How can you easily tell if TypeScript code is being executed in a Jasmine/Karma test environment?

In my situation, there exists a static method that generates an object with service-like functionality, which can be accessed through another static method. Here is an example:

expect class FooService {
   private static instance : FooService;
   static getInstance() {
        if (!this.instance) {
           this.instance = new FooService();
        }
        return this.instance
  private constructor() {}
  [implementation]

}

The issue at hand is determining whether the `getInstance()` method is being called within my Angular application or during a unit test. This distinction would enable me to return either a mock version of the object or the real one.

This is what I envision:

 expect class FooService {
   private static instance : FooService;
   static getInstance() {
       if (isInJasmineTest()} {              <----
           return new MockFooService() 
       } 
       if (!this.instance) {
           this.instance = new FooService();
       }
       return this.instance
   }
   private constructor() {}
   [implementation]

}

While I acknowledge that there are various techniques involving spys, mocks, and injection to accomplish this task,

I am particularly interested in understanding how to incorporate isInJasmineTest()?

One approach might involve designing a function that gets invoked in the `beforeAll` section of each Jasmine test, such as `setJasmineTestEnvironment(true)`. However, I am curious if there is already an existing mechanism available for inspection without necessitating the creation of an additional function like this.

Answer №1

If you are running tests using Karma, there are a few tips that could be beneficial.

Because Karma injects elements into the DOM for testing purposes, it is possible to search for these injected elements.

For example,

document.getElementById('banner');
is injected at the top of the body and displays the Karma banner that appears above all HTML test output.

Additionally,

const isKarma = document.getElementsByTagName("title")[0].innerHTML === 'Karma';

Karma changes the page title to its own name, so verifying this can also be a useful approach.

To access the DOM in Angular, injection is necessary:

import { Injectable, Inject } from '@angular/core';
// We import DOCUMENT from @angular/common.
import { DOCUMENT } from '@angular/common';

constructor(@Inject(DOCUMENT) private document: HTMLDocument){}

Once this setup is complete, you can interact with this.document as you would with the regular document object in an Angular component.

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