codegen: add foreign key error check test

pkg/db/errors_test_helper.go

@@ -0,0 +1,21 @@
+package db
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func AssertForeignKeyError[T ForeignKey](t *testing.T, err error, field string, val T) {
+	t.Helper()
+
+	var fkErr ForeignKeyError[T]
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrForeignKeyViolation)
+	// ErrorAs produces terrible error messages if it's a ForeignKeyError with a different type
+	// parameter (i.e., if it was a different field that failed).
+	require.ErrorAs(t, err, &fkErr, "expected error field: %q", field)
+	assert.Equal(t, field, fkErr.Field)
+	assert.Equal(t, val, fkErr.FkValue)
+}