Explain how ngOnChange hook behaves during unit tests

[rooby]

Description

There seems to be a lot of people unaware of the unexpected behaviour of ngOnChange not being called when doing something like:

TestBed.configureTestingModule({}).compileComponents().then(() => {
    fixture = TestBed.createComponent();
    fixture.detectChanges();
});

It is not obvious that ngOnChange will not be called when doing this, therefore please provide a clarification in the testing docs.
It would be great to also provide some strategy/strategies for how to test a component which depends on the ngOnChange hook.

Issue taken from angular/angular.io#3277
Relating to #9866

What is the affected URL?

No response

Please provide the steps to reproduce the issue

No response

Please provide the expected behavior vs the actual behavior you encountered

No response

Please provide a screenshot if possible

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Please provide the exception or error you saw

No response

Is this a browser-specific issue? If so, please specify the device, browser, and version.

No response

[petebacondarwin]

I think the testing strategy is to call the ngOnChanges() directly.
We should update the docs to point out that if a component is created programmatically then it does not exist in a context that would trigger this life-cycle hook automatically, so must be done manually when setting properties on the component.

[jessicajaniuk]

Fixit Note: We should document that when you're setting inputs on a test component or dynamically created component, do it on the helper.

[coyoteecd]

@jessicajaniuk which helper?