How to mock static methods in c using MOQ framework

Question

I have been doing unit testing recently and I ve successfully mocked various scenarios using MOQ framework and MS Test  I know we can t test private methods but I want to know if we can mock static methods using MOQ

User · Answer

Moq cannot mock a static member of a class.

When designing code for testability it's important to avoid static members (and singletons). A design pattern that can help you refactoring your code for testability is Dependency Injection.

This means changing this:

public class Foo
{
    public Foo()
    {
        Bar = new Bar();
    }
}

to

public Foo(IBar bar)
{
    Bar = bar;
}

This allows you to use a mock from your unit tests. In production you use a Dependency Injection tool like Ninject or Unity wich can wire everything together.

I wrote a blog about this some time ago. It explains which patterns an be used for better testable code. Maybe it can help you: Unit Testing, hell or heaven?

Another solution could be to use the Microsoft Fakes Framework. This is not a replacement for writing good designed testable code but it can help you out. The Fakes framework allows you to mock static members and replace them at runtime with your own custom behavior.

User · Answer

As mentioned in the other answers MOQ cannot mock static methods and  as a general rule  one should avoid statics where possible   Sometimes it is not possible   One is working with legacy or 3rd party code or with even with the BCL methods that are static   A possible solution is to wrap the static in a proxy with an interface which can be mocked      public interface IFileProxy           void Delete string path              public class FileProxy   IFileProxy           public void Delete string path                System IO File Delete path                        public class MyClass            private IFileProxy  fileProxy           public MyClass IFileProxy fileProxy                 fileProxy   fileProxy                     public void DoSomethingAndDeleteFile string path                   Do Something with file                                   Delete             System IO File Delete path                      public void DoSomethingAndDeleteFileUsingProxy string path                   Do Something with file                                   Delete              fileProxy Delete path                      The downside is that the ctor can become very cluttered if there are a lot of proxies  though it could be argued that if there are a lot of proxies then the class may be trying to do too much and could be refactored   Another possibility is to have a  static proxy  with different implementations of the interface behind it     public static class FileServices            static FileServices                 Reset                       internal static IFileProxy FileProxy   private get  set             public static void Reset               FileProxy   new FileProxy                       public static void Delete string path                FileProxy Delete path                      Our method now becomes      public void DoSomethingAndDeleteFileUsingStaticProxy string path                   Do Something with file                                   Delete             FileServices Delete path            For testing  we can set the FileProxy property to our mock   Using this style reduces the number of interfaces to be injected but makes dependencies a bit less obvious  though no more so than the original static calls I suppose

User · Answer

Another option to transform the static method into a static Func or Action   For instance   Original code       class Math               public static int Add int x  int y                        return x   y              You want to  mock  the Add method  but you can t    Change the above code to this           public static Func lt int  int  int gt  Add    x  y    gt                        return x   y               Existing client code doesn t have to change  maybe recompile   but source stays the same   Now  from the unit-test  to change the behavior of the method  just reassign an in-line function to it        TestMethod      public static void MyTest                 Math Add    x  y    gt                        return 11               Put whatever logic you want in the method  or just return some hard-coded value  depending on what you re trying to do   This may not necessarily be something you can do each time  but in practice  I found this technique works just fine    edit  I suggest that you add the following Cleanup code to your Unit Test class        TestCleanup      public void Cleanup                 typeof Math  TypeInitializer Invoke null  null           Add a separate line for each static class    What this does is  after the unit test is done running  it resets all the static fields back to their original value   That way other unit tests in the same project will start out with the correct defaults as opposed your mocked version

User · Answer

Moq  and other DynamicProxy-based mocking frameworks  are unable to mock anything that is not a virtual or abstract method   Sealed static classes methods can only be faked with Profiler API based tools  like Typemock  commercial  or Microsoft Moles  free  known as Fakes in Visual Studio 2012 Ultimate  2013  2015    Alternatively  you could refactor your design to abstract calls to static methods  and provide this abstraction to your class via dependency injection  Then you d not only have a better design  it will be testable with free tools  like Moq   A common pattern to allow testability can be applied without using any tools altogether  Consider the following method   public class MyClass       public string   GetMyData string fileName                string   data   FileUtil ReadDataFromFile fileName           return data            Instead of trying to mock FileUtil ReadDataFromFile  you could wrap it in a protected virtual method  like this   public class MyClass       public string   GetMyData string fileName                string   data   GetDataFromFile fileName           return data             protected virtual string   GetDataFromFile string fileName                return FileUtil ReadDataFromFile fileName             Then  in your unit test  derive from MyClass and call it TestableMyClass  Then you can override the GetDataFromFile method to return your own test data   Hope that helps

[c#] How to mock static methods in c# using MOQ framework?

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