Phoenix Playwright Test Writing

Write end-to-end tests for Phoenix using Playwright. Tests live in js/app/tests/ and follow established patterns.

Timeout Policy

• Do not pass timeout args in test code under js/app/tests.
• Tune timing centrally in js/app/playwright.config.ts (global timeout, expect.timeout, use.navigationTimeout, and webServer.timeout).

Quick Start

import { expect, test } from "@playwright/test";
import { randomUUID } from "crypto";

test.describe("Feature Name", () => {
  test.beforeEach(async ({ page }) => {
    await page.goto(`/login`);
    await page.getByLabel("Email").fill("admin@localhost");
    await page.getByLabel("Password").fill("admin123");
    await page.getByRole("button", { name: "Log In", exact: true }).click();
    await page.waitForURL("**/projects");
  });

  test("can do something", async ({ page }) => {
    // Test implementation
  });
});

Test Credentials

Selector Patterns (Priority Order)

1. Role selectors (most robust):

   page.getByRole("button", { name: "Save" });
   page.getByRole("link", { name: "Datasets" });
   page.getByRole("tab", { name: /Evaluators/i });
   page.getByRole("menuitem", { name: "Edit" });
   page.getByRole("cell", { name: "my-item" });
   page.getByRole("heading", { name: "Title" });
   page.getByRole("dialog");
   page.getByRole("textbox", { name: "Name" });
   page.getByRole("combobox", { name: /mapping/i });

2. Label selectors:

   page.getByLabel("Email");
   page.getByLabel("Dataset Name");
   page.getByLabel("Description");

3. Text selectors:

   page.getByText("No evaluators added");
   page.getByPlaceholder("Search...");

4. Test IDs (when available):

   page.getByTestId("create-dataset-button");
   // element with state — select the stable id, filter on the data attribute
   page.locator('[data-testid="llm-evaluator-form-submit-button"][data-mode="create"]');

   data-testids are scoped, fully spelled out (...-button, never ...-btn), and constant regardless of state — state is exposed via a sibling data-* attribute (data-mode, data-state, …), so never key a getByTestId off a value that only exists in one mode. If you need a data-testid that doesn't exist yet, add it following references/test-ids.md in the phoenix-frontend skill (pattern: <scope>-<subject>-<role>).

5. CSS locators (last resort):

   page.locator('button:has-text("Save")');

Common UI Patterns

Dropdown Menus

// Click button to open dropdown
await page.getByRole("button", { name: "New Dataset" }).click();
// Select menu item
await page.getByRole("menuitem", { name: "New Dataset" }).click();

Nested Menus (Submenus)

// Open menu, hover over submenu trigger, click submenu item
await page.getByRole("button", { name: "Add evaluator" }).click();
await page
  .getByRole("menuitem", { name: "Use LLM evaluator template" })
  .hover();
await page.getByRole("menuitem", { name: /correctness/i }).click();

// IMPORTANT: Always use getByRole("menuitem") for submenu items, not getByText()
// Playwright's auto-waiting handles the submenu appearance timing
// ❌ BAD - flaky in CI:
// await page.getByText("ExactMatch").first().click();
// ✅ GOOD - reliable:
// await page.getByRole("menuitem", { name: /ExactMatch/i }).click();

Dialogs/Modals

// Wait for dialog
await expect(page.getByRole("dialog")).toBeVisible();
// Fill form in dialog
await page.getByLabel("Name").fill("test-name");
// Submit
await page.getByRole("button", { name: "Create" }).click();
// Wait for close
await expect(page.getByRole("dialog")).not.toBeVisible();

Tables with Row Actions

// Find row by cell content
const row = page.getByRole("row").filter({
  has: page.getByRole("cell", { name: "item-name" }),
});
// Click action button in row (usually last button)
await row.getByRole("button").last().click();
// Select action from menu
await page.getByRole("menuitem", { name: "Edit" }).click();

Tabs

await page.getByRole("tab", { name: /Evaluators/i }).click();
await page.waitForURL("**/evaluators");
await expect(page.getByRole("tab", { name: /Evaluators/i })).toHaveAttribute(
  "aria-selected",
  "true",
);

Form Inputs in Sections

// When multiple textboxes exist, scope to section
const systemSection = page.locator('button:has-text("System")');
const systemTextbox = systemSection
  .locator("..")
  .locator("..")
  .getByRole("textbox");
await systemTextbox.fill("content");

Serial Tests (Shared State)

Use test.describe.serial when tests depend on each other:

test.describe.serial("Workflow", () => {
  const itemName = `item-${randomUUID()}`;

  test("step 1: create item", async ({ page }) => {
    // Creates itemName
  });

  test("step 2: edit item", async ({ page }) => {
    // Uses itemName from previous test
  });

  test("step 3: verify edits", async ({ page }) => {
    // Verifies itemName was edited
  });
});

Assertions

// Visibility
await expect(element).toBeVisible();
await expect(element).not.toBeVisible();

// Text content
await expect(element).toHaveText("expected");
await expect(element).toContainText("partial");

// Attributes
await expect(element).toHaveAttribute("aria-selected", "true");

// Input values
await expect(input).toHaveValue("expected value");

// URL
await page.waitForURL("**/datasets/**/examples");

Navigation Patterns

// Direct navigation
await page.goto("/datasets");
await page.waitForURL("**/datasets");

// Click navigation
await page.getByRole("link", { name: "Datasets" }).click();
await page.waitForURL("**/datasets");

// Extract ID from URL
const url = page.url();
const match = url.match(/datasets\/([^/]+)/);
const datasetId = match ? match[1] : "";

// Navigate with query params
await page.goto(`/playground?datasetId=${datasetId}`);

Running Tests

Before running Playwright tests, build the app so E2E runs against the latest frontend changes:

pnpm run build

# Run specific test file
pnpm exec playwright test tests/server-evaluators.spec.ts --project=chromium

# Run with UI mode
pnpm exec playwright test --ui

# Run specific test by name
pnpm exec playwright test -g "can create"

# Debug mode
pnpm exec playwright test --debug

Avoiding Interactive Report Server

By default, Playwright serves an HTML report after tests finish and waits for Ctrl+C, which can cause command timeouts. Use these options to avoid this:

# Use list reporter (no interactive server)
pnpm exec playwright test tests/example.spec.ts --project=chromium --reporter=list

# Use dot reporter for minimal output
pnpm exec playwright test tests/example.spec.ts --project=chromium --reporter=dot

# Set CI mode to disable interactive features
CI=1 pnpm exec playwright test tests/example.spec.ts --project=chromium

Recommended for automation: Always use --reporter=list or CI=1 when running tests programmatically to ensure the command exits cleanly after tests complete.

Phoenix-Specific Pages

UI Exploration

When selectors are unclear, use the available browser tooling to explore the Phoenix UI at http://localhost:6006/datasets. Inspect accessible roles and names, interact with the target elements, and inspect the page again after navigation or DOM changes.

Use the observed roles and names to choose Playwright selectors:

File Naming

• Feature tests: {feature-name}.spec.ts
• Access control: {role}-access.spec.ts
• Rate limiting: {feature}.rate-limit.spec.ts (runs last)

Common Gotchas

1. Dialog not closing: Wait for a deterministic post-action signal (e.g., dialog hidden + success row visible)
2. Multiple elements: Use .first(), .last(), or .nth(n)
3. Dynamic content: Use regex in name: { name: /pattern/i }
4. Flaky waits: Prefer waitForURL over waitForTimeout
5. Menu not appearing: Wait for specific menu state/element visibility

Debugging Flaky Tests

Critical Lessons Learned

1. Don't assume parallelism is the problem

   • Phoenix tests run with 7 parallel workers without issues
   • The app handles concurrent logins, database operations, and session management properly
   • If tests fail with parallelism, it's usually a test timing issue, not infrastructure
   • Playwright's browser context isolation is robust - each worker gets isolated cookies/sessions

2. waitForTimeout is almost always wrong

   • page.waitForTimeout() is the #1 cause of flakiness in Phoenix tests
   • Arbitrary timeouts race against rendering and network speed
   • Always replace with state-based waits:

     // ❌ BAD - flaky, races against rendering
     await page.waitForTimeout(500);
     await element.click();
     
     // ✅ GOOD - waits for actual state
     await element.waitFor({ state: "visible" });
     await element.click();

3. Test the actual failure before fixing

   • Run tests with parallelism enabled to see what actually fails
   • Check error messages - they often point to the real issue
   • Don't optimize prematurely (e.g., caching auth state) if it's not the problem

4. Phoenix test infrastructure is solid

   • In-memory SQLite works fine with parallel tests
   • No need for per-worker databases
   • No need for auth state caching
   • Tests use randomUUID() for data isolation - this works well

Debugging Workflow

When tests are flaky:

1. Run with parallelism multiple times to catch intermittent failures:

   for i in 1 2 3 4 5; do
     pnpm exec playwright test --project=chromium --reporter=dot
   done

2. Look for waitForTimeout usage - replace with proper waits:

   grep -r "waitForTimeout" js/app/tests/

3. Check for race conditions in element interactions:

   • Wait for element visibility before interacting
   • Wait for network idle when needed: page.waitForLoadState("networkidle")
   • Use waitForURL after navigation actions

4. Verify selectors are stable:

   • Avoid CSS selectors that depend on DOM structure
   • Use role/label selectors that match ARIA attributes
   • Test selectors don't break when UI updates

5. Run with trace on failure to see what happened:

   pnpm exec playwright test --trace on-first-retry

Common Flaky Patterns and Fixes

Test Stability Best Practices

1. Use proper waits:

   // Wait for element state
   await element.waitFor({ state: "visible" | "hidden" | "attached" })
   
   // Wait for network
   await page.waitForLoadState("networkidle" | "domcontentloaded" | "load")
   
   // Wait for URL change
   await page.waitForURL("**/expected-path")

2. Use unique test data:

   const uniqueName = `test-${randomUUID()}`;

3. Prefer role selectors - they're less brittle:

   page.getByRole("button", { name: "Save" }) // ✅ Good
   page.locator('button.save-btn') // ❌ Brittle

4. Don't fight animations - wait for them:

   await expect(dialog).not.toBeVisible();

5. Verify URL changes after navigation:

   await page.waitForURL("**/datasets");