Make MustNotInsert stricter

Add a stricter version of `MustNotInsert` which expects the insert
operation to fail with a specific error code.

pkg/migrations/op_common_test.go

@@ -492,12 +492,22 @@ func MustInsert(t *testing.T, db *sql.DB, schema, version, table string, record
 	}
 }
 
-func MustNotInsert(t *testing.T, db *sql.DB, schema, version, table string, record map[string]string) {
+func MustNotInsert(t *testing.T, db *sql.DB, schema, version, table string, record map[string]string, errorCode string) {
 	t.Helper()
 
-	if err := insert(t, db, schema, version, table, record); err == nil {
+	err := insert(t, db, schema, version, table, record)
+	if err == nil {
 		t.Fatal("Expected INSERT to fail")
 	}
+
+	var pqErr *pq.Error
+	if ok := errors.As(err, &pqErr); ok {
+		if pqErr.Code.Name() != errorCode {
+			t.Fatalf("Expected INSERT to fail with %q, got %q", errorCode, pqErr.Code.Name())
+		}
+	} else {
+		t.Fatalf("INSERT failed with unknown error: %v", err)
+	}
 }
 
 func insert(t *testing.T, db *sql.DB, schema, version, table string, record map[string]string) error {

pkg/testutils/error_codes.go

@@ -0,0 +1,8 @@
+package testutils
+
+const (
+	CheckViolationErrorCode   string = "check_violation"
+	FKViolationErrorCode      string = "foreign_key_violation"
+	NotNullViolationErrorCode string = "not_null_violation"
+	UniqueViolationErrorCode  string = "unique_violation"
+)