mock with a private field failed

[luckymark]

when I do this:

class Foo { 
    private field: string
}
let mock: Foo = Substitute.for<Foo>()

I get ：error TS2322: Type 'ObjectSubstitute<Pick<Foo, never>, Foo>' is not assignable to type 'Foo'.
Property 'field' is missing in type 'ObjectSubstitute<Pick<Foo, never>, Foo>'.

when I change "private" to "public", its ok!

[ffMathy]

What is the use case for this?

Why do you have a class only with private fields that you want to mock?

You should only test publically exposed functionality.

[joshribakoff]

Why do you have a class only with private fields that you want to mock?

He doesn't. He distilled the example, to simplify it for us.

You should only test publically exposed functionality.

Thats what hes trying to do...

class Foo { 
	private field: string
	public bar() {}
}
let mock: Foo = Substitute.for<Foo>() // error TS2322: 

The problem is he typed the mock to Foo, use the provided generic or let TS infer & it works fine:

ObjectSubstitute<OmitProxyMethods<Example>, Example>;

User error.

[luckymark]

@joshribakoff yes，I just simplify the test case！
In my use case, maybe I have a class :

class A{
   public needMock:Foo
}

the field needMock will be injected by some other code...I cant wait TS infer it!

[ffMathy]

Ah I see! Yes, that should be resolved as soon as possible!

I'll look into it sometime next week, as I am quite busy lately.

In the meanwhile, PRs are welcome!

[ffMathy]

I made a branch now called progress where I am refactoring the whole thing into being based on a strategy pattern.

You can follow up on the progress there. However, I don't have much time lately. Feel free to fork that branch and continue.

[ffMathy]

We can't fix this without breaking other things, until this feature is implemented:

microsoft/TypeScript#22677

[ilancohen]

@ffMathy - I really like this library, but without this fixed, using this library for Angular with its dependency injection is basically a non-starter. For instance, I have a class that depends on a service that I want to mock:

@Injectable({
  providedIn: "root"
})
export class LocaleService {
  constructor(private translate: TranslateService) {
  }

  getLocale() {
    return {};
  }

  getSupportedLocales(): any[] {
    return {};
  }
}

Mocking LocaleService (for usage in initializing your class) will throw a TS error, since translate is not defined.

Any suggestions? I'm happy to help fix this with a pull request, if you have a suggestion.

[ffMathy]

Can you provide a minimal example to reproduce it? Perhaps a PR that adds a unit test or similar? Or a separate project that demonstrates the problem?

[ilancohen]

I haven't tested it, but I think the code below provides a minimal example.
In this scenario, we're trying to mock ClassB to test ClassC:

class ClassA {
	constructor(){}

	methodA(): string {
		return 'abc'
	}
}

class ClassB {
	constructor(
		private classA: ClassA
	) {}

	methodB(): string {
		return this.classA.methodA();
	}

	methodB2(): string {
		return 'def'
	}
}

class ClassC {
	constructor(
		private classB: ClassB
	) {}

	methodC(): string {
		return this.classB.methodB2();
	}
}

const classBMock = Substitute.for<ClassB>();
const classC = new ClassC(classBMock);

Typescript will complain about that last line because classBMock lacks a member called classA.

[ffMathy]

Will investigate soon!

[ilancohen]

@ffMathy - I created a basic example, using your code.

[ffMathy]

Fixed. Thanks for making the library better!