Langflow E2E Testing (Playwright)

When to Apply

• User asks to write E2E tests for a feature or flow
• User asks to fix a failing E2E test
• User asks to review E2E test coverage
• User modifies data-testid attributes in components (may break existing tests)
• User changes test utilities in src/frontend/tests/utils/

Do NOT apply when:

• User asks about unit tests (use frontend-testing skill for Jest)
• User asks about backend tests (use backend-code-review skill for pytest)

Tech Stack

Key Commands

# Run all E2E tests
npx playwright test

# Run tests filtered by tag
npx playwright test --grep "@release"
npx playwright test --grep "@workspace"
npx playwright test --grep "@starter-projects"

# Run a specific test file
npx playwright test tests/core/features/run-flow.spec.ts

# Debug mode (headed browser + step through)
npx playwright test --debug

# Show HTML report after run
npx playwright show-report

# Update snapshots (if used)
npx playwright test --update-snapshots

Configuration

File: src/frontend/playwright.config.ts

WebServer: Playwright auto-starts backend (uvicorn on 7860) + frontend (npm start on 3000).

Directory Structure

src/frontend/tests/
├── fixtures.ts                     # Custom test fixture with error detection
├── globalTeardown.ts               # Cleanup (removes temp DB after tests)
├── core/
│   ├── features/                   # Main feature tests (run-flow, playground, etc.)
│   ├── integrations/               # Starter project / template tests
│   ├── regression/                 # Bug regression tests
│   └── unit/                       # Component-level Playwright tests
├── extended/
│   ├── features/                   # Extended features (MCP, auto-save, etc.)
│   ├── integrations/               # Extended integrations
│   └── regression/                 # Extended regressions
└── utils/                          # 37+ shared helper functions

File Naming

• kebab-case with .spec.ts suffix: run-flow.spec.ts, playground.spec.ts, flow-lock.spec.ts
• Template tests may use spaces: Document QA.spec.ts, Social Media Agent.spec.ts
• Sharded tests for parallelization: chatInputOutputUser-shard-0.spec.ts

Note: E2E tests use .spec.ts (Playwright convention). Unit tests use .test.tsx (Jest convention). Do not mix them.

Test Anatomy

Basic Test

import { expect, test } from "../../fixtures";
import { awaitBootstrapTest } from "../../utils/await-bootstrap-test";

test(
  "user should be able to run a flow successfully",
  { tag: ["@release", "@workspace"] },
  async ({ page }) => {
    await awaitBootstrapTest(page);

    // Arrange: Create a flow
    await page.getByTestId("blank-flow").click();

    // Act: Add components and run
    await page.getByTestId("sidebar-search-input").fill("Chat Output");
    // ... setup ...

    // Assert: Verify result
    await expect(page.getByTestId("build-status-success")).toBeVisible({ timeout: 30000 });
  },
);

With test.describe

test.describe("Flow Lock Feature", () => {
  test(
    "should lock and unlock a flow",
    { tag: ["@release", "@api"] },
    async ({ page }) => {
      // ...
    },
  );

  test(
    "should prevent editing when locked",
    { tag: ["@release"] },
    async ({ page }) => {
      // ...
    },
  );
});

With Serial Mode (tests that depend on order)

test.describe.configure({ mode: "serial" });

test("step 1: create flow", async ({ page }) => { /* ... */ });
test("step 2: edit flow", async ({ page }) => { /* ... */ });
test("step 3: delete flow", async ({ page }) => { /* ... */ });

With Event Delivery Modes (streaming/polling/direct)

import { withEventDeliveryModes } from "../../utils/withEventDeliveryModes";

withEventDeliveryModes(
  "Document Q&A should work",
  { tag: ["@release", "@starter-projects"] },
  async ({ page }) => {
    // This test runs 3 times: streaming, polling, direct
    // Each mode is configured automatically via route interception
  },
);

Tags System

Every test MUST have at least one tag. Tags enable filtering and CI pipeline configuration.

// Right: tag your test
test("my feature test", { tag: ["@release", "@workspace"] }, async ({ page }) => { ... });

// Wrong: no tags — test can't be filtered
test("my feature test", async ({ page }) => { ... });

Custom Fixtures: Error Detection

Always import test and expect from ../../fixtures, NOT from @playwright/test.

// Right
import { expect, test } from "../../fixtures";

// Wrong — bypasses error detection
import { expect, test } from "@playwright/test";

Why: The custom fixture automatically monitors all /api/ responses and fails the test if:

• HTTP 400, 404, 422, or 500 errors occur
• Flow execution returns error: true in event streams
• Python exceptions appear in streamed responses

To opt-in to expected errors (e.g., testing error handling):

test("should show error on invalid input", { tag: ["@release"] }, async ({ page }) => {
  page.allowFlowErrors();  // Allow flow errors for this test
  // ... test that expects errors ...
});

Selector Strategy

Priority (in order of preference)

1. getByTestId — Most stable, used 95% of the time in Langflow
2. getByRole — For buttons, headings, and form elements
3. getByText — For visible text content
4. waitForSelector — For CSS selectors and dynamic elements
5. locator — For complex selectors (CSS, XPath)

Common data-testid Patterns

Canvas & Navigation:

• blank-flow — New blank flow button
• sidebar-search-input — Component search
• canvas_controls_dropdown — Canvas controls menu
• fit_view, zoom_out, zoom_in — Canvas controls
• react-flow-id — ReactFlow canvas container

Component Fields:

• popover-anchor-input-{fieldname} — Input field for a component parameter
• input-chat-playground — Playground chat input
• div-chat-message — Chat message in playground

Actions:

• add-component-button-{component} — Add component to canvas
• button-send — Send chat message
• button_run_{component} — Run specific component
• publish-button, save-flow-button — Flow actions
• edit-fields-button — Toggle inspection panel field editor

Modals & Panels:

• modal-title — Modal heading
• icon-Globe — Global variables
• icon-Lock — Flow lock toggle
• session-selector — Playground session switcher

Important: Global Variables and Badges

When a component field has a global variable selected (load_from_db: true + value: "OPENAI_API_KEY"), the field renders a badge instead of an <input> element. This means getByTestId("popover-anchor-input-api_key") will NOT find the element — it doesn't exist in the DOM.

Templates with global variables pre-selected: Market Research, Price Deal Finder, Research Agent. Templates without (input IS rendered): Instagram Copywriter.

Core Helper Functions

Located in src/frontend/tests/utils/:

initialGPTsetup Options

await initialGPTsetup(page);  // All steps

await initialGPTsetup(page, {
  skipAdjustScreenView: true,
  skipUpdateOldComponents: true,
  skipSelectGptModel: true,
});

Inspection Panel Pattern (CRITICAL)

// MUST enable inspection panel FIRST
await enableInspectPanel(page);

// Click a node to select it
await page.getByTestId("title-OpenAI").click();

// Open field editor
await page.getByTestId("edit-fields-button").click();

// Toggle field visibility
await page.getByTestId("showmodel_name").click();

// Close field editor
await page.getByTestId("edit-fields-button").click();

If you skip enableInspectPanel(page), the edit-fields-button will NOT be visible.

Skip Patterns

// Skip test if env var missing
test.skip(!process?.env?.OPENAI_API_KEY, "OPENAI_API_KEY required to run this test");

// Skip test unconditionally with reason
test.skip(true, "Feature not yet implemented with new designs");

Writing Good E2E Tests

Do:

• Tag every test with at least one tag
• Import from ../../fixtures, not @playwright/test
• Start with awaitBootstrapTest(page) — always
• Use getByTestId for stable selectors
• Set explicit timeouts on waitForSelector and expect(...).toBeVisible() for async operations
• Test the complete user flow: setup → action → verification
• Use withEventDeliveryModes for tests that involve flow execution (chat, build)

Don't:

• Don't use page.waitForTimeout() unless absolutely necessary — prefer waitForSelector or expect().toBeVisible()
• Don't hardcode API keys — read from process.env.OPENAI_API_KEY
• Don't skip tests without a reason — always provide the second argument to test.skip()
• Don't import from @playwright/test — use the custom fixtures
• Don't forget enableInspectPanel(page) before accessing edit-fields-button
• Don't assume input fields exist when global variables are selected (badge renders instead)

Challenge Tests (Apply Here Too)

E2E tests should also cover adversarial scenarios:

• Invalid input: paste 10K characters, special characters (<script>alert(1)</script>), empty submissions
• Network interruption: what happens if the user loses connection mid-build?
• Permission boundaries: can a user access another user's flow via direct URL?
• Concurrent actions: double-click delete, rapid chat messages
• Error recovery: does the UI recover gracefully from a 500 error?

References

• Selector Patterns — Complete data-testid catalog
• Helper Functions — Detailed documentation of all 37+ utility functions
• Test Fixtures — Custom fixture error detection behavior