diff --git a/tests/TheArchiveCarriesNoTestsTest.php b/tests/TheArchiveCarriesNoTestsTest.php
new file mode 100644
index 0000000..f459822
--- /dev/null
+++ b/tests/TheArchiveCarriesNoTestsTest.php
@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * This file is part of Milpa Command — the Command-as-atom core of the Milpa PHP framework.
+ *
+ * (c) Rodrigo Vicente - TeamX Agency — https://teamx.agency <hola@teamx.agency>
+ *
+ * @license Apache-2.0
+ *
+ * @link    https://github.com/getmilpa/command
+ */
+
+declare(strict_types=1);
+
+namespace Milpa\Command\Tests;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * WHAT A HOUSE INSTALLS OF THIS PACKAGE CARRIES NO TESTS.
+ *
+ * Composer installs the archive of a tag, and git leaves out of an archive whatever `.gitattributes` marks
+ * `export-ignore`. Until that line existed, a house that required this package received its tests too — as
+ * many files as the code it runs, never run there, and with them whatever a test had been written with. One
+ * line keeps them out, and nothing in the package held that line.
+ *
+ * @guards the tests being marked out of the archive, and the archive git builds carrying none
+ *
+ * @refuses nothing — it holds a line of `.gitattributes`
+ */
+final class TheArchiveCarriesNoTestsTest extends TestCase
+{
+    public function testTheTestsAreMarkedOutOfTheArchive(): void
+    {
+        $marked = array_map('trim', file(\dirname(__DIR__) . '/.gitattributes', \FILE_IGNORE_NEW_LINES | \FILE_SKIP_EMPTY_LINES) ?: []);
+
+        self::assertContains('/tests export-ignore', $marked, 'the tests travel to every house that installs this package');
+    }
+
+    /** By execution: the archive git builds of this very commit, listed. */
+    public function testTheArchiveGitBuildsOfThisCommitCarriesNone(): void
+    {
+        $root = \dirname(__DIR__);
+        if (!file_exists($root . '/.git')) {
+            self::markTestSkipped('not a git checkout: there is no archive to build here');
+        }
+
+        exec('git -C ' . escapeshellarg($root) . ' archive HEAD 2>/dev/null | tar -t 2>/dev/null', $entries, $exit);
+        if ($exit !== 0 || $entries === []) {
+            self::markTestSkipped('git could not build the archive of HEAD here');
+        }
+
+        self::assertSame([], array_values(array_filter($entries, static fn (string $entry): bool => str_starts_with($entry, 'tests/'))));
+        self::assertNotSame([], array_filter($entries, static fn (string $entry): bool => str_starts_with($entry, 'src/')), 'the control: the archive was read, and it carries the code');
+    }
+}