Static Mocking

Static mocking is one of the advanced features supported in Telerik® JustMock. It allows you to fake static constructors, methods and properties calls, set expectations and verify results using the AAA principle.

We can divide static mocking into the following major parts:

  • Static constructor mocking
  • Static method mocking
  • Extension methods mocking

This is an Elevated Feature. Refer to this topic to learn more about the differences between both the commercial and free versions of Telerik JustMock.

Further in this topic we will use the following sample code to illustrate how to mock static constructors, methods and properties.

public class Foo 
{ 
    static Foo() 
    { 
        throw new NotImplementedException(); 
    } 
 
    public static void Submit() 
    { 
    } 
 
    public static int Execute(int arg) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public static int FooProp 
    { 
        get 
        { 
            throw new NotImplementedException(); 
        } 
        set 
        { 
            throw new NotImplementedException(); 
        } 
    } 
} 
 
internal class FooInternal 
{ 
    internal static void DoIt() 
    { 
        throw new NotImplementedException(); 
    } 
} 
 
public static class FooStatic 
{ 
    public static void Do() 
    { 
        throw new NotImplementedException(); 
    } 
} 
Public Class Foo 
    Shared Sub New() 
        Throw New NotImplementedException() 
    End Sub 
 
    Public Shared Sub Submit() 
        Throw New NotImplementedException() 
    End Sub 
 
    Public Shared Function Execute(arg As Integer) As Integer 
        Throw New NotImplementedException() 
    End Function 
 
    Public Shared Property FooProp As Integer 
        Get 
            Throw New NotImplementedException() 
        End Get 
        Set(value As Integer) 
            Throw New NotImplementedException() 
        End Set 
    End Property 
End Class 
 
Friend Class FooInternal 
    Friend Shared Sub DoIt() 
        Throw New NotImplementedException() 
    End Sub 
End Class 
 
Public NotInheritable Class FooStatic 
    Private Sub New() 
    End Sub 
    Public Shared Sub Do 
        Throw New NotImplementedException() 
    End Sub 
End Class 

Important

To use static mocking you first need to go to elevated mode by enabling JustMock from the menu. How to Enable/Disable

Static Constructor Mocking

In the following example you will see how you can specify the behavior of the static constructor when the target type is mocked. The first thing you need to do is to set up the target type for mocking all static calls. You do this using one of the following calls to the Mock.SetupStatic method.

void Mock.SetupStatic( Type staticType ); 
void Mock.SetupStatic( Type targetType, Behavior behavior ); 
void Mock.SetupStatic( Type staticType, StaticConstructor staticConstructor ); 
void Mock.SetupStatic( Type targetType, Behavior behavior, StaticConstructor staticConstructor ); 

As you can see you have a number of choices. You always have to provide the type of the target class you want to set up for mocking. You can also specify the behavior of the mock. The default behavior is Behavior.Loose.

The StaticConstructor parameter defines the default behavior of the static constructor. You can choose from the following values:

  • NonMocked
  • Mocked

The default value for this property is NonMocked.

Let's see a complete example using the class Foo from the sample code in the beginning.

[TestMethod] 
public void ShouldArrangeStaticFunction() 
{ 
    // Arrange 
    Mock.SetupStatic(typeof(Foo), StaticConstructor.Mocked); 
    int expected = 0; 
 
    Mock.Arrange(() => Foo.FooProp).Returns(0); 
 
    // Assert 
    Assert.AreEqual(expected, Foo.FooProp);   
} 
<TestMethod()> 
Public Sub ShouldArrangeStaticFunction() 
    ' Arrange 
    Mock.SetupStatic(GetType(Foo), StaticConstructor.Mocked) 
    Dim expected As Integer = 0 
 
    Mock.Arrange(Function() Foo.FooProp).Returns(0) 
 
    ' Assert             
    Assert.AreEqual(expected, Foo.FooProp) 
End Sub 

Here we have set up the static constructor mock of the target type Foo. Using the StaticConstructor parameter in the call to SetupStatic we have specified that we want to mock the call to the static constructor and therefore the call to the Foo.FooProp will not throw a NotImplementedException.

General Static Method Mocking

Let's start with the simplest example, namely how to mock the static Submit method. First, we need to call the following:

Mock.SetupStatic(typeof(Foo), StaticConstructor.Mocked); 
Mock.SetupStatic(GetType(Foo), StaticConstructor.Mocked) 

This call setups the Foo type for static mocking and prepares all the static methods as mockable.

This is actually the only difference between static and instance mocking. From now on you continue as if you are mocking instance methods.

Foo.Submit(); 
Foo.Submit() 

In the Submit method implementation we throw an exception, but as we mocked the Foo class that exception should not be thrown. Finally, we can assert that the method was actually called.

Mock.Assert(() => Foo.Submit()); 
Mock.Assert(Sub() Foo.Submit()) 

With Mock.SetupStatic(typeof(Foo), StaticConstructor.Mocked); we setup that all static methods from this class will me mocked. In certain cases you'd need to mock only methods that are setup with Mock.Arrange. To achieve this you need to set the M:Telerik.JustMock.Behavior to Strict in the Mock.SetupStatic call.

[TestMethod] 
[ExpectedException(typeof(StrictMockException))] 
public void ShouldThrowWhenNotArranged() 
{ 
    //Arrange 
    Mock.SetupStatic(typeof(Foo), Behavior.Strict, StaticConstructor.Mocked); 
 
    Mock.Arrange(() => Foo.Execute(10)).Returns(10); 
 
    //Assert 
    Assert.AreEqual(10, Foo.Execute(10)); 
 
    // Act 
    // throws MockException as there is no arrange associated with the Submit method 
    Foo.Submit(); 
} 
<TestMethod()> 
<ExpectedException(GetType(StrictMockException))> 
Public Sub ShouldThrowWhenNotArranged() 
    ' Arrange 
    Mock.SetupStatic(GetType(Foo), Behavior.Strict, StaticConstructor.Mocked) 
 
    Mock.Arrange(Function() Foo.Execute(10)).Returns(10) 
 
    ' Assert 
    Assert.AreEqual(10, Foo.Execute(10)) 
 
    ' Act 
    ' Throws MockException as there is no arrange associated with the Submit method. 
    Foo.Submit() 
End Sub 

Once we set the M:Telerik.JustMock.Behavior to Strict, only calls setup through arrange are mocked. Other calls will throw a MockException.

Follows an example of mocking static method in F#:

[<Test()>] 
    member this.ShouldMockStaticCall() =   
 
    Mock.SetupStatic<Foo>() 
 
    Mock.Arrange(fun ignore -> Foo.EchoStatic()).Returns(1); 
 
    Assert.AreEqual(1, Foo.EchoStatic()) 
The static EchoStatic method is arranged to return 1.

Mocking Static Property Get

You can also set up a static property get:

[TestMethod] 
public void ShouldFakeStaticPropertyGet() 
{ 
    // Arrange 
    Mock.SetupStatic(typeof(Foo), Behavior.Strict, StaticConstructor.Mocked); 
 
    bool called = false; 
 
    Mock.Arrange(() => Foo.FooProp).DoInstead(() => { called = true; }).Returns(1); 
 
    // Assert 
    Assert.AreEqual(Foo.FooProp, 1); 
    Assert.IsTrue(called); 
} 
<TestMethod()> 
Public Sub ShouldFakeStaticPropertyGet() 
    ' Arrange 
    Mock.SetupStatic(GetType(Foo), Behavior.Strict, StaticConstructor.Mocked) 
 
    Dim called As Boolean = False 
 
    Mock.Arrange(Function() Foo.FooProp).DoInstead(Sub() called = True).Returns(1) 
 
    ' Act 
    Assert.AreEqual(Foo.FooProp, 1) 
    Assert.IsTrue(called) 
End Sub 

We replace the actual implementation of Foo.FooProp with called = true; and return 1. After acting we verify that the method was actually called with return value 1.

Mocking Static Property Set

Now, let's mock a static property set. In the example below, we arrange the Foo.FooProp property. We use DoInstead to set a local boolean variable to true once it is assigned 10. After that, we verify that what we have expected actually happened in our test.

[TestMethod] 
public void ShouldFakeStaticPropertySet() 
{ 
    // Arrange 
    Mock.SetupStatic(typeof(Foo), Behavior.Strict, StaticConstructor.Mocked); 
 
    bool called = false; 
 
    Mock.ArrangeSet(() => { Foo.FooProp = 10; }).DoInstead(() => { called = true; }); 
 
    // Act - this line should not throw any mockexception. 
    Foo.FooProp = 10; 
 
    // Assert 
    Assert.IsTrue(called); 
} 
<TestMethod()> 
Public Sub ShouldFakeStaticPropertySet() 
    ' Arrange 
    Mock.SetupStatic(GetType(Foo), Behavior.Strict, StaticConstructor.Mocked) 
 
    Dim called As Boolean = False 
 
    Mock.ArrangeSet(Sub() Foo.FooProp = 10).DoInstead(Sub() called = True) 
 
    ' Act - this line should not throw any mockexception. 
    Foo.FooProp = 10 
 
    ' Assert 
    Assert.IsTrue(called) 
End Sub 

Go to Mock Properties topic to learn more about mocking properties.

Mocking Internal Static Call

Going further, you can mock internal methods like in the following example.

[TestMethod] 
public void ShouldFakeInternalStaticCall() 
{ 
    // Arrange 
    Mock.SetupStatic<FooInternal>(); 
 
    // Act 
    FooInternal.DoIt(); 
} 
<TestMethod()> 
Public Sub ShouldFakeInternalStaticCall() 
    ' Arrange 
    Mock.SetupStatic(Of FooInternal)() 
 
    ' Act 
    FooInternal.DoIt() 
End Sub 

Here, calling FooInternal.DoIt should not throw an exception as you are allowed to setup static internal methods.

Mocking Static Class

In the demonstrated examples, the class itself that we mock is a non static class - only the methods are static. To mock a static class you need to use the non generic version of the Mock.SetupStatic method, i.e.

[TestMethod] 
public void ShouldMockStaticClass() 
{ 
    // Arrange 
    Mock.SetupStatic(typeof(FooStatic)); 
 
    // Act - doesn't throw MockException 
    FooStatic.Do(); 
} 
<TestMethod()> 
Public Sub ShouldMockStaticClass() 
    ' Arrange 
    Mock.SetupStatic(GetType(FooStatic)) 
 
    ' Act - doesn't throw MockException 
    FooStatic.Do 
End Sub 

Mocking Static Members Across Threads

Mocking static members across all threads is an unsafe operation that may compromise the stability of the testing framework. Arrangements on static members are valid only for the current thread by default. To make an arrangement on a static member valid on all threads, add the .OnAllThreads() clause to the arrangement:

Mock.Arrange(() => DateTime.Now).Returns(new DateTime()).OnAllThreads(); 

Mocking Current HttpContext

Here is an example how to mock the current HTTP context.

We arrange a call to HttpContext.Current to set a local variable to true. Note that the original implementation of HttpContext.Current won`t be executed.

[TestMethod] 
public void ShouldAssertMockingHttpContext() 
{ 
    // Arrange 
    bool called = false; 
    Mock.Arrange(() => HttpContext.Current).DoInstead(() => called = true); 
 
    // Act 
    var ret = HttpContext.Current; 
 
    // Assert 
    Assert.IsTrue(called); 
} 
<TestMethod> _ 
Public Sub ShouldAssertMockingHttpContext() 
    ' Arrange 
    Dim called As Boolean = False 
    Mock.Arrange(Function() HttpContext.Current).DoInstead(Sub() called = True) 
 
    ' Act 
    Dim ret = HttpContext.Current 
 
    ' Assert 
    Assert.IsTrue(called) 
End Sub 

After acting we verify against our expectations.

Mocking Extension Methods

An extension method is a new language feature of C# starting with the 3.0 specifications, as well as Visual Basic.NET starting with 9.0. Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static methods, but they are called as if they were instance methods on the extended type.

Mocking extension method is similar to mocking any instance methods. The only difference is that we don’t need Mock.Create<T>() call to initialize the class for mocking as extension mocking is by default partial.

Let's see an example of how to mock extension methods. Consider the following class:

public class Bar 
{ 
    public void Execute() 
    { 
        throw new NotImplementedException(); 
    } 
} 
Public Class Bar 
    Public Sub Execute() 
        Throw New NotImplementedException() 
    End Sub 
End Class 

And a class that contains extension methods for the Foo class:

public static class BarExtensions 
{ 
    public static int Echo(this Bar foo, int arg) 
    { 
        return default(int); 
    } 
} 
Public Module BarExtensions 
    <System.Runtime.CompilerServices.Extension()> 
    Public Function Echo(foo As Bar, arg As Integer) As Integer 
        Return 0 
    End Function 
End Module 

Let's mock the Echo extension method.

[TestMethod] 
public void ShouldFakeExtensionMethod() 
{ 
    // Arrange 
    var foo = new Bar(); 
 
    Mock.Arrange(() => foo.Echo(10)).Returns(11); 
 
    // Act 
    var actual = foo.Echo(10); 
 
    // Assert 
    Assert.AreEqual(11, actual); 
} 
<TestMethod()> 
Public Sub ShouldFakeExtensionMethod() 
    ' Arrange 
    Dim foo = New Bar() 
 
    Mock.Arrange(Function() foo.Echo(10)).Returns(11) 
 
    ' Act 
    Dim actual = foo.Echo(10) 
 
    ' Assert 
    Assert.AreEqual(11, actual) 
End Sub 

First we create an instance of the Foo class. Notice that we create a standard instance of the class, not a mock instance. Then we setup the call to Echo through Arrange in the same way we do it for non static methods. Finally, we assert the return value as usual.

See Also

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