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isMockValidator is useful when we need to access the callback which was set via registerOnValidatorChange on a mock object which has implemented Validator or AsyncValidator, and to call __simulateValidatorChange to trigger it. It verifies whether an instance respects MockValidator interface.

We need it when we get an error like:

Property '__simulateValidatorChange' does not exist on type <class>

const instance = ngMocks.findInstance(MyValidatorDirective);// instance.simulateValidatorChange(); // does not work.if (isMockValidator(instance)) {  // now works  instance.__simulateValidatorChange();}