fix(ssr): resolve EventSource SSR violations and implement best practices
- Fix EventSource is not defined error in queue dashboard - Add browser guards for all EventSource usage - Replace static constants (EventSource.OPEN/CLOSED) with numeric values - Fix setInterval SSR violation in LLM health indicator - Replace $effect anti-pattern with onMount in share page - Add comprehensive SvelteKit SSR best practices documentation - Add SSR audit and testing verification All changes follow SvelteKit best practices and are verified against official documentation. Production build succeeds with no SSR errors. Closes: FixEventSourceSSR See: docs/outcomes/FixEventSourceSSR.md
This commit is contained in:
Giancarmine Salucci
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docs/TESTING.md
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docs/TESTING.md
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# Vitest Mocking Guide for SvelteKit
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This guide explains how to properly mock dependencies when testing SvelteKit applications with Vitest.
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## Understanding Mocking in SvelteKit Context
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SvelteKit has a unique architecture where code can run on both server and client. This affects how we mock:
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1. **Server-only modules** (`$lib/server/*`, `*.server.ts`) - Only run on server
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2. **Universal modules** - Can run on both server and client
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3. **Environment variables** - Different modules for static vs dynamic access
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## Key Principles
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1. **`vi.mock()` is hoisted** - Always executed before imports
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2. **Use factory functions** - Return mocked implementations
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3. **Mock before import** - Mocks must be defined before the module is imported
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4. **Clean up** - Always restore/reset mocks in `beforeEach` or `afterEach`
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---
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## Mocking Environment Variables ($env/dynamic/private)
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**Problem:** Can't directly mock `$env/dynamic/private` because it's a SvelteKit magic module.
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**Solution:** Create a config module that wraps env access, then mock the config.
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### Example: Queue Config Module
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```typescript
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// src/lib/server/queue/config.ts
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import { env } from '$env/dynamic/private';
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export const queueConfig = {
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concurrency: parseInt(env.QUEUE_CONCURRENCY || '2', 10),
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maxRetries: parseInt(env.QUEUE_MAX_RETRIES || '3', 10),
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tandoor: {
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enabled: !!env.TANDOOR_TOKEN,
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token: env.TANDOOR_TOKEN || null
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}
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};
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```
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### Mocking the Config in Tests
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```typescript
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import { vi, beforeEach, afterEach } from 'vitest';
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import * as queueConfigModule from '$lib/server/queue/config';
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// Mock the config module
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vi.mock('$lib/server/queue/config', () => ({
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queueConfig: {
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concurrency: 2,
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maxRetries: 3,
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tandoor: { enabled: true, token: 'test-token' }
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}
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}));
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describe('QueueProcessor', () => {
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beforeEach(() => {
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vi.clearAllMocks();
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});
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afterEach(() => {
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vi.restoreAllMocks();
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});
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});
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```
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---
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## Mocking External Service Modules
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### Recommended Approach: Mock Entire Module
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```typescript
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import { vi } from 'vitest';
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// IMPORTANT: Mock BEFORE importing the module that uses it
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vi.mock('$lib/server/extraction', () => ({
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extractTextAndThumbnail: vi.fn().mockResolvedValue({
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bodyText: 'Mock recipe text',
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thumbnail: 'https://mock.com/image.jpg'
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})
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}));
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// NOW import the module that depends on these
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import { queueProcessor } from '$lib/server/queue/QueueProcessor';
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import { extractTextAndThumbnail } from '$lib/server/extraction';
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describe('QueueProcessor', () => {
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it('should use mocked services', async () => {
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const item = queueManager.enqueue('https://instagram.com/p/test');
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// Verify mock was called
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expect(extractTextAndThumbnail).toHaveBeenCalledWith(
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'https://instagram.com/p/test',
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expect.any(Function)
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);
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});
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});
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```
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---
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## Mocking API Endpoints (SvelteKit RequestHandler)
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When testing API endpoints, be aware that error responses must be properly awaited:
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```typescript
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import { describe, it, expect } from 'vitest';
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import { POST } from '../routes/api/queue/+server';
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describe('POST /api/queue', () => {
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it('should reject invalid URLs', async () => {
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const request = new Request('http://localhost/api/queue', {
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method: 'POST',
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headers: { 'Content-Type': 'application/json' },
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body: JSON.stringify({ url: 'invalid-url' })
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});
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const response = await POST({ request } as any);
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// ✅ CORRECT - Check status first
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expect(response.status).toBe(400);
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// ✅ CORRECT - Properly await error response
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const data = await response.json();
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expect(data.message).toContain('Invalid');
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});
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});
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```
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### Common Pitfall: Not Awaiting Error Responses
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```typescript
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// ❌ WRONG - This will fail
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it('should reject invalid input', async () => {
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const response = await endpoint({ request } as any);
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const data = response.json(); // Missing await!
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expect(data.message).toBe('Error'); // data is a Promise
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});
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// ✅ CORRECT
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it('should reject invalid input', async () => {
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const response = await endpoint({ request } as any);
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expect(response.status).toBe(400);
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const data = await response.json(); // Properly awaited
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expect(data.message).toBe('Error');
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});
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```
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---
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## Common Pitfalls and Solutions
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### Problem 1: Mock Not Working
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```typescript
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// ❌ WRONG - Import before mock
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import { queueProcessor } from './QueueProcessor';
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vi.mock('./extraction');
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// ✅ CORRECT - Mock before import
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vi.mock('./extraction');
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import { queueProcessor } from './QueueProcessor';
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```
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### Problem 2: Mocks Not Resetting Between Tests
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```typescript
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// ✅ SOLUTION - Always clean up
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import { beforeEach, afterEach } from 'vitest';
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beforeEach(() => {
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vi.clearAllMocks(); // Clear call history
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});
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afterEach(() => {
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vi.restoreAllMocks(); // Restore original implementations
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});
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```
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### Problem 3: TypeScript Errors with Mocked Functions
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```typescript
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import { vi } from 'vitest';
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// ✅ CORRECT - Type assertion
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const mockFn = vi.fn<() => Promise<string>>();
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mockFn.mockResolvedValue('test');
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// OR use vi.mocked()
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import { vi, type Mock } from 'vitest';
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const mockFn = vi.fn() as Mock<() => Promise<string>>;
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```
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---
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## Testing Async Queue Processing
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### Solution 1: Wait for Processing
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```typescript
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it('should process item', async () => {
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const item = queueManager.enqueue('https://instagram.com/p/test');
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// Wait for processing with timeout
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await vi.waitFor(
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() => {
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const updated = queueManager.get(item.id);
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expect(updated?.status).toBe('success');
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},
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{ timeout: 5000, interval: 100 }
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);
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});
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```
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### Solution 2: Use Fake Timers
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```typescript
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import { vi } from 'vitest';
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beforeEach(() => {
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vi.useFakeTimers();
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});
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afterEach(() => {
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vi.useRealTimers();
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});
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it('should process after delay', async () => {
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queueManager.enqueue('https://test.com');
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// Fast-forward time
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await vi.advanceTimersByTimeAsync(1000);
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// Now check results
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});
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```
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---
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## Best Practices for SvelteKit + Vitest
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1. **Always mock before import** - `vi.mock()` calls are hoisted but still need to be before your imports
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2. **Use factory functions** - Return new instances to avoid state leaking between tests
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3. **Clean up thoroughly** - Use `beforeEach`/`afterEach` to reset state
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4. **Type your mocks** - Use TypeScript generics for type-safe mocks
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5. **Test isolation** - Each test should be independent
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6. **Mock at the right level** - Mock external boundaries (HTTP, DB), not internal logic
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7. **Use `vi.waitFor()`** - For async operations instead of arbitrary `setTimeout()`
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8. **Snapshot complex mocks** - Use `expect.any(Function)` for callbacks
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9. **Always await `.json()` on responses** - Both success and error responses
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---
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## Quick Reference: Mock Cheat Sheet
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```typescript
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// Mock entire module
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vi.mock('./module', () => ({ export: vi.fn() }));
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// Mock with factory
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vi.mock('./module', () => {
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return { dynamicExport: () => 'value' };
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});
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// Spy on existing export
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vi.spyOn(module, 'export').mockReturnValue('value');
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// Mock return value
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mockFn.mockReturnValue('sync value');
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mockFn.mockResolvedValue('async value');
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mockFn.mockRejectedValue(new Error('async error'));
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// Mock implementation
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mockFn.mockImplementation((arg) => arg * 2);
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mockFn.mockImplementationOnce((arg) => arg * 3);
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// Check calls
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expect(mockFn).toHaveBeenCalled();
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expect(mockFn).toHaveBeenCalledTimes(2);
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expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2');
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expect(mockFn).toHaveBeenLastCalledWith('arg');
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// Reset/restore
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vi.clearAllMocks(); // Clear call history
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vi.resetAllMocks(); // + Reset implementations
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vi.restoreAllMocks(); // + Restore original implementations
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// Environment variables
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vi.stubEnv('VAR_NAME', 'value');
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vi.unstubAllEnvs();
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// Timers
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vi.useFakeTimers();
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vi.advanceTimersByTime(1000);
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await vi.advanceTimersByTimeAsync(1000);
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vi.useRealTimers();
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// Async helpers
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await vi.waitFor(() => expect(condition).toBe(true));
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await vi.waitUntil(() => condition === true);
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```
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---
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## Examples from This Project
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See the following test files for real-world examples:
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- `src/tests/queue-manager.spec.ts` - Mocking external services
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- `src/tests/queue-processor.spec.ts` - Mocking config module and services
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- `src/tests/queue-api.spec.ts` - Testing API endpoints with proper async handling
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---
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## Additional Resources
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- [Vitest Mocking Guide](https://vitest.dev/guide/mocking.html)
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- [SvelteKit Testing](https://kit.svelte.dev/docs/testing)
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- [Vitest API Reference](https://vitest.dev/api/)
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