Use Moq to mock extension methods
In unit testing scenarios, it may be necessary to mock extension methods applied to existing interfaces. Consider the following:
public interface ISomeInterface { void SomeMethod(); } public static class SomeInterfaceExtensions { public static void AnotherMethod(this ISomeInterface someInterface) { // 方法实现 } } public class Caller { private readonly ISomeInterface someInterface; public Caller(ISomeInterface someInterface) { this.someInterface = someInterface; } public void Main() { someInterface.AnotherMethod(); } }
In order to test the Caller
class, you need to mock the ISomeInterface
interface and verify calls to the AnotherMethod
extension methods. However, trying to simulate x => x.AnotherMethod()
directly produces the exception:
[Test] public void Main_BasicCall_CallsAnotherMethod() { // Arrange var someInterfaceMock = new Mock<ISomeInterface>(); someInterfaceMock.Setup(x => x.AnotherMethod()).Verifiable(); // 这里会抛出异常 var caller = new Caller(someInterfaceMock.Object); // Act caller.Main(); // Assert someInterfaceMock.Verify(); }
Exception information:
<code>System.ArgumentException: Invalid setup on a non-member method: x => x.AnotherMethod()</code>
To solve this problem, one way is to create a wrapper object for the extension method:
public class AnotherMethodWrapper { public static void CallAnotherMethod(ISomeInterface someInterface) { someInterface.AnotherMethod(); } }
In tests, wrapper methods can be mocked:
[Test] public void Main_BasicCall_CallsAnotherMethod() { // Arrange var wrapperMock = new Mock<AnotherMethodWrapper>(); wrapperMock.Setup(x => x.CallAnotherMethod(It.IsAny<ISomeInterface>())).Verifiable(); var someInterfaceMock = new Mock<ISomeInterface>(); // 这里需要调整Caller的构造函数,注入wrapperMock.Object // 这部分需要根据实际情况修改,可能需要修改Caller类或者使用其他方法注入依赖 var caller = new Caller(someInterfaceMock.Object); // 此处可能需要修改,注入wrapperMock.Object // Act caller.Main(); // Assert wrapperMock.Verify(); }
By using wrappers, extension method calls can be mocked and unit tested. It should be noted that the Caller
class in this example needs to be modified to use AnotherMethodWrapper
. This depends on the specific implementation of the Caller
class, which may require dependency injection or other methods to inject AnotherMethodWrapper
into Caller
.
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