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Mocking Non-public Members and Types

This article provides various examples that demonstrate how to mock non-public members and types with Telerik® JustMock.

Introduction

You can use JustMock to mock non-public members and types in elevated mode. That is useful when you want to isolate calls to non-public members and types, such as:

  • private calls, methods, and interfaces
  • private static methods and properties
  • protected members
  • internal classes
  • internal virtual methods and properties

This feature is available only in the commercial version of Telerik JustMock. Refer to this topic to learn more about the differences between the commercial and free versions.

If you need a complete Visual Studio project that demonstrates how to mock non-public members and types, refer to the examples in the installation directory. The default installation directory is C:\Program Files (x86)\Progress\Telerik JustMock\Examples.

Prerequisites

In the next examples, we will use the following sample class to test:

Sample setup

public class Foo 
{ 
    private void DoPrivate() 
    { 
        throw new NotImplementedException(); 
    } 
 
    private void DoPrivate(int arg) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public void DoPublic() 
    { 
        DoPrivate(); 
    } 
 
    private void DoPrivateGeneric<T>(T arg) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public void DoPublicGeneric<T>(T arg) 
    { 
        DoPrivateGeneric<T>(arg); 
    } 
 
    public void Execute(int arg) 
    { 
        DoPrivate(arg); 
    } 
 
    private int PrivateEcho(int arg) 
    { 
        return arg; 
    } 
 
    public int Echo(int arg) 
    { 
        return PrivateEcho(arg); 
    } 
 
    internal virtual void Do() 
    { 
        throw new NotImplementedException(); 
    } 
 
    internal virtual string Value 
    { 
        get 
        { 
            throw new NotImplementedException(); 
        } 
        set 
        { 
            throw new NotImplementedException(); 
        } 
    } 
 
    private static int PrivateStaticProperty { get; set; } 
 
    public int GetMyPrivateStaticProperty() 
    { 
        return PrivateStaticProperty; 
    } 
}

Important

To mock non-public members and types, you first need to go to elevated mode by enabling JustMock from the menu. Learn how to do that in the How to Enable/Disable Telerik JustMock topic.

Step by Step Description

The following list describes the steps you should perform in order to mock a non-public member:

  1. Create an instance of the type that you want to test.
  2. Use the Mock.NonPublic modifier to mock a non-public member.
  3. Add the arrange statement:
    1. Pass the target object to test.
    2. Pass the member name that you want to test as a string.
    3. If you test a method, pass the arguments.

Example 1 shows how to set up that a call to the DoPrivate method of the Foo class must set a local variable called. This way you override the original method behavior with the one that you specify.

Example 1: Change the behavior of a private method

[TestMethod] 
public void ShouldInvokeNonPublicMember() 
{ 
    Foo foo = new Foo(); 
 
    bool called = false; 
 
    // Arrange 
    Mock.NonPublic.Arrange(foo, "DoPrivate").DoInstead(() => called = true); 
 
    // Act 
    foo.DoPublic(); 
 
    // Assert 
    Assert.IsTrue(called); 
}

Mock.NonPublic can be also used to mock generic non-public methods. In addition to the non-generic method mock, the generic type arguments must be supplied in the arrangement.

Example 2: Change the behavior of a generic non-public method

[TestMethod] 
public void ShouldInvokeNonPublicGenericMember() 
{ 
    Foo foo = new Foo(); 
 
    bool called = false; 
 
    // Arrange 
    Mock.NonPublic.Arrange(foo, "DoPrivateGeneric", new Type[] { typeof(int) }, 10).DoInstead(() => called = true); 
 
    // Act 
    foo.DoPublicGeneric<int>(10); 
 
    // Assert 
    Assert.IsTrue(called); 
}

Private Members

Private Methods with Parameters

Example 3 shows how you can arrange a call to a private method accepting an argument that matches any integer value. The example arranges the PrivateEcho to return 1 when called with any int parameter. In the acting phase, the PrivateEcho method is called with 5 as argument.

For more details on how to work with parameters when mocking, check the Matchers help topic.

Example 3: Change the behavior of a non-public method with parameter

[TestMethod] 
public void ShouldInvokeNonPublicMemberWithMatcher() 
{ 
    Foo foo = new Foo(); 
 
    int expected = 1; 
 
    // Arrange 
    // PrivateEcho will always return 1 when invoked with an int parameter 
    Mock.NonPublic.Arrange<int>(foo, "PrivateEcho", Arg.Expr.IsAny<int>()).Returns(expected); 
 
    // Act 
    int actual = foo.Echo(5); 
 
    // Assert 
    Assert.AreEqual(expected, actual); 
}

Private Methods with Overloads

In this section, you will find how to arrange a call to a private method with two overloads. The following class will be used as an example:

Sample setup

internal class FooInternal 
{ 
    private void pExecute(int arg1) 
    { 
        throw new NotImplementedException(); 
    } 
 
    private void pExecute() 
    { 
        throw new NotImplementedException(); 
    } 
 
    public void Execute(int arg1) 
    { 
        pExecute(arg1); 
    } 
 
    public void Execute() 
    { 
        pExecute(); 
    } 
}

Important

To interact with non-public classes, you must add the InternalVisibleTo property inside the AssemblyInfo.cs in the project you need to test, like this: 

[assembly: InternalsVisibleTo("YourTestProject")]

In the sample setup shown above, the pExecute method has two overloads - one without arguments and one accepting an integer value as an argument. The code in Example 4 mocks the overload that accepts an integer. The behavior of the method is arranged to set a local boolean variable to true once it is called with 10 as argument. After that, it acts by calling foo.Execute(10) and verifies that called is true.

Example 4: Mock private method with overloads

[TestMethod] 
public void ShouldInvokeNonPublicMemberWithOverloads() 
{ 
    FooInternal foo = new FooInternal(); 
    bool isCalled = false; 
 
    // Arrange 
    Mock.NonPublic.Arrange(foo, "pExecute", 10).DoInstead(() => isCalled = true); 
 
    // Act 
    foo.Execute(10); 
 
    // Assert 
    Assert.IsTrue(isCalled); 
}

Private Implementation of an Interface Method

This section shows how you can mock an explicit (not public) interface implementation method from current or base class.

The following classes will be used:

Sample setup

public interface IManager 
{ 
    object Provider { get; } 
} 
 
public class FooBase : IManager 
{ 
    object IManager.Provider 
    { 
        get { throw new NotImplementedException(); } 
    } 
} 
 
public class Bar : FooBase 
{ 
    //... 
}

As you can see from the sample above, the IManager interface defines the Provider property, which is then implemented in FooBase. The concrete implementation we need to test, however, resides in the Bar class, which uses the FooBase.Provider property. In Example 5 you will see how you can mock the Provider property.

Example 5: Mock the implementation of a private method defined in an interface

[TestMethod] 
public void ShouldMockPrivateInterfaceImplementationMethod() 
{ 
    const string expected = "dummy"; 
 
    // Arrange 
    var bar = Mock.Create<Bar>(); 
    Mock.Arrange(() => ((IManager)bar).Provider).Returns(expected); 
 
    // Act, Assert 
    Assert.AreEqual(expected, ((IManager)bar).Provider); 
}

Internal Virtual Members

Internal Virtual Method

Mocking internal virtual methods uses similar approach to mocking public members. To demonstrate how you can use JustMock to mock an internal virtual method, we will be using the Do method from the sample setup in the beginning of this topic.

Example 6: Mock internal virtual method

[TestMethod] 
public void ShouldMockInternalVirtualMethod() 
{ 
    Foo foo = new Foo(); 
 
    bool isCalled = false; 
 
    // Arrange 
    Mock.Arrange(() => foo.Do()).DoInstead(() => isCalled = true); 
 
    // Act 
    foo.Do(); 
 
    // Assert 
    Assert.IsTrue(isCalled); 
}

Note that, in the arrange statement, it is not used a mock of Foo, but the actual instance.

Internal Virtual Property Get And Set

Arranging an internal virtual property is also similar to arranging a public property.

Example 7: Mock internal virtual property get

[TestMethod] 
public void ShouldMockInternalVirtualPropertyGET() 
{ 
    Foo foo = new Foo(); 
 
    // Arrange 
    Mock.Arrange(() => foo.Value).Returns("ping"); 
 
    // Act 
    string actual = foo.Value; 
 
    // Assert 
    Assert.AreEqual("ping", actual); 
}

Note that, in the arrange statement, it is not used a mock of Foo, but the actual instance.

The following code is an example of mocking internal virtual property set. The code overrides the actual implementation by arranging that the foo.Value must be called with a certain value.

Example 8: Mock internal virtual property set

[TestMethod] 
public void ShouldMockInternalVirtualPropertySET() 
{ 
    // Arrange 
    Foo foo = Mock.Create<Foo>(); 
    Mock.ArrangeSet(() => foo.Value = "ping").MustBeCalled(); 
 
    // Act 
    foo.Value = "ping"; 
 
    // Assert 
    Mock.Assert(foo); 
}

Private Static Members

Private Static Method

The following example shows how to mock a private static method. We use the following sample class:

Sample setup

internal class FooInternalStatic 
{ 
    private static int EchoPrivate(int arg1) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public static int Echo(int arg1) 
    { 
        return EchoPrivate(arg1); 
    } 
 
    private static int EchoPrivateGeneric<T>(T arg1) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public static int EchoGeneric<T>(T arg1) 
    { 
        return EchoPrivateGeneric<T>(arg1); 
    } 
}

Important

To interact with non-public classes, you should add the InternalVisibleTo property inside the AssemblyInfo.cs in the project you need to test, like this: 

[assembly: InternalsVisibleTo("YourTestProject")]

The method arranged in Example 9 is FooInternalStatic.EchoPrivate().

Example 9: Mock private static method

[TestMethod] 
public void ShouldMockPrivateStaticMethod() 
{ 
    // Arrange 
    Mock.NonPublic.Arrange<FooInternalStatic, int>("EchoPrivate", 10); 
 
    // Act 
    FooInternalStatic.Echo(10); 
 
    // Assert 
    Mock.NonPublic.Assert<FooInternalStatic, int>("EchoPrivate", 10); 
}

The code in Example 9 calls the Echo method, but its implementation calls the EchoPrivate method, so the assertion passes.

Like with non-public instance generic methods, Mock.NonPublic can be used to mock non-public static generic ones.

Example 10: Mock non-public static generic method

[TestMethod] 
public void ShouldMockPrivateStaticGenericMethod() 
{ 
    // Arrange 
    Mock.NonPublic.Arrange<FooInternalStatic, int>("EchoPrivateGeneric", new Type[] { typeof(int) }, 10); 
 
    // Act 
    FooInternalStatic.EchoGeneric<int>(10); 
 
    // Assert 
    Mock.NonPublic.Assert<FooInternalStatic, int>("EchoPrivateGeneric", new Type[] { typeof(int) }, 10); 
}

Private Static Property

This section shows how to mock the get function of a private static property. The Foo class defined above is used as a sample setup.

The property arranged in Example 11 is Foo.PrivateStaticProperty. When called, it will return an expected integer value, different from the default one.

Example 11: Mock private static property

[TestMethod] 
public void ShouldMockPrivateStaticProperty() 
{ 
    var expected = 10; 
 
    // Arrange 
    Foo foo = new Foo(); 
 
    Mock.NonPublic.Arrange<int>(typeof(Foo), "PrivateStaticProperty").Returns(expected); 
 
    // Act 
    int actual = foo.GetMyPrivateStaticProperty(); 
 
    // Assert 
    Assert.AreEqual(expected, actual); 
}

To act, the code calls the GetMyPrivateStaticProperty() method, but its implementation returns the PrivateStaticProperty, so the assertion passes.

Protected Members

To show how to mock a protected member, we will use the following class:

Sample setup

public class FooWithProtectedMembers 
{ 
    protected virtual void Load() 
    { 
        throw new NotImplementedException(); 
    } 
 
    protected virtual int IntValue 
    { 
        get 
        { 
            throw new NotImplementedException(); 
        } 
    } 
 
    public virtual void Init() 
    { 
        Load(); 
    } 
}

To mock protected members in JustMock, you can use the same method and logic, as for the rest non-public types, previously shown in this topic.

First, we will arrange that our IntValue() method must never occur::

Example 12: Arrange protected method

[TestMethod] 
public void ShouldAssertOccrenceForNonPublicFunction() 
{ 
    var foo = Mock.Create<FooWithProtectedMembers>(Behavior.CallOriginal); 
 
    Mock.NonPublic.Assert<int>(foo, "IntValue", Occurs.Never()); 
}

The second test will test if the protected Load() method is actually been called, when Init() is initiated.

Example 13: Arrange that a protected method must be called at least once

[TestMethod] 
public void ShouldMockProtectedVirtualMembers() 
{ 
    var foo = Mock.Create<FooWithProtectedMembers>(Behavior.CallOriginal); 
 
    Mock.NonPublic.Arrange(foo, "Load").MustBeCalled(); 
 
    foo.Init(); 
 
    Mock.Assert(foo); 
}

Important

To mock a protected type, your assembly name must be fully qualified according to the framework design rules, i.e. assembly name = namespace. Note that you can't mock types from mscorlib in this way.

Internal Class

Let's see an example of how to mock an internal class from .NET. Consider the System.Net.HttpRequestCreator class, which is internal, but has a public interface System.Net.IWebRequestCreate. Example 14 mocks its Create method.

Example 14: Mock internal class

[TestMethod] 
public void ShouldMockInternaldotNETClass() 
{ 
    // Arrange 
    string typeName = "System.Net.HttpRequestCreator"; 
 
    var httpRequestCreator = Mock.Create(typeName); 
 
    bool isCalled = false; 
 
    Mock.NonPublic.Arrange(httpRequestCreator, "Create", Arg.Expr.IsAny<Uri>()).DoInstead(() => isCalled = true); 
 
    // Act 
    System.Net.IWebRequestCreate iWebRequestCreate = (System.Net.IWebRequestCreate)httpRequestCreator; 
 
    iWebRequestCreate.Create(new Uri("https://www.telerik.com")); 
 
    // Assert 
    Assert.IsTrue(isCalled); 
}

Note the use of Arg.Expr.IsAny<Uri>() - as we mock a non-public call, we need to know the type of the argument to resolve the method. Thus, instead of using Arg, like we do in most of the other cases, we must use Arg.Expr.

Important

To mock an internal type, your assembly name must be fully qualified according to the framework design rules, i.e. assembly name = namespace. Note that you can't mock types from mscorlib in this way. JustMock does a hierarchical search to find the proper qualified name as in the above example. System.Net.HttpRequestCreator is found in the System assembly, not in System.Net.

Example 15 shows how you can handle an even more complex scenario - mock internal class by calling an original constructor with arguments, then make a call to the original implementation from a public interface. For the purpose of the example, it will be used another internal class - System.Net.WebSocketHttpRequestCreator - derived from the public interface System.Net.IWebRequestCreate.

The sample test verifies whether the call to Create method has been made and the returned Web.WebRequest object has an expected value for RequestUri property set.

Example 15: Complex mocking of internal .NET class with constructor arguments

[TestMethod] 
public void ShouldMockInternaldotNETClassWithArgs() 
{ 
    // Arrange 
    string typeName = "System.Net.WebSocketHttpRequestCreator"; 
 
    var httpRequestCreator = Mock.Create(typeName, (config) => config 
        .CallConstructor(new object[] {true})); 
 
    Mock.NonPublic.Arrange(httpRequestCreator, "Create", Arg.Expr.IsAny<Uri>()) 
        .CallOriginal() 
        .MustBeCalled(); 
 
    // Act 
    System.Net.IWebRequestCreate iWebRequestCreate = (System.Net.IWebRequestCreate)httpRequestCreator; 
 
    var result = iWebRequestCreate.Create(new Uri("https://www.telerik.com")); 
 
    // Assert 
    Mock.Assert(httpRequestCreator); 
    Assert.AreEqual(new Uri("https://www.telerik.com"), result.RequestUri); 
}

Mocking Using a Dynamic Wrapper

JustMock leverages .NET 4 and the DLR to allow you to wrap non-public implementations in dynamic objects and arrange them as naturally as you can do it with public members.

Example 16 shows how to wrap the mock instance in a dynamic object using Mock.NonPublic.Wrap(). The wrapper can be passed to Mock.NonPublic.Arrange and Mock.NonPublic.Assert together with an operation to specify what you want to arrange. You could also arrange:

  • the value of a property getter
  • the action of a property setter

Argument matchers are specified using Arg.Expr.

When using dynamic expressions in Visual C# projects, you should reference the Microsoft.CSharp assembly.

Example 16: Using dynamic wrapper

[TestMethod] 
public void ShouldInvokeNonPublicMemberDynamic() 
{ 
    Foo foo = new Foo(); 
 
    // Arrange 
    dynamic fooAcc = Mock.NonPublic.Wrap(foo); 
    Mock.NonPublic.Arrange<int>(fooAcc.PrivateEcho(Arg.Expr.IsAny<int>())).Returns(10); 
    Mock.NonPublic.Arrange<string>(fooAcc.Value).Returns("foo"); 
    Mock.NonPublic.Arrange(fooAcc.Value = "abc").OccursOnce(); 
 
    // Act 
    var actual = foo.Echo(5); 
    var value = foo.Value; 
    foo.Value = "abc"; 
 
    // Assert 
    Assert.AreEqual(10, actual); 
    Assert.AreEqual("foo", value); 
    Mock.Assert(foo); 
}
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