[Nmock-general] Fix for the ever-expanding AppDomain bug

[Jim A. <JA...@th...>]

One of NMock's more subtle 'features' is that every time you create a new
DynamicMock instance, a brand new dynamic assembly is created containing
the mock type.  This assembly is not reused, and neither are the mock
types, so the following:

new DynamicMock(typeof(IThingy));
new DynamicMock(typeof(IThingy));

results in two new assemblies, each containing one identical class.  The
problem is that assemblies are never unloaded from a live AppDomain, so for
long-lived domains (ie NUnit test runs), NMock keeps chewing up memory.

I've attached a fix for this (source files only - you'll need to include
the new files in the correct VS projects).  It involves 1) making the
assembly (the ModuleBuilder, to be specific) static, so we can reuse it
throughout the entire test run, and 2) caching mock types, so we never
create two identical mock types for the same parent type.

Putting this fix in resulted in a ~50% reduction in memory and a ~10%
increase in speed for us (that's for ~2000 tests).

Jim

(See attached file: MockTypeIdentifier.cs)(See attached file:
ClassGenerator.cs)(See attached file: MockTypeIdentifierTest.cs)(See
attached file: ClassGeneratorTest.cs)