Custom Test Fixtures

Overview

Langflow extends Playwright's default test and expect with a custom fixture in src/frontend/tests/fixtures.ts. This fixture adds automatic error detection that fails tests when unexpected API errors or flow execution errors occur.

Why Custom Fixtures Exist

Without the custom fixture, a test could pass even though:

• The backend returned a 500 Internal Server Error (test only checked for UI text)
• A flow build silently failed with a Python exception (test only checked button state)
• An API call returned 404 because the resource was deleted (test didn't check the response)

The custom fixture catches these silent failures by monitoring ALL /api/ responses during the test.

Import Rule

Always import from ../../fixtures, never from @playwright/test:

// Right — includes error detection
import { expect, test } from "../../fixtures";

// Wrong — NO error detection, silent failures possible
import { expect, test } from "@playwright/test";

What the Fixture Detects

HTTP Error Responses

The fixture intercepts all responses from /api/ endpoints and fails the test if:

Flow Execution Errors

For streaming responses (build, chat), the fixture parses the event stream and fails if:

• JSON payload contains "error": true
• Response body contains Python exception patterns (Traceback, Error, etc.)
• The stream indicates a component build failure

Allowing Expected Errors

Some tests intentionally trigger errors (testing error handling, validation feedback, etc.). Use page.allowFlowErrors() to prevent the fixture from failing on flow execution errors:

test("should show error message on invalid component config", { tag: ["@release"] }, async ({ page }) => {
  page.allowFlowErrors();  // Allow flow errors for THIS test only

  await awaitBootstrapTest(page);
  // ... test that triggers an error ...

  await expect(page.getByText(/error/i)).toBeVisible();
});

Note: allowFlowErrors() only suppresses flow execution errors. HTTP 500 errors will still fail the test — those indicate a backend crash, not expected behavior.

Error Reporting

When the fixture detects an error, it adds it to an internal list. After the test function completes, the fixture checks the list and fails with a descriptive message:

Test failed due to unexpected API errors:
  - POST /api/v1/build/abc123/flow → 500 Internal Server Error
  - Flow execution error: Traceback (most recent call last)...

This makes it easy to identify the root cause without adding manual response checks to every test.

Timeout Behavior

The fixture reads response bodies with a 2-second timeout. If the body can't be read within 2 seconds (e.g., streaming response still in progress), it skips body parsing for that response. This prevents the fixture from blocking indefinitely on long-running streams.

Global Teardown

src/frontend/tests/globalTeardown.ts runs after all tests complete and removes the temporary test database. This ensures a clean state for the next test run.