Cannot set property x of [object Module] which has only a getter

Error

debug.js:21 TypeError: Cannot set property AnalyticsService of [object Module] which has only a getter
    at <Jasmine>
    at new MockManager (mock-manager.js:26)
    at Function.push../node_modules/ts-mock-imports/lib/import-mock.js.ImportMock.mockClass (import-mock.js:15)
    at UserContext.<anonymous> (fbdb-requests.service.spec.ts:54)
    at ZoneDelegate.invoke (zone-evergreen.js:359)
    at ProxyZoneSpec.push../node_modules/zone.js/dist/zone-testing.js.ProxyZoneSpec.onInvoke (zone-testing.js:308)
    at ZoneDelegate.invoke (zone-evergreen.js:358)
    at Zone.run (zone-evergreen.js:124)
    at runInTestZone (zone-testing.js:561)
    at UserContext.<anonymous> (zone-testing.js:576)
    at <Jasmine>

Minimal code

import { ImportMock } from 'ts-mock-imports';
import * as analyticsModule from 'services/AnalyticsService';
analyticsServiceMock = ImportMock.mockClass(analyticsModule, 'AnalyticsService');

It’s that mock call that mockClass call that blows up. Similarly blows up with mockOther.

Cut down module attempted to be mocked

import * as utils from "utils";

//in the future this should subscribe to the various state services, plan, project, user, etc
// for now? leach off the old analytics service
export class AnalyticsService{
	private globals = {}
	multiselect(){ ... }
}

export let analyticsService = new AnalyticsService();
window.analyticsService = analyticsService;

Other things of note

• build: angular-cli v8
• testing framework: jasmine 3.4

Near as I’ve been able to tell, you’re unable to mock es6 imports because they’re supposed to be readonly. Which is roughly what the above illustrates. But I figured this package figured out some way around that limitation.

[altoblond]

The solution that worked for me is this one:

I had a module exporting a static function:

export class TimeProvider {
    /**
     * return the current date in the system
     */
    public static now(): Date {
        return new Date();
    }
}

and I use to mock it like this:

import * as TimeProviderModule from '@project/fwk-lib-core';
....
let timeProviderMock;
...
beforeEach(() => {
  timeProviderMock = ImportMock.mockStaticClass(TimeProviderModule, 'TimeProvider');
}
it('test', async () => {
        const nowMock: sinon.SinonStub = timeProviderMock.mock('now', date);
...
        expect(nowMock.calledOnce).toBe(true);
})

and I changed it to this:

import * as TimeProviderModule from '@project/fwk-lib-core';
....
let mockStaticF ;
...
beforeEach(() => {
        jest.mock('@project/fwk-lib-core/dist/time/time.provider');
        mockStaticF = jest.fn().mockReturnValue(date);
        TimeProvider.now = mockStaticF;
}
it('test', async () => {
...
        expect(mockStaticF).toBeCalledTimes(1);
})

effectively not using ts-mock-imports for static functions exported in external modules…

[jtheory]

Hi, it seems like this issue and the limitations that come with TS 3.9 should be at the top of the readme, in large text – otherwise this risks wasting a lot of developer time. 🙏

Typescript 3.9 introduced new functionality that blocks the key functionality of this library. With certain compilation structures, it is no longer possible to replace module exports. There is no true workaround for this issue.