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

Examples

Separate deterministic and paid checks

Run the mocked Vitest suite on every local change and CI pull request. Enable the integration suite only in a protected environment that supplies MISTRALAPIKEY; it should skip—not fail—when that secret is intentionally absent from an untrusted pull request.

Resources

• Mistral TypeScript SDK
• Vitest Documentation
• tsx

Next Steps

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