Mocking Ref Returns

Ref return is one of the advanced features supported in Telerik® JustMock. It gives you ability to arrange and verify expectations of public and non-public instance and static ref return methods and properties in elevated mode.

Ref return is a feature specific for C# language and have limited support in other CLR languages. To use ref return mocking, you have to enable profiler for elevated mode. You can refer to this topic for more information about advanced features and how to enable them.

ClassUsingRefReturns sample class is used below to figure out different ref return use cases. Here is its implementation:

• C#

class ClassUsingRefReturns 
{ 
    private static int[] array = { 1, 2, 3, 4 }; 
 
    public ref int GetRefReturnInstanceWithArgs(ref int p) 
    { 
        ref int local = ref array[0]; 
        local += p; 
 
        return ref local; 
    } 
 
    private ref int GetRefReturnPrivInstanceWithArgs(ref int p) 
    { 
        ref int local = ref array[1]; 
        local += p; 
 
        return ref local; 
    } 
 
    public static ref int RefReturnStatic 
    { 
        get 
        { 
            return ref array[2]; 
        } 
 
    } 
 
    private static ref int RefReturnPrivStatic 
    { 
        get 
        { 
            return ref array[3]; 
        } 
    } 
} 

Mocking Public Ref Return Members

The typical example of mocking public instance method could be illustrated as following:

• C#

[TestMethod] 
public void MockRefReturnInstanceMethodWithArgs() 
{ 
    var localRef = LocalRef.WithValue(12); 
 
    // Arrange 
    var sut = Mock.Create<ClassUsingRefReturns>(); 
    Mock.Arrange(sut, s => s.GetRefReturnInstanceWithArgs(ref Arg.Ref(Arg.AnyInt).Value))) 
        .Returns(localRef.Handle) 
        .OccursOnce(); 
 
    // Act 
    int param = 10; 
    ref int res = ref sut.GetRefReturnInstance(ref param); 
 
    // Assert 
    Mock.Assert(sut); 
    Assert.AreEqual(localRef.Ref, res); 
} 

In this example, there is an arrangement to fake ref return and verify occurrences of instance method using Mock.Arrange. The interesting part of this arrangement is to provide a value which can be considered as ref return. JustMock introduces a dedicated delegate type FuncExpectation<TReturn>.RefDelegate for this purpose and LocalRef helper class which simplifies ref return arrangements and verifications.

Important

Ref return fakes are implemented via delegates. LocalRef helper class hides a lot of implementation details and makes your test code easy to maintain.

Another common use case is mocking of public static member. The next example shows how to achieve that:

• C#

[TestMethod] 
public void MockRefReturnStaticProperty() 
{ 
    // Arrange 
    Mock.SetupStatic<ClassUsingRefReturns>(); 
    Mock.Arrange<ClassUsingRefReturns, int>(() =>ClassUsingRefReturns.RefReturnStatic) 
        .Returns(LocalRef.WithValue(12).Handle) 
        .OccursOnce(); 
 
    // Act 
    ref int res = ref ClassUsingRefLocalsAndReturns.RefReturnStatic; 
 
    // Assert 
    Mock.Assert<ClassUsingRefReturns>(); 
    Assert.AreEqual(12, res); 
} 

Mocking Non-public Ref Return Members

Non-public API provides several dedicated interfaces for mocking ref returns and accessing members following a well-known JustMock approach. Let's see how this looks like in action:

• C#

[TestMethod] 
public void MockRefReturnPrivateInstanceMethodWithArgs() 
{ 
    // Arrange 
    var sut = Mock.Create<ClassUsingRefReturns>(); 
    Mock.NonPublic.RefReturn.Arrange<int>(sut, "GetRefReturnPrivInstanceWithArgs", Arg.Expr.Ref(1)) 
        .Returns(LocalRef.WithValue(12).Handle) 
        .OccursOnce(); 
 
    // Act 
    var accessor = Mock.NonPublic.MakePrivateAccessor(sut); 
    ref int res = ref accessor.RefReturn.CallMethod<int>("GetRefReturnPrivInstanceWithArgs", Arg.Ref(1).Value); 
 
    // Assert 
    Mock.Assert(sut); 
    Assert.AreEqual(12, res); 
} 

The example demonstrates ref return faking and occurrence verification handled by INonPublicRefReturnExpectation interface. Accessing non-public members is supported via IPrivateRefReturnAccessor interface as a part of PrivateAccessor. The next example gives an idea of how you can mock non-public ref return static members:

• C#

[TestMethod] 
public void MockRefReturnPrivateStaticProperty() 
{ 
    // Arrange 
    Mock.SetupStatic<ClassUsingRefReturns>(); 
    Mock.NonPublic.RefReturn.Arrange<ClassUsingRefReturns, int>("RefReturnPrivStatic") 
        .Returns(LocalRef.WithValue(12).Handle) 
        .OccursOnce(); 
 
    // Act 
    var accessor = Mock.NonPublic.MakeStaticPrivateAccessor(typeof(ClassUsingRefReturns)); 
    ref int res = ref accessor.RefReturn.GetProperty<int>("RefReturnPrivStatic"); 
 
    // Assert 
    Mock.Assert<ClassUsingRefReturns>(); 
    Assert.AreEqual(12, res); 
}