WireMock Standalone Docker Skill

Overview

Provides patterns for running WireMock as a standalone Docker container to mock external APIs during integration and end-to-end testing. Runs WireMock as a separate service that simulates real API behavior for testing HTTP clients, retry logic, and error handling.

When to Use

Use when you need to:

• Mock external APIs during integration or end-to-end testing
• Simulate error conditions (timeouts, 5xx, rate limiting) without real services
• Test HTTP client configurations, retry logic, and error handling
• Create portable, reproducible test environments
• Validate API contracts before implementing the real service

Instructions

Step 1: Set Up Docker Compose

Create a docker-compose.yml with WireMock 3.5.2, port mapping, and volume mounts for mappings and files:

version: "3.8"
services:
  wiremock:
    image: wiremock/wiremock:3.5.2
    ports:
      - "8080:8080"
    volumes:
      - ./wiremock:/home/wiremock
    command: ["--global-response-templating"]

Step 2: Create Directory Structure

Create the WireMock configuration directories:

wiremock/
├── mappings/   # JSON stub definitions
└── __files/   # Response body files

Step 3: Define API Mappings

Create JSON stub files in wiremock/mappings/ for each scenario:

• Success: Return 200 with JSON body
• Not Found: Return 404
• Server Error: Return 500
• Timeout: Use fixedDelayMilliseconds
• Rate Limit: Return 429 with Retry-After header

Step 4: Start WireMock

docker compose up -d

Step 5: Verify WireMock is Running

curl http://localhost:8080/__admin/mappings

Expected: Returns empty array {"mappings":[]} if no stubs loaded, or your stub definitions. If you get connection refused, check that the container is running: docker compose ps

Step 6: Configure HTTP Client

Point your application to http://localhost:8080 (or http://wiremock:8080 in Docker network) instead of the real API.

Step 7: Test Edge Cases

Always test: 200, 400, 401, 403, 404, 429, 500, timeouts, malformed responses.

Examples

Example 1: Mock Successful GET Request

{
  "request": { "method": "GET", "url": "/api/users/123" },
  "response": {
    "status": 200,
    "jsonBody": { "id": 123, "name": "Mario Rossi" }
  }
}

Example 2: Mock Server Error

{
  "request": { "method": "GET", "url": "/api/error" },
  "response": { "status": 500, "body": "Internal Server Error" }
}

Example 3: Mock Timeout

{
  "request": { "method": "GET", "url": "/api/slow" },
  "response": {
    "status": 200,
    "fixedDelayMilliseconds": 5000,
    "jsonBody": { "message": "delayed" }
  }
}

Example 4: Docker Compose with Application

services:
  wiremock:
    image: wiremock/wiremock:3.5.2
    ports:
      - "8080:8080"
    volumes:

  - ./wiremock:/home/wiremock

## Best Practices

1. **Organize mappings by feature**: Use subdirectories like `users/`, `products/`
2. **Version control mappings**: Keep mappings in git for reproducible tests
3. **Test all error scenarios**: 401, 403, 404, 429, 500, timeouts
4. **Reset between test runs**: `curl -X POST http://localhost:8080/__admin/reset`
5. **Use descriptive file names**: `get-user-success.json`, `post-user-error.json`

## Constraints and Warnings

- Ensure port 8080 is available or map to a different port
- Configure Docker networking when running multiple containers
- Enable `--global-response-templating` for dynamic responses
- WireMock resets mappings on container restart

## Troubleshooting

**Requests don't match stubs?**
Check what WireMock received: `curl http://localhost:8080/__admin/requests` — shows unmatched requests with details about what was actually sent.

**Stub file not loading?**
Verify file location: place JSON stubs in `wiremock/mappings/` and response files in `wiremock/__files/`. Check file permissions.

**Connection refused errors?**
Run `docker compose ps` to verify the container is running. Check port conflicts with `lsof -i :8080`.

## References

See `references/` for complete examples:
- `docker-compose.yml` - Full Docker Compose configuration
- `wiremock/mappings/` - Complete stub examples for all scenarios