diff --git a/GEMINI.md b/GEMINI.md
index 5784027e..25fb353c 100644
--- a/GEMINI.md
+++ b/GEMINI.md
@@ -60,3 +60,4 @@ Any pull request modifying or extending the driver's features must include:
 - **Mock Server Tests**: Located in files such as `driver_with_mockserver_test.go`, `conn_with_mockserver_test.go`, and `stmt_with_mockserver_test.go`. Use these (or add new test files) to mock Spanner gRPC API responses (e.g. BeginTransaction, Commit, ExecuteSql) and verify that the driver translates options, tags, and states correctly.
 - **Emulator Tests**: Validate integration behavior against the Cloud Spanner Emulator (`integration_test.go` and examples). Make sure the test configurations can run locally with `auto_config_emulator=true`.
 - **Wrapper Tests**: If you modified `spannerlib`, ensure you trigger or run unit/integration tests for the respective wrappers (`python-spanner-lib-wrapper-unit-tests.yml`, `ruby-wrapper-tests.yml`, etc.).
+- **Subtests & Early Failure**: Prefer using Go subtests (`t.Run`) to isolate distinct test cases. When an intermediate setup step fails (e.g., helper function error, unexpected nil, client initialization failure), use `t.Fatalf` or `t.Fatal` to fail and abort that specific test/subtest immediately. Avoid using `t.Errorf` or `t.Error` if subsequent assertions rely on values or state from the failed step, as this results in redundant and confusing secondary error outputs.
diff --git a/stmt_test.go b/stmt_test.go
index d725c737..17404e02 100644
--- a/stmt_test.go
+++ b/stmt_test.go
@@ -17,9 +17,46 @@ package spannerdriver
 import (
 	"database/sql/driver"
 	"reflect"
+	"strings"
 	"testing"
+
+	"cloud.google.com/go/spanner/admin/database/apiv1/databasepb"
+	"github.com/googleapis/go-sql-spanner/connectionstate"
+	"github.com/googleapis/go-sql-spanner/parser"
 )
 
+func TestPrepareSpannerStmt(t *testing.T) {
+	state := createInitialConnectionState(connectionstate.TypeNonTransactional, nil)
+	p, err := parser.NewStatementParser(databasepb.DatabaseDialect_GOOGLE_STANDARD_SQL, 1000)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("QueryParameterNameMatchesExactly", func(t *testing.T) {
+		stmt, err := prepareSpannerStmt(state, p, "SELECT * FROM Singers WHERE SingerId = @id", []driver.NamedValue{
+			{Name: "id", Value: int64(1)},
+		})
+		if err != nil {
+			t.Fatalf("Unexpected error for matching parameter name: %v", err)
+		}
+		if got, want := stmt.Params["id"], int64(1); got != want {
+			t.Errorf("Params[\"id\"] = %v, want %v", got, want)
+		}
+	})
+
+	t.Run("QueryParameterNameMismatch", func(t *testing.T) {
+		_, err := prepareSpannerStmt(state, p, "SELECT * FROM Singers WHERE SingerId = @singer_id", []driver.NamedValue{
+			{Name: "id", Value: int64(1)},
+		})
+		if err == nil {
+			t.Fatal("Expected error for mismatched parameter name, got nil")
+		}
+		if !strings.Contains(err.Error(), "missing value for query parameter @singer_id") {
+			t.Fatalf("Expected 'missing value for query parameter @singer_id' error, got %v", err)
+		}
+	})
+}
+
 func TestConvertParam(t *testing.T) {
 	check := func(in, want driver.Value) {
 		t.Helper()
diff --git a/stmt_with_mockserver_test.go b/stmt_with_mockserver_test.go
index d9ade319..4e92487c 100644
--- a/stmt_with_mockserver_test.go
+++ b/stmt_with_mockserver_test.go
@@ -943,3 +943,20 @@ func executeParamTest(t *testing.T, test paramTest, server *testutil.MockedSpann
 		}
 	}
 }
+
+func TestQueryMismatchedParameterName(t *testing.T) {
+	t.Parallel()
+
+	db, _, teardown := setupTestDBConnection(t)
+	defer teardown()
+	ctx := context.Background()
+
+	// SELECT with @my_id parameter but passing named parameter "id" instead
+	_, err := db.QueryContext(ctx, "select value from test where id=@my_id", sql.Named("id", 123))
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "missing value for query parameter @my_id") {
+		t.Fatalf("expected missing value error, got: %v", err)
+	}
+}