sinon

import sinon from 'sinon'; // Simulate an external API dependency class ExternalAPI { async getData(): Promise<string> { // In a real application, this would make an actual network call return Promise.resolve('Real Data From Server'); } } // Our code under test that depends on ExternalAPI class MyService { constructor(private api: ExternalAPI) {} async processData(): Promise<string> { const data = await this.api.getData(); return data.toUpperCase(); } } async function runExample() { const api = new ExternalAPI(); const service = new MyService(api); // Create a stub for the API's getData method const getDataStub = sinon.stub(api, 'getData'); // Configure the stub to return a predictable, mock value getDataStub.resolves('Mocked Data'); // Call the method under test, which now uses the stubbed getData const result = await service.processData(); console.log('Processed Result:', result); // Expected output: MOCKED DATA console.log('getData was called once:', getDataStub.calledOnce); // Expected output: true // Restore the original method to clean up after the test getDataStub.restore(); } runExample().catch(console.error);