jest-runtime

Module Mocking

Allows you to mock modules to isolate your tests from their dependencies, providing a way to test modules in isolation.

jest.mock('moduleName');

Test Environment Setup

Enables you to programmatically create a test environment, including the haste map (module map) and the test runner, which can be used to execute test files.

const runtime = require('jest-runtime');
// Create a runtime to execute the test
runtime.createHasteMap(config).then(hasteMap => {
  const environment = new runtime.TestEnvironment(config);
  const runner = new runtime.TestRunner(environment, hasteMap.resolver);
  // Execute the test file
  runner.runTest(filePath);
});

Script Transformation

Provides the ability to transform scripts using Jest's built-in transformers or custom ones. This is useful for preprocessing files before they are executed in the test environment.

const runtime = require('jest-runtime');
// Create a new runtime instance
const jestRuntime = new runtime.ScriptTransformer(config);
// Transform a script
const transformedCode = jestRuntime.transformSource(filePath, fileContent, false);