Modifying the Method Behavior

You can specify how you want a method to behave when you call it. For example, you can define that when the method is called, its original implementation should be invoked. Alternatively, you can force throwing an exception or returning a test collection of data.

When to Use

You can modify the behavior of a specific fake method when your test requires a specific return value from the method.

To ensure that minor changes to production code will not break your test, by default, Typemock Isolator ignores all arguments passed to fake methods. See here how to fake methods based on call arguments.

Syntax

C#

Isolate.WhenCalled(() => fake.Increment()).<behavior>;

VB

Isolate.WhenCalled(Function() fake.Increment()).<behavior>

The following table explains possible behaviors:

Behavior	Description
CallOriginal()	When the method is called, call the original implementation.
ReturnRecursiveFakes()	Returns: • For reference types: fake objects • For other return types: zero or equivalent The returned fake objects will behave in the same way.
WillThrow()	Throws a specified exception.
WillReturn()	Return a specified value. This is applicable only to those methods that return values.
IgnoreCall()	Returns immediately. This is applicable only to void methods.
WillReturnCollectionValuesOf()	Returns a collection of test data.
DoInstead()	Calls a user code. This option is used for advanced and complex behaviors.

Samples

Sample 1: Ignoring Call

C#

Isolate.WhenCalled(() => fake.Increment()).IgnoreCall();

VB

Isolate.WhenCalled(Sub() fake.Increment()).WillBeIgnored()

Sample 2: Setting Different Behavior on Overloaded Methods

To set a different behavior to overloaded methods, use WhenCalled() on each overload.

The last overload method behavior setting is the default behavior for all overloads.

C#

// Note: Use Isolated to clean up after the test
[TestMethod, Isolated] 
public void Overloaded_Example()
{
  var fakeDependency = Isolate.Fake.Instance<Dependency>();
  // Each overloaded method will act as a separate sequence
  Isolate.WhenCalled(() => fakeDependency.OverloadedMethod(1)).WillReturn(2);
  Isolate.WhenCalled(() => fakeDependency.OverloadedMethod("Typemock Rocks")).WillReturn(9);

  var result = new ClassUnderTest().AddOverloadedDependency(fakeDependency);

  Assert.AreEqual(11, result);
}

public int AddOverloadedDependency(Dependency dependency)
{
  return dependency.OverloadedMethod(12) + dependency.OverloadedMethod("typemock");
}

VB

' Note: Use Isolated to clean up after the test
<TestMethod(), Isolated()> _
Public Sub Overloaded_Example()
    Dim fakeDependency = Isolate.Fake.Instance(Of Dependency)()
    ' Each overloaded method will act as a separate sequence
    Isolate.WhenCalled(Function() fakeDependency.OverloadedMethod(1)).WillReturn(2)
    Isolate.WhenCalled(Function() fakeDependency.OverloadedMethod("Typemock Rocks")).WillReturn(9)

    Dim result = New ClassUnderTest().AddOverloadedDependency(fakeDependency)

    Assert.AreEqual(11, result)
End Sub

Public Function AddOverloadedDependency(dependency As Dependency) As Integer
  Return dependency.OverloadedMethod(12) + dependency.OverloadedMethod("typemock")
End Function

Isolator also have an option to change the method logic using the DoInstead feature.