I have the following:
using System;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using NUnit.Framework;
using Selenium;
using System.Collections.Generic;
but still can not get CollectionAssert which I found on CollectionAssert (NUnit 2.4)
The printscreen:

It’s definitely in the
NUnit.Frameworknamespace in thenunit.frameworkassembly – I’ve just downloaded NUnit 2.5.10 to check.I suggest you check which version of
nunit.frameworkyou’re really referencing, and open it up in Reflector to check for the existence ofCollectionAssert.