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@youzi9601/mcp-testkit-vitest

Vitest integration plugin, auto-registers MCP-specific custom matchers.

Installation

npm install -D @youzi9601/mcp-testkit-vitest vitest@4

Setup

// vitest.config.ts
import { defineConfig } from 'vitest/config'
import mcpTestkit from '@youzi9601/mcp-testkit-vitest'

export default defineConfig({
  plugins: [mcpTestkit()],
  test: {
    environment: 'node',
  },
})

One line — the plugin auto-registers these matchers to Vitest's expect():

Matcher	Description
expect(value).toBeValidMcpResponse()	Valid MCP JSON-RPC response
expect(value).toBeMcpSuccess()	Success response with result
expect(value).toBeMcpError(code?)	Error response, optionally with specific code
expect(value).toBeValidJsonRpcRequest()	Well-formed JSON-RPC request

Example

import { createMcpServer } from '@youzi9601/mcp-testkit'

describe('MCP Server Tests', () => {
  let server: Awaited<ReturnType<typeof createMcpServer>>

  beforeEach(async () => {
    server = await createMcpServer({
      command: 'node',
      args: ['./dist/server.js'],
    })
  })

  afterEach(() => server.close())

  it('should return valid MCP response', async () => {
    const result = await server.callTool('echo', { msg: 'hello' })
    expect(result).toBeValidMcpResponse()
    expect(result).toBeMcpSuccess()
  })

  it('should handle error responses', async () => {
    const result = await server.callTool('invalidTool', {})
    expect(result).toBeMcpError(-32601) // MethodNotFound
  })
})

Relationship with @youzi9601/mcp-testkit

• mcpTestkit() is the accompanying package for @youzi9601/mcp-testkit
• Core logic, types, and error classes live in mcp-testkit
• This package only handles Vitest integration

License

MIT