So for this year's Advent calendar I'll focus on a made up file utility object. The object is called FileUtil and it implements an interface called IFileUtil which looks like this:

    public interface IFileUtil
    {
        void Create(string content);
        void Delete();
        string Read();
        string Path { get; }
        bool Readable { get; set; }
    }

I think the methods are quite straight forward but a quick walk-through:

• Create creates a file with given content.
• Delete deletes the file.
• Read returns the content of the file.
• Path returns the path to the file.
• Readable indicates if the file is readable or not. It is also possible to change permissions (i.e. readable or not) using this property.

The test I will write (in 24 different ways) is a test where I want to verify that the correct exception is thrown when I try to read a file that is not readable. And before I do that I want to make sure the file actually exists and is readable. So basically the test consist of the following steps:

• Create a test file.
• Make sure I can read that file.
• Change the file from readable to not readable.
• Make sure I can no longer read the file.
• Remove the test file.

All the tests are written using Xunit.net