Unit testing static method that imports environment file

Question

I'm (very) new to writing unit tests and I'm wondering how I should approach testing a static method that constructs our API endpoints based on what the properties are set to in our environment.ts file.

The environment.ts file changes with the environment, so I'm curious how I would accommodate for that in my test.

Does my method need to be refactored to make this easier to test? For example, instead of implicitly referencing environment.endpoint, instead pass-in environment as a argument? Would I mock the environment.ts file?

Any suggestions would be helpful.

import {environment} from '../../environments/environment';

export class Utilities {

  public static constructAPIEndpoint(): string {
    const hostname: string = environment.endpoint;
    const protocol: string = environment.local ? 'http:' : 'https:';

    return `${protocol}//${hostname}/`;
  }
}

environments.ts

export const environment = {
  production: false,
  local: false,
  hostname: 'localhost',
  showLogs: true,
  endpoint: 'foo-dev-graphapp.com',
  appInsights: {
    instrumentationKey: '123'
  }
};

jasmine test:

  import {environment} from '../../environments/environment';

  it('constructAPIEndpoint() it should construct an endpoint based on environment.ts', () => {
    const endpoint: string = Utilities.constructAPIEndpoint();

    /// THIS DOESN'T SEEM - having to recreate logic inside constructAPIEndpoint()
    const protocol: string = environment.local ? 'http:' : 'https';


        expect(endpoint).toEqual(`${protocol}//${environment.endpoint}`);


  });

Answer 1

If you really want to unit test that logic, you should fake its data. In order to do that, you need a way to inject that dependency instead of getting it straight from it.

You have 3 options:

1. Installing a framework to mock the import (as detailed in https://medium.com/@emandm/import-mocking-with-typescript-3224804bb614)
2. Have a constructor that is autocalled for its usage statically.
3. Similar to number 2: have a method with environment as parameter (so you can test it), and the current one calls the new one with the imported environment as parameter.