Comparing Discriminated Unions

Question

I'm a newbie to F# and I'm playing around with FParsec. I would use FParsec to generate an AST. I would like to use FsUnit to write some tests around the various parts of the parser to ensure correct operation.

I'm having a bit of trouble with the syntax (sorry, the exact code is at work, I can post a specific example later) so how exactly could one compare two discriminated unions (one the expected, the other the actual result)? Could someone provide a tiny code example using FsUnit (or NUnit), please?

An example discriminated union (very simple)

type AST = 
    | Variable of string
    | Class of string
    | Number of int