Cohere Local Dev Loop

Overview

Set up a fast, reproducible local development workflow with Cohere API v2 mocking, vitest testing, and hot reload.

Prerequisites

Completed cohere-install-auth setup
Node.js 18+ with npm/pnpm
TypeScript project with tsx or ts-node

Instructions

Step 1: Project Structure

my-cohere-project/
├── src/
│   ├── cohere/
│   │   ├── client.ts       # CohereClientV2 wrapper
│   │   ├── chat.ts         # Chat completions
│   │   ├── embed.ts        # Embedding operations
│   │   └── rerank.ts       # Reranking operations
│   └── index.ts
├── tests/
│   ├── chat.test.ts
│   ├── embed.test.ts
│   └── fixtures/
│       └── responses.ts    # Mock API responses
├── .env.local              # Local secrets (git-ignored)
├── .env.example            # Template for team
└── package.json

Step 2: Package Setup

{
  "scripts": {
    "dev": "tsx watch src/index.ts",
    "test": "vitest",
    "test:watch": "vitest --watch",
    "test:integration": "COHERE_INTEGRATION=1 vitest --run"
  },
  "dependencies": {
    "cohere-ai": "^7.0.0"
  },
  "devDependencies": {
    "tsx": "^4.0.0",
    "vitest": "^2.0.0",
    "typescript": "^5.5.0"
  }
}

Step 3: Client Wrapper

// src/cohere/client.ts
import { CohereClientV2 } from 'cohere-ai';

let instance: CohereClientV2 | null = null;

export function getCohere(): CohereClientV2 {
  if (!instance) {
    instance = new CohereClientV2({
      token: process.env.CO_API_KEY,
    });
  }
  return instance;
}

// Reset for testing
export function resetClient(): void {
  instance = null;
}

Step 4: Mock Fixtures

// tests/fixtures/responses.ts
export const mockChatResponse = {
  id: 'test-chat-id',
  message: {
    role: 'assistant' as const,
    content: [{ type: 'text' as const, text: 'Mocked response' }],
  },
  finishReason: 'COMPLETE' as const,
  usage: { billedUnits: { inputTokens: 10, outputTokens: 5 } },
};

export const mockEmbedResponse = {
  id: 'test-embed-id',
  embeddings: {
    float: [[0.1, 0.2, 0.3, 0.4]], // truncated for dev
  },
  meta: { billedUnits: { inputTokens: 4 } },
};

export const mockRerankResponse = {
  id: 'test-rerank-id',
  results: [
    { index: 0, relevanceScore: 0.95 },
    { index: 2, relevanceScore: 0.72 },
  ],
  meta: { billedUnits: { searchUnits: 1 } },
};

Step 5: Test with Mocks

// tests/chat.test.ts
import { describe, it, expect, vi, beforeEach } from 'vitest';
import { mockChatResponse } from './fixtures/responses';

vi.mock('cohere-ai', () => ({
  CohereClientV2: vi.fn().mockImplementation(() => ({
    chat: vi.fn().mockResolvedValue(mockChatResponse),
    chatStream: vi.fn().mockReturnValue({
      [Symbol.asyncIterator]: async function* () {
        yield { type: 'content-delta', delta: { message: { content: { text: 'Hi' } } } };
      },
    }),
    embed: vi.fn().mockResolvedValue({ embeddings: { float: [[0.1, 0.2]] } }),
    rerank: vi.fn().mockResolvedValue({
      results: [{ index: 0, relevanceScore: 0.9 }],
    }),
  })),
}));

describe('Cohere Chat', () => {
  it('should return a chat completion', async () => {
    const { CohereClientV2 } = await import('cohere-ai');
    const cohere = new CohereClientV2();

    const result = await cohere.chat({
      model: 'command-a-03-2025',
      messages: [{ role: 'user', content: 'test' }],
    });

    expect(result.message?.content?.[0]?.text).toBe('Mocked response');
    expect(result.finishReason).toBe('COMPLETE');
  });
});

Step 6: Integration Tests (Optional, Hits Real API)

// tests/integration.test.ts
import { describe, it, expect } from 'vitest';
import { CohereClientV2 } from 'cohere-ai';

const shouldRun = process.env.COHERE_INTEGRATION === '1';

describe.skipIf(!shouldRun)('Cohere Integration', () => {
  const cohere = new CohereClientV2();

  it('chat endpoint responds', async () => {
    const res = await cohere.chat({
      model: 'command-r7b-12-2024', // cheapest model for tests
      messages: [{ role: 'user', content: 'Say OK' }],
      maxTokens: 5,
    });
    expect(res.message?.content?.[0]?.text).toBeTruthy();
  }, 15_000);

  it('embed endpoint responds', async () => {
    const res = await cohere.embed({
      model: 'embed-v4.0',
      texts: ['test'],
      inputType: 'search_document',
      embeddingTypes: ['float'],
    });
    expect(res.embeddings.float[0].length).toBeGreaterThan(0);
  }, 15_000);
});

Environment Management

# .env.example (commit this)
CO_API_KEY=your-trial-key-here

# .env.local (git-ignored, used by tsx/vitest)
CO_API_KEY=actual-key

# .gitignore entries
.env.local
.env.*.local

Output

Working dev environment with hot reload via tsx watch
Unit tests with mocked Cohere responses (no API calls)
Optional integration tests gated by COHERE_INTEGRATION=1
Mock fixtures matching real API v2 response shapes

Error Handling

Error	Cause	Solution
`vi.mock not working`	Wrong import order	Mock before importing modules
`CO_API_KEY undefined`	.env not loaded	Use `dotenv/config` or tsx env support
Integration test timeout	Slow network	Increase timeout to 15s+
Type mismatch on mock	API shape changed	Update fixtures to match SDK types

Examples

Run unit tests with a mocked v2 chat response and assert that no credential or network call is needed, then enable one integration test only in the isolated staging environment. If fixture and SDK shapes diverge, update the sanitized fixture and contract assertion before allowing application changes to merge.

Resources

Next Steps

See cohere-sdk-patterns for production-ready code patterns.