Mock Concrete FileInfo Object

Question

I would like to Mock the System.IO.FileInfo.Extension Method and have it return ".xls" but I can't get anything to work

This Example works great for Delete but not for Extension (The code will not compile)

  [ClassInitialize]
      public static void Initialize(TestContext context)
      {
         Mock.Partial<FileInfo>().For((x) => x.Extension);
      }

I Have also tried using this example but the code is wrong.

• I have a fully licensed copy of JustMock
• I am using VS 2010 .net 4.0

Edit: I know I can setup a interface and test that way, but the paid version JustMock is supposed to mock concrete classes. Since I paid for it, I would like to know how to do it that way.

Answer 1

With the latest release of JustMock (Q2 2012). You no longer need the MockClassAtriibute for mocking MsCrolib members.

You can write above test very much in the following way:

[TestClass]
public class UnitTest1
{
        [ClassInitialize]
        public static void Init(TestContext context)
        {
            Mock.Replace<FileInfo, string>(x=> x.Extension).In<UnitTest1>();
        }


       [TestMethod]
       public void ShouldAssertFileInfoExtension()
       {
           var fileInfo = Mock.Create<FileInfo>(Constructor.Mocked);

           string expected = "test";

           Mock.Arrange(() => fileInfo.Extension).Returns(expected);

           Assert.AreEqual(fileInfo.Extension, expected);
       }
}

Answer 2

It sounds to me like you just need to abstract that dependency into another wrapper class and then it would be easy to mock.

 public class FileInfoAbstraction
 {
      protected FileInfo _fileInfo = null;

      public virtual string Extension
      {
          get { return _fileInfo.Extension; }
      }

      public FileInfoAbstraction(string path)
      {
          _fileInfo = new FileInfo(path);
      }
 }

Then, wherever you were using the FileInfo class, insert your abstraction:

 var myFileInfo = new FileInfoAbstraction(somePath);

Because the extension is marked as virtual now, most mocking frameworks will be able to modify it.

Answer 3

Guess I was missing an attribute

[TestClass, MockClass] // **MockClass Added**
public class UnitTest1
{
        [ClassInitialize]
        public static void Init(TestContext context)
        {
             Mock.Partial<FileInfo>().For<FileInfo, string>(x => x.Extension);
        }


       [TestMethod]
       public void ShouldAssertFileInfoExtension()
       {
           var fileInfo = Mock.Create<FileInfo>(Constructor.Mocked);

           string expected = "test";

           Mock.Arrange(() => fileInfo.Extension).Returns(expected);

           Assert.AreEqual(fileInfo.Extension, expected);
       }

}