Document extension method shimming

[Miista]

Please refer to tonerdo/pose#22

I will add tests to ensure that we continue to support this.

• Add tests (see below)
• Update README with example

Tests

Defined using	Called using	Expected result
Static method invocation	Static method invocation	✔️
Static method invocation	Extension method invocation	✔️
Extension method invocation	Static method invocation	✔️
Extension method invocation	Extension method invocation	✔️

[Miista]

I can confirm that we do support shimming extension methods. Please see the following MVE:

public static class IntExtensions
{
    // The extension method defaults to stringifying the int
    public static string GetFunnyName(this int i) => i.ToString();
}
    
public class Program
{
    public static void Main(string[] args)
    {
        var extensionShim = Shim
            .Replace(() => IntExtensions.GetFunnyName(Is.A<int>()))
            // We overwrite the extension method to simply return "H"
            .With(delegate(int i) { return "H"; });
                
        PoseContext.Isolate(()=>
        {
            var i = 0;
            Console.WriteLine(i.GetFunnyName());
        }, extensionShim);
    }
}

Please note that the shim can be defined in one of the following ways.

Static method invocation

Shim
    .Replace(() => IntExtensions.GetFunnyName(Is.A<int>()))
    .With(delegate(int i) { return "H"; });

Extension method invocation

Shim
    .Replace(() => Is.A<int>().GetFunnyName())
    .With(delegate(int i) { return "H"; });