Create & Fake

Mocking and data generation for testing.

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The Faker tool provides fakes to imitate object behavior for testing:

  • Mock - Strict fake where calls throw exceptions if not set up.
  • Stub - Loose fake where calls return defaults if not set up.

For attributes:

  • [Fake] - Loose fake with all methods randomized by the Randomizer.
  • [Stub] - Same as regular Stub behavior.


Fakes use a typical lambda based style with a very methodical structure:

/// <summary>Verifies setup functionality.</summary>
public void Setup_ObjectEquality()
    object data = new object();

    Fake<object> fake = Tools.Faker.Mock<object>();
        d => d.Equals(Arg.Any<object>()),
        Behavior.Returns(false, Times.Once));
        d => d.Equals(data),
        Behavior.Returns(true, Times.Once));

    Tools.Asserter.Is(false, fake.Dummy.Equals(new object()));
    Tools.Asserter.Is(true, fake.Dummy.Equals(data));


The functionality is based upon only a few components:

  • Arg - Useful for matching parameters by various conditions.
  • Behavior - Used to define what happens when the mocked method is called.
  • Times - Specifies expected number of calls.

Creation & Customization

The Faker requires a Valuer to be given at creation, which controls value equality behavior for parameter matching.


There are a variety of options to verify methods were called as expected:

  • Fake.VerifyAll() - Automatically checks methods based upon Times in each Behavior.
  • Fake.VerifyAll(Times) - Does the above and that the total matches the provided Times.
  • Fake.Verify(Times, delegate) - Verifies the given delegate was called the given Times.
  • Fake.VerifyTotalCalls(Times) - Only verifies the total number of calls made.

Voids & Generics

There are two special useful types provided:

  • VoidType - Used to specify void for return type on behaviors.
  • AnyGeneric - Used to match any generic in setup methods.

Faking Internal

The assembly containing the internals to fake needs to grant visibility to the dynamic assembly by adding somewhere (typically AssemblyInfo.cs):

[assembly: InternalsVisibleTo("FakerTypes")]

Faking Protected

The fakes can be setup using the string names for protected methods with an array containing the parameters to match. However, note that using Arg conditions requires the .Lambda versions to successfully match calls.

/// <summary>Verifies hints generate the hashes.</summary>
public void GetHashCode_ValidHint()
    object data = new object();
    int result = Tools.Randomizer.Create<int>();

    Fake<CompareHint> hint = Tools.Faker.Mock<CompareHint>();
        new[] { data, data, Arg.LambdaAny<ValuerChainer>() },
        Behavior.Returns(true, Times.Once));
        new[] { data, Arg.LambdaAny<ValuerChainer>() },
        Behavior.Returns(result, Times.Once));

    Tools.Asserter.Is(result, new Valuer(false, hint.Dummy).GetHashCode(data));

Faking Ref & Out

The special class OutRef is used to handle reference behavior:

/// <summary>Verifies faking works with out and ref arguments.</summary>
[Theory, RandomData]
public void Fake_HandlesOut(string data, string start)
    Fake<OutRefSample> fake = Tools.Faker.Mock<OutRefSample>();
        d => d.WithOut(out Arg.AnyRef<string>().Var),
        Behavior.Set((OutRef<string> d) => { d.Var = data; }, Times.Once));
        d => d.WithRef(ref Arg.WhereRef<string>(v => v == start).Var),
        Behavior.Set((OutRef<string> d) => { d.Var = data; }, Times.Once));

    fake.Dummy.WithOut(out string outValue);
    Tools.Asserter.Is(data, outValue);

    string refValue = start;
    fake.Dummy.WithRef(ref refValue);
    Tools.Asserter.Is(data, refValue);