Testing Patterns for Vercel AI SDK

Purpose: Provide comprehensive testing templates, mock providers, and testing strategies for Vercel AI SDK applications.

Activation Triggers:

• Writing tests for AI features
• Creating mock AI providers
• Testing streaming responses
• Testing tool calling functionality
• Implementing test coverage
• Snapshot testing for AI outputs

Key Resources:

• templates/mock-provider.ts - Mock language model implementation
• templates/streaming-test.ts - Test streaming responses
• templates/tool-calling-test.ts - Test tool execution
• templates/snapshot-test.ts - Snapshot testing for outputs
• scripts/generate-test-suite.sh - Generate test scaffolds
• scripts/run-coverage.sh - Run tests with coverage
• examples/ - Complete test suites for different features

Mock Provider Pattern

Template: templates/mock-provider.ts

import { createMockLanguageModelV1 } from 'ai/test'

const mockProvider = createMockLanguageModelV1({
  doGenerate: async ({ prompt, mode }) => ({
    text: 'Mocked response'
    finishReason: 'stop'
    usage: { promptTokens: 10, completionTokens: 20 }
  })
  doStream: async function* ({ prompt, mode }) {
    yield { type: 'text-delta', textDelta: 'Mocked ' }
    yield { type: 'text-delta', textDelta: 'streaming ' }
    yield { type: 'text-delta', textDelta: 'response' }
    yield {
      type: 'finish'
      finishReason: 'stop'
      usage: { promptTokens: 10, completionTokens: 20 }
    }
  }
})

Testing Strategies

1. Unit Tests (Mock Providers)

Test AI functions without real API calls

2. Integration Tests (Real Providers)

Test with real providers in CI (with rate limits)

3. Snapshot Tests

Ensure consistent outputs over time

4. E2E Tests

Test complete user flows with mocks

Test Coverage Goals

• Core Functions: >90%
• Error Handling: >80%
• Tool Calling: 100%
• Streaming: >85%

Resources

Templates:

• mock-provider.ts - Complete mock implementation
• streaming-test.ts - Streaming test patterns
• tool-calling-test.ts - Tool execution tests
• snapshot-test.ts - Snapshot testing setup

Scripts:

• generate-test-suite.sh - Scaffold tests
• run-coverage.sh - Run with coverage

Examples:

• complete-test-suite.test.ts - Full test suite example

Testing Frameworks: Vitest, Jest, Node Test Runner SDK Version: Vercel AI SDK 5+ Coverage Tool: c8, nyc, or built-in coverage

Best Practice: Use mock providers for fast, reliable tests