[prefer-spy-on] skip over private methods as linted code doesn't compile

[rnveach]

original test:

    const privateMethodSpy = component['privateMethod'] = jest.fn();

    component.publicMethod();

    expect(privateMethodSpy).toHaveBeenCalledTimes(1);

The original test runs without issue.

linted test:

    const privateMethodSpy = jest.spyOn(component, 'privateMethod').mockImplementation();

    component.publicMethod();

    expect(privateMethodSpy).toHaveBeenCalledTimes(1);

The linted code fails to compile with "No overload matches this call".

No overload matches this call.
  Overload 1 of 3, '(object: Component, method: never): SpyInstance<never, never, any>', gave the following error.
    Argument of type 'string' is not assignable to parameter of type 'never'.
  Overload 2 of 3, '(object: Component, method: "ngOnInit" | "ngOnChanges" | "ngOnDestroy"): SpyInstance<void, [], any>', gave the following error.
    Argument of type '"privateMethod"' is not assignable to parameter of type '"ngOnInit" | "ngOnChanges" | "ngOnDestroy"'.
ts(2769)

[G-Rath]

I assume you're meaning TypeScripts version of private, in which case what the rule has done is valid as the code will still run correctly, and there's no way of knowing that the particular method is private just from the call site.

While it would be technically possible to determine this by making the rule type aware, I don't think we should as besides the additional work and maintenance of doing that, ultimately this is revealing a possibly unknown flaw in your suite: you're testing a private method (+ you're also overriding a method on a class).

You should be able to use // @ts-expect-error to suppress the type error, and that way you'll be explicitly marking it as known