Wednesday, January 25, 2017

FakeItEasy essentials

Today I had a closer look on FakeItEasy. A mockup (or faking) framework to create objects which can be configured freely from outside to be able to unit test classes working with these objects. Additionally it can create dummies (unneeded objects created to satisfy an interface).

FakeItEasy can be installed using nuget without any dependencies. Internally it uses the castle project (which makes me believe that FakeItEasy is more or less a super-powerfull dynamic proxy).

  • A.Fake<class or interface>(); (also CollectionOfFake)
    • tons of creation options can be added in overloaded Fake functions
      • e.g: WithArgumentsForConstructor, Implements,...
    • most interesting (for me) is .CallsBaseMethods so any object can be wrapped and be used with fakeiteasy magic
  • A.CallTo(...); // Properties: A.CallToSet
    • Arguments:
      • exact: "1", "xyz",..
      • by type: A<string>._
    • Conditions: WithReturnType, Where, To
    • ReturnValues: Throws, Returns, ReturnsNextFromSequence, ReturnsLayzily, ThrowsAsync, AssignOutAndRefParameters, AssignOutAndRefParametersLazily
    • Behaviors: DoesNothing, CallsBaseMethod, Invoke
    • Matchers: MustHaveHappened (Repeated), That.Matches(...)
  • Raise.Wtih


  • can not be used with static or sealed classes 
  • methods that are not virtual or abstract can not be overriden

It took me about 3 hours to read the docs and to test my sample, but I haven't found any show stoppers... Going to use it in my tests and look forward to write more about it...

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