Mastering TypeScript 3 - Third Edition

Asynchronous tests

The asynchronous nature of JavaScript—made popular by AJAX and jQuery—has always been one of the draw-cards of the language, and is the principal architecture behind Node-based applications. Let's take a quick look at an asynchronous class, and then describe how we should go about testing it. Consider the following TypeScript code:

class MockAsyncClass { 
    executeSlowFunction(success: (value: string) => void) { 
        setTimeout(() => { 
            success("success"); 
        }, 1000); 
    } 
}

This MockAsyncClass has a single function, named executeSlowFunction, which takes a function callback named success. Within the executeSlowFunction code, we are simulating an asynchronous call with the setTimeout function, and only calling the success callback ...