mock an event emitter with sinon in javascript

To mock an event emitter with sinon, you can create a fake implementation of the event emitter using sinon.stub(). Here's an example:

index.tsx
const sinon = require('sinon');
const EventEmitter = require('events');

// Create a fake event emitter using sinon
const fakeEmitter = sinon.createStubInstance(EventEmitter);

// Define behavior for the event emitter
fakeEmitter.emit.withArgs('myEvent').returns('hello world');

// Trigger the event and assert that the behavior was executed
fakeEmitter.emit('myEvent'); // returns 'hello world'
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In this example, we create a fake implementation of the EventEmitter class using sinon.createStubInstance(). We then define the behavior of the emit() method using fakeEmitter.emit.withArgs() and returns(). Finally, we trigger the event using fakeEmitter.emit() and assert that the behavior was executed correctly.

Note that we only defined the behavior for the 'myEvent' event in this example, but you can define as many events as needed using fakeEmitter.emit.withArgs() and returns() statements.