Mistral AI Local Dev Loop

Overview

Set up a fast, reproducible local development workflow for Mistral AI integrations: project scaffold, environment config, hot reload with tsx, unit tests with Vitest mocking, and integration tests against the live API.

Prerequisites

• Completed mistral-install-auth setup
• Node.js 18+ with npm/pnpm
• MISTRALAPIKEY set in environment

Instructions

Step 1: Project Structure

my-mistral-project/
├── src/
│   ├── mistral/
│   │   ├── client.ts       # Singleton client
│   │   ├── config.ts       # Config with Zod validation
│   │   └── types.ts        # TypeScript types
│   └── index.ts
├── tests/
│   ├── unit/
│   │   └── mistral.test.ts
│   └── integration/
│       └── mistral.integration.test.ts
├── .env.local              # Local secrets (git-ignored)
├── .env.example            # Template for team
├── tsconfig.json
├── vitest.config.ts
└── package.json

Step 2: Package Configuration

package.json

{
  "type": "module",
  "scripts": {
    "dev": "tsx watch src/index.ts",
    "build": "tsc",
    "test": "vitest run",
    "test:watch": "vitest",
    "test:integration": "vitest run tests/integration/",
    "typecheck": "tsc --noEmit"
  },
  "dependencies": {
    "@mistralai/mistralai": "^1.0.0"
  },
  "devDependencies": {
    "@types/node": "^20.0.0",
    "dotenv": "^16.0.0",
    "tsx": "^4.0.0",
    "typescript": "^5.0.0",
    "vitest": "^1.0.0"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "outDir": "dist",
    "rootDir": "src"
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules", "dist"]
}

Step 3: Environment Setup

# Create environment template
cat > .env.example << 'EOF'
MISTRAL_API_KEY=your-api-key-here
MISTRAL_MODEL=mistral-small-latest
LOG_LEVEL=debug
EOF

cp .env.example .env.local
echo '.env.local' >> .gitignore
echo '.env' >> .gitignore

Step 4: Client Module

// src/mistral/client.ts
import { Mistral } from '@mistralai/mistralai';
import 'dotenv/config';

let instance: Mistral | null = null;

export function getMistralClient(): Mistral {
  if (!instance) {
    const apiKey = process.env.MISTRAL_API_KEY;
    if (!apiKey) throw new Error('MISTRAL_API_KEY not set');
    instance = new Mistral({ apiKey, timeoutMs: 30_000 });
  }
  return instance;
}

export function resetClient(): void {
  instance = null;
}

Step 5: Unit Tests with Mocking

vitest.config.ts

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    globals: true,
    environment: 'node',
    include: ['tests/**/*.test.ts'],
    coverage: { provider: 'v8', reporter: ['text', 'json'] },
  },
});

tests/unit/mistral.test.ts

import { describe, it, expect, vi, beforeEach } from 'vitest';

// Mock the entire SDK
vi.mock('@mistralai/mistralai', () => ({
  Mistral: vi.fn().mockImplementation(() => ({
    chat: {
      complete: vi.fn().mockResolvedValue({
        id: 'test-id',
        model: 'mistral-small-latest',
        choices: [{
          index: 0,
          message: { role: 'assistant', content: 'Mocked response' },
          finishReason: 'stop',
        }],
        usage: { promptTokens: 10, completionTokens: 5, totalTokens: 15 },
      }),
      stream: vi.fn().mockImplementation(async function* () {
        yield { data: { choices: [{ delta: { content: 'Streamed ' } }] } };
        yield { data: { choices: [{ delta: { content: 'response' } }] } };
      }),
    },
    embeddings: {
      create: vi.fn().mockResolvedValue({
        data: [{ embedding: new Array(1024).fill(0.1) }],
        usage: { totalTokens: 5 },
      }),
    },
    models: {
      list: vi.fn().mockResolvedValue({ data: [{ id: 'mistral-small-latest' }] }),
    },
  })),
}));

describe('Mistral Client', () => {
  beforeEach(() => { vi.clearAllMocks(); });

  it('should complete chat', async () => {
    const { Mistral } = await import('@mistralai/mistralai');
    const client = new Mistral({ apiKey: 'test' });

    const response = await client.chat.complete({
      model: 'mistral-small-latest',
      messages: [{ role: 'user', content: 'Test' }],
    });

    expect(response.choices?.[0]?.message?.content).toBe('Mocked response');
    expect(response.usage?.totalTokens).toBe(15);
  });

  it('should generate embeddings', async () => {
    const { Mistral } = await import('@mistralai/mistralai');
    const client = new Mistral({ apiKey: 'test' });

    const response = await client.embeddings.create({
      model: 'mistral-embed',
      inputs: ['test text'],
    });

    expect(response.data[0].embedding).toHaveLength(1024);
  });
});

Step 6: Integration Test (Live API)

// tests/integration/mistral.integration.test.ts
import { describe, it, expect } from 'vitest';
import { Mistral } from '@mistralai/mistralai';

const apiKey = process.env.MISTRAL_API_KEY;

describe.skipIf(!apiKey)('Mistral Integration', () => {
  const client = new Mistral({ apiKey: apiKey! });

  it('should list models', async () => {
    const models = await client.models.list();
    expect(models.data?.length).toBeGreaterThan(0);
  }, 10_000);

  it('should complete chat', async () => {
    const response = await client.chat.complete({
      model: 'mistral-small-latest',
      messages: [{ role: 'user', content: 'Reply with "ok"' }],
      maxTokens: 10,
      temperature: 0,
    });
    expect(response.choices?.[0]?.message?.content).toBeTruthy();
  }, 15_000);

  it('should generate embeddings', async () => {
    const response = await client.embeddings.create({
      model: 'mistral-embed',
      inputs: ['test'],
    });
    expect(response.data[0].embedding).toHaveLength(1024);
  }, 10_000);
});

Output

• Working dev environment with hot reload (tsx watch)
• Unit tests with full SDK mocking
• Integration tests against live API (skip when no key)
• Environment variable management with .env.local

Error Handling

Resources

• Mistral TypeScript SDK
• Vitest Documentation
• tsx

Next Steps

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