 'test-app',
+				'write_key' => 'test-key',
+			]
+		);
+		update_option(
+			Search_Settings::OPTION_GOVERNING_INDEXABLE_SITES,
+			[
+				'entities' => [
+					Utils::normalize_url( get_site_url() ) => [ 'post' ],
+				],
+			]
+		);
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$post    = self::factory()->post->create_and_get( [ 'post_status' => 'publish' ] );
+		$watcher = new Watcher();
+
+		// Transition from 'draft' to 'publish' (should trigger reindex).
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		// Assert that a /batch (saveObjects) call was made.
+		$batch_calls = array_filter( $recorded_paths, static fn ( $p ) => str_contains( $p, '/batch' ) );
+		$this->assertNotEmpty( $batch_calls, 'Happy path should trigger Algolia reindex (saveObjects).' );
+	}
+
+	/**
+	 * Indexable post triggers Algolia saveObjects (reindex) call on a consumer (brand) site.
+	 * This verifies the full integration flow where credentials and indexable entities
+	 * are resolved from the governing site's brand config cache.
+	 */
+	public function test_on_post_transition_triggers_algolia_reindex_consumer_site(): void {
+		update_option( Settings::OPTION_SITE_TYPE, Settings::SITE_TYPE_CONSUMER );
+		update_option( Settings::OPTION_CONSUMER_PARENT_SITE_URL, 'https://governing.example.com' );
+
+		$this->set_consumer_brand_config_cache( 'test-app', 'test-key' );
+
+		$recorded_paths = [];
+		$this->mock_algolia_http_client( $recorded_paths );
+
+		$post    = self::factory()->post->create_and_get( [ 'post_status' => 'publish' ] );
+		$watcher = new Watcher();
+
+		// Transition from 'draft' to 'publish' (should trigger reindex).
+		$watcher->on_post_transition( 'publish', 'draft', $post );
+
+		// Assert that a /batch (saveObjects) call was made.
+		$batch_calls = array_filter( $recorded_paths, static fn ( $p ) => str_contains( $p, '/batch' ) );
+		$this->assertNotEmpty( $batch_calls, 'Consumer site happy path should trigger Algolia reindex (saveObjects).' );
+	}
+}