Fake class Null safety

A stand-in for another object which cannot be used except for specifically overridden methods.

A fake has a default behavior for every field and method of throwing UnimplementedError. Fields and methods that are exercised by the code under test should be manually overridden in the implementing class.

A fake does not have any support for verification or defining behavior from the test, it cannot be used as a mock.

In most cases a shared full fake implementation without a noSuchMethod is preferable to extends Fake, however extends Fake is preferred against extends Mock mixed with manual @override implementations.

Example use:

// Real class.
class Cat {
  String meow(String suffix) => 'Meow$suffix';
  String hiss(String suffix) => 'Hiss$suffix';
}

// Fake class.
class FakeCat extends Fake implements Cat {
  @override
  String meow(String suffix) => 'FakeMeow$suffix';
}

void main() {
  // Create a new fake Cat at runtime.
  var cat = new FakeCat();

  // Try making a Cat sound...
  print(cat.meow('foo')); // Prints 'FakeMeowfoo'
  print(cat.hiss('foo')); // Throws
}

WARNING: Fake uses noSuchMethod, which is a form of runtime reflection, and causes sub-standard code to be generated. As such, Fake should strictly not be used in any production code, especially if used within the context of Dart for Web (dart2js, DDC) and Dart for Mobile (Flutter).