c# - Extension methods conflict

Question

Lets say I have 2 extension methods to string, in 2 different namespaces:

namespace test1
{
    public static class MyExtensions
    {
        public static int TestMethod(this String str)
        {
            return 1;
        }
    } 
}

namespace test2
{
    public static class MyExtensions2
    {
        public static int TestMethod(this String str)
        {
            return 2;
        }
    } 
}

These methods are just for example, they don't really do anything.

Now lets consider this piece of code:

using System;
using test1;
using test2;

namespace blah {
    public static class Blah {
        public Blah() {
        string a = "test";
        int i = a.TestMethod(); //Which one is chosen ?
        }
    }
}

The Question:

I know that only one of the extension methods will be chosen.
Which one will it be ? and why ?

Edit:

This also bothers me, but not as much because it's a static method in a static class after all:

How can I choose a certain method from a certain namespace ?
Usually I'd use Namespace.ClassNAME.Method() ... But that just beats the whole idea of extension methods. And I don't think you can use Variable.Namespace.Method()

Answer 1

No method will be chosen: the call is ambiguous and will not compile.

Why can't you do Namespace.ClassNAME.Method()? Certainly there is nothing that prevents you from treating extension methods as normal static methods, and in fact this is the only way for you to fix the ambiguity and have the program compile.