Writing .NET code analysis rules as unit tests

Writing assembly usage rules as unit tests turns out to be unexpectedly simple:

[Test]
public void Immutable_Types_Should_Be_Immutable()
{
  var decorated = GlobalSetup.Types
    .Where(t => t.Has<ImmutableAttribute>());

  foreach (var type in decorated)
  {
    var count = type.GetAllFields().Count(f => !f.IsInitOnly && !f.IsStatic);
    Assert.AreEqual(0, count, "Type {0} should be immutable", type);
  }
}

This test (based on the functionality provided by the Lokad.Quality.dll from the Shared Libraries) does the job, but it is not logically a proper one, yet.

Proper test should dynamically emit one test case per type tested (something to be done through the NUnit extensibility model).

How do you define and enforce high-level coding rules in your projects?