Testing AI Agents in TypeScript: Unit Tests, Mocks & Integration Testing

1import { describe, it, expect, vi } from 'vitest';
2import { createAgent } from 'smoke-monkey-harness';
3
4// Mock the LLM provider to return a scripted tool call sequence
5vi.mock('smoke-monkey-harness/providers', () => ({
6  createProvider: () => ({
7    complete: vi.fn()
8      // First call: agent decides to read a file
9      .mockResolvedValueOnce({
10        toolCalls: [{ name: 'read_file', args: { path: 'src/utils.ts' } }],
11      })
12      // Second call: agent writes the fix
13      .mockResolvedValueOnce({
14        toolCalls: [{ name: 'replace_file_content', args: {
15          path: 'src/utils.ts',
16          oldText: 'var x = 1',
17          newText: 'const x = 1',
18        }}],
19      })
20      // Third call: agent completes
21      .mockResolvedValueOnce({ content: 'Done. Replaced var with const.' }),
22  }),
23}));
24
25describe('refactoring agent', () => {
26  it('replaces var with const in target file', async () => {
27    const agent = createAgent({ provider: 'anthropic', model: 'claude-3-7-sonnet', workspacePath: '/tmp/test' });
28    const result = await agent.run('Replace all var declarations with const');
29    expect(result.toolCallCount).toBe(2);
30    expect(result.summary).toContain('const');
31  });
32});