Stale Mocks

A Stale Mock is an object that was faked in a previous test and currently been used in another test.
As a Stale Mock has no set behavior it could cause an unwanted behavior in your current test.

For Example:

C#

public class ClassUnderTest
{
    public static Dependency fooField ;

    public static int Foo()
    {
        return fooField.Bar();
    }
}
public class Dependency
{
    private int bar = 10;
    public int  Bar()
    {
        return bar;
    }
}

[TestClass, Isolated]
public class UnitTest1
{
    [TestMethod]
    public void CallingFakeInterfaceMethod_WillRerturn2()
    {
        //Arrange
        //setting the static field "fooField" as a fake of Dependency class
        var fakeDependency = Isolate.Fake.Instance<Dependency>();
        ClassUnderTest.fooField = fakeDependency;

        Isolate.WhenCalled(() => ClassUnderTest.fooField.Bar()).WillReturn(2);

        //Act
        var res = ClassUnderTest.Foo();

        //Assert
        Assert.AreEqual(2, res);
    }

    [TestMethod]
    public void CallingOriginalBarMethodWillReturn10()
    {
        //Act
        //When this test will run after the previous one the "fooField" will still be faked (a Stale Mock)
        //ClassUnderTest.Foo will return 0 as the "bar" field of Dependency hasn't been set to 10 becuase it was faked
        var res = ClassUnderTest.Foo();
        
        //Assert
        Assert.AreEqual(10,res);
    }
}

VB


Public Class ClassUnderTest
	Public Shared fooField As Dependency

	Public Shared Function Foo() As Integer
		Return fooField.Bar()
	End Function
End Class
Public Class Dependency
	Private bar As Integer = 10
	Public Function Bar() As Integer
		Return bar
	End Function
End Class

<TestClass,Isolated>
Public Class UnitTest1
	<TestMethod> 
	Public Sub CallingFakeInterfaceMethod_WillRerturn2()
		'Arrange
		'setting the static field "fooField" as a fake of Dependency class
		Dim fakeDependency = Isolate.Fake.Instance(Of Dependency)()
		ClassUnderTest.fooField = fakeDependency

		Isolate.WhenCalled(Function() ClassUnderTest.fooField.Bar()).WillReturn(2)

		'Act
		Dim res = ClassUnderTest.Foo()

		'Assert
		Assert.AreEqual(2, res)
	End Sub

	<TestMethod>
	Public Sub CallingOriginalBarMethodWillReturn10()
		'Act
		'When this test will run after the previous one the "fooField" will still be faked (a Stale Mock)
		'ClassUnderTest.Foo will return 0 as the "bar" field of Dependency hasn't been set to 10 becuase it was faked
		Dim res = ClassUnderTest.Foo()

		'Assert
		Assert.AreEqual(10, res)
	End Sub
End Class

Typemock will write Stale mock warnings to the output console.

A message will also appear on the Insight window:

To ignore the warning message use the following syntax:

Syntax

C#
[Isolated(IgnoreStaleMocks = true)]

VB
<Isolated(IgnoreStaleMocks:= true)>

This attribute can only be used on Class Level Attribute.