Mono and Extension Methods with MonoDevelop 2.8.5 - mono

Question

I have written a unit test with MD 2.8.5 in a project that includes System.Core and with build target Mono/.NET 3.5. I really like the Assert.Throws of the newer NUnit, so decided to write an extension method for it. I created a new file with this as its content in the same namespace as the test. Can anyone see my error?
public delegate void TestDelegate();
public static class AssertThrows
{
public static T Throws<T>(this Assert assert, TestDelegate td)
where T : Exception
{
try
{
td();
}
catch(T e)
{
return e;
}
catch
{
throw new AssertionException("Wrong exception type.");
}
throw new AssertionException("Did not throw an error.");
}
}
MonoDevelop "sees" the extension method through its code completion. However, the compiler reports:
Performing main compilation...
/Users/shamwow/dev/EngineTests.cs(19,37): error CS0117:
`NUnit.Framework.Assert' does not contain a definition for `Throws'
/Applications/MonoDevelop.app/Contents/MacOS/lib/monodevelop/AddIns/NUnit/nunit.framework.dll (Location of the symbol related to previous error)
Build complete -- 1 error, 0 warnings
(I know MD and Mono are not the same.)

Answer 1

I assume you're trying to use it just as:
Assert.Throws<FooException>(() => ...);
Extension methods don't work like that - they appear to be instance methods on the extended type. As you won't have an instance of Assert, you can't call your extension method like that.