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Moq Documentation

repository·main·Indexed 27 days ago

https://github.com/devlooped/moq

A type-safe mocking library for .NET that uses LINQ expression trees to set up dependencies, define behaviors, and verify interactions in unit tests. It supports mocking both interfaces and classes, provides granular control via MockBehavior, and includes support for events, out/ref arguments, and COM interop types via Moq.Types.ComTypes.dll.

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What's inside Moq

  1. Overview of Moq.Types.ComTypes.dll

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    The Moq.Types.ComTypes.dll assembly contains Component Object Model (COM) interop types. It is specifically designed to test various aspects of Moq's compatibility with COM. The assembly is generated from the ComTypes.idl definition file located in the same directory.

  2. Moq Core Features

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    Moq provides several advanced features for .NET testing:

    • Strong-typed: Uses expression trees instead of strings for expectations.
    • Mock both interfaces and classes: Supports both types.
    • MockBehavior: Granular control over mock behavior via the MockBehavior enumeration.
    • Override expectations: Set default expectations in a fixture and override them in specific tests.
    • Constructor arguments: Pass arguments to the constructor of mocked classes.
    • Events: Intercept and raise events on mocks.
    • out/ref support: Intuitive support for out and ref arguments.

  4. Build Moq.Types.ComTypes.dll

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    You can build the COM interop assembly by running the BuildDLLFromIDL.cmd batch file in the directory, or by manually executing the MIDL and TLBIMP commands.

    Requirements

    To build the DLL manually, you must have the following tools available in your PATH (e.g., via a Visual Studio Developer Command Prompt):

    • midl (Microsoft's MIDL Compiler): Part of the Windows SDK; used to produce a Type Library from an .idl file.
    • tlbimp (Microsoft's .NET Framework Type Library to Assembly Converter): Part of the .NET Framework SDK; used to produce a COM interop assembly from a Type Library.
    • peverify (Optional): Part of the .NET Framework SDK; used to verify the generated assembly.
    :: Option 1: Run the provided batch file
BuildDLLFromIDL.cmd

:: Option 2: Manual steps

:: 1. Create a COM Type Library (.tlb) from the .idl definition
midl.exe /mktyplib203 ^
         /env win32 ^
         /tlb ComTypes.tlb ^
         ComTypes.idl

:: 2. Convert the type library to a .NET interop types assembly
tlbimp ComTypes.tlb ^
       /out:Moq.Tests.ComTypes.dll ^
       /namespace:Moq.Tests.ComTypes ^
       /keyfile:..\..\Moq.snk ^
       /asmversion:4.0.0.0

:: 3. (Optional) Verify the generated assembly
peverify Moq.Tests.ComTypes.dll

  5. Use Linq to Mocks with Mock.Of<T>

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    For a more succinct syntax, use Mock.Of<T> to create a mock whose behavior matches a lambda expression. This is useful for state-based testing. If you need to verify interactions on a mock created this way, use Mock.Get(instance) to retrieve the mock controller.

      // Create a mock where DownloadExists returns true for "2.0.0.0"
  ILoveThisLibrary lovable = Mock.Of<ILoveThisLibrary>(l =>
    l.DownloadExists("2.0.0.0") == true);

  // Exercise the instance
  bool download = lovable.DownloadExists("2.0.0.0");

  // Assert the state
  Assert.True(download);
  
  // Verify the interaction
  Mock.Get(lovable).Verify(library => library.DownloadExists("2.0.0.0"));

  6. Use the Mock<T> class to set up expectations

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    To create a mock, instantiate Mock<T> where T is the interface or class you want to mock. Use .Setup() to define behavior for specific method calls and .Returns() to specify the return value. Access the actual instance implementing the interface via the .Object property. You can use .Verify() to ensure a method was called with specific arguments and frequency (e.g., using Times.AtMostOnce()).

      var mock = new Mock<ILoveThisLibrary>();

  // Set up a method to return true for a specific input
  mock.Setup(library => library.DownloadExists("2.0.0.0"))
      .Returns(true);

  // Use the Object property to get the instance
  ILoveThisLibrary lovable = mock.Object;
  bool download = lovable.DownloadExists("2.0.0.0");

  // Verify the method was called with the expected value at most once
  mock.Verify(library => library.DownloadExists("2.0.0.0"), Times.AtMostOnce());