E2e Tests StudioCAUTION

Mastra is the modern TypeScript framework for AI-powered applications and agents.

The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
name: e2e-tests-studio
description: >
  REQUIRED when modifying any file in packages/playground-ui or packages/playground.
  Triggers on: React component creation/modification/refactoring, UI changes,
  new playground features, bug fixes affecting studio UI. Generates Playwright E2E tests
  that validate PRODUCT BEHAVIOR, not just UI states.
model: claude-opus-4-5
---

# E2E Behavior Validation for Frontend Modifications

## Core Principle: Test Product Behavior, Not UI States

**CRITICAL**: Tests must verify that product features WORK correctly, not just that UI elements render.

### What NOT to test (UI States):

- ❌ "Dropdown opens when clicked"
- ❌ "Modal appears after button click"
- ❌ "Loading spinner shows during request"
- ❌ "Form fields are visible"
- ❌ "Sidebar collapses"

### What TO test (Product Behavior):

- ✅ "Selecting an LLM provider configures the agent to use that provider"
- ✅ "Creating a new agent persists it and shows in the agents list"
- ✅ "Running a tool with parameters returns the expected output"
- ✅ "Chat messages stream correctly and maintain conversation context"
- ✅ "Workflow execution triggers tools in the correct order"

## BDD Structure (REQUIRED)

**Every E2E spec MUST follow the same BDD shape as the MSW tests.** In `packages/playground`, `e2e-bdd/test-needs-when-describe` enforces this shape.

The structure has exactly three levels:

1. **Outer `test.describe`** = the unit under test (one page or feature per file).
2. **Inner `test.describe('when ...')`** = exactly ONE precondition. The title MUST start with `when`.
3. **Each `test`** = exactly ONE observable outcome.

```ts
import { test, expect } from '@playwright/test';
import { resetStorage } from '../__utils__/reset-storage';

test.describe('Tools list page', () => {
  // the unit
  test.afterEach(async () => {
    await resetStorage();
  });

  test.describe('when a registered tool is clicked', () => {
    // ONE precondition (starts with "when")
    test('navigates to that tool detail page', async ({ page }) => {
      // ONE outcome
      await page.goto('/tools');
      await page.locator('text=Get current weather for a location').click();
      await expect(page).toHaveURL(/\/tools\/weatherInfo$/);
    });

    test('shows the tool name as the page heading', async ({ page }) => {
      // ONE outcome
      await page.goto('/tools');
      await page.locator('text=Get current weather for a location').click();
      await expect(page.locator('h2')).toHaveText('weatherInfo');
    });
  });
});
```

Rules:

- One outer `test.describe` per file naming the unit.
- Every leaf `test` lives inside a `test.describe('when ...')` precondition group. **No top-level flat `test()`.**
- Split a multi-assertion `test()` only where assertions represent **distinct outcomes**; keep tightly-coupled assertions that prove a single outcome together. Never drop an assertion.
- Place `beforeEach`/`afterEach` in the narrowest `describe` scope that needs them.

## Prerequisites

Requires Playwright MCP server. If the `browser_navigate` tool is unavailable, instruct the user to add it:

```sh
claude mcp add playwright -- npx @playwright/mcp@latest
```

## Step 1: Understand the Feature Intent

Before writing ANY test, answer these questions:

1. **What user problem does this feature solve?**
2. **What is the expected outcome when the feature works correctly?**
3. **What data flows through the system?** (user input → API → state → UI)
4. **What should persist after page reload?**
5. **What downstream effects should this action have?**

Document these answers as comments in your test file.

## Step 2: Build and Start

```sh
pnpm build:cli
cd packages/playground/e2e/kitchen-sink && pnpm dev
```

Verify server at http://localhost:4111

## Step 3: Map Feature to Behavior Tests

### Feature-to-Test Mapping Guide

| Feature Category           | What to Test                                      | Example Assertion                                            |
| -------------------------- | ------------------------------------------------- | ------------------------------------------------------------ |
| **Agent Configuration**    | Config changes affect agent behavior              | Send message → verify response uses selected model           |
| **LLM Provider Selection** | Selected provider is used in requests             | Intercept API call → verify provider in request payload      |
| **Tool Execution**         | Tool runs with correct params & returns result    | Execute tool → verify output matches expected transformation |
| **Workflow Execution**     | Steps execute in order, data flows between steps  | Run workflow → verify each step's output feeds next step     |
| **Chat/Streaming**         | Messages persist, context maintained across turns | Multi-turn conversation → verify context awareness           |
| **MCP Server Tools**       | Server tools are callable and return data         | Call MCP tool → verify response structure and content        |
| **Memory/Persistence**     | Data survives page reload                         | Create item → reload → verify item exists                    |
| **Error Handling**         | Errors surface correctly to user                  | Trigger error condition → verify error message + recovery    |

## Step 4: Write Behavior-Focused Tests

### Test Structure Template

```ts
import { test, expect, Page } from '@playwright/test';
import { resetStorage } from '../__utils__/reset-storage';
import { selectFixture } from '../__utils__/select-fixture';
import { nanoid } from 'nanoid';

/**
 * FEATURE: [Name of feature]
 * USER STORY: As a user, I want to [action] so that [outcome]
 * BEHAVIOR UNDER TEST: [Specific behavior being validated]
 */

test.describe('[Feature Name] - Behavior Tests', () => {
  let page: Page;

  test.beforeEach(async ({ browser }) => {
    const context = await browser.newContext();
    page = await context.newPage();
  });

  test.afterEach(async () => {
 

CAUTIONgrade B · trust 89/100 Install with care. The audit found things worth knowing before you trust its output.

What the source does

Filesystem

none-observed

Network

declared (1 observation(s))

Shell

none-observed

Dependencies

pinned

Secrets in source

none-found

Findings (5)

.claude/commands/changeset.md

.claude/commands/commit.md

.claude/commands/critique-pr.md

.claude/commands/document.md

.claude/commands/gh-bulk-issues.md

Gates applied: no_behavioural_pass.

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