wheresrhys/fetch-mock
Fetch Mock
Fetch-mock is a testing utility designed to isolate application code from external network dependencies by intercepting and overriding outgoing traffic. It functions as a network request interceptor that captures calls made via the Fetch API, allowing developers to simulate server responses and verify application behavior without requiring a live backend infrastructure.
The library distinguishes itself through a unified interface that provides consistent network interception logic across diverse runtime environments, including browsers, service workers, and server-side platforms. By replacing the native fetch function with a proxy, it enables the definition of custom response payloads, status codes, and headers, while simultaneously maintaining a log of all intercepted requests for post-execution verification.
The tool supports a range of testing methodologies, including frontend unit testing and API integration testing. It provides a matching engine to evaluate outgoing requests against user-defined predicates and includes capabilities for asserting that specific requests were executed with the expected parameters, methods, and headers.
Features
- API Request Mocking - Intercepts Fetch API requests to simulate server responses and verify application behavior without a live backend.
- Network Request Interceptors - Captures and overrides HTTP traffic to ensure test suites remain fast, deterministic, and independent of live servers.
- API Integration Testing - Validates application behavior by simulating specific HTTP server responses and error conditions during integration tests.
- Request Verification - Asserts that applications trigger expected HTTP requests with correct parameters, methods, and headers during automated tests.
- Frontend Unit Testing - Enables frontend unit testing by intercepting network calls to isolate components from backend dependencies.
- Request Matching Engines - Evaluates outgoing requests against user-defined predicates to select the appropriate mock response.
- Environment Abstraction Layers - Decouples network interception logic from specific runtime environments like browsers, Node.js, and service workers.
- Cross-Environment Test Harnesses - Ensures consistent network interception behavior across diverse runtime environments including browsers and server-side platforms.
- Request Interception Middleware - Processes outgoing requests through a chain of handlers to determine whether to return a mock or proceed.
- Response Mocking - Allows configuration of custom response bodies, status codes, and headers to simulate various server outcomes.
- Network Request Histories - Maintains a detailed log of all intercepted network requests to enable post-execution verification and assertions.
- Cross-Environment Test Execution - Provides a consistent testing harness for network interception across browser and server-side JavaScript runtimes.
- Global Object Interception - Intercepts network calls by replacing the global fetch function with a proxy handler.
- JavaScript Testing Frameworks - Provides a library for isolating code from network dependencies during automated JavaScript test execution.
- Response Simulators - Provides asynchronous promise-based responses with custom headers and bodies to simulate network behavior during tests.
- Network Request Assertions - Validates application logic by asserting that specific network requests were made with the expected parameters and headers.
- Network Request Interception - Prevents actual network traffic during testing by capturing fetch calls and returning predefined responses.
