gistfile1.cs

var testHarness = new TestHarness();

var consoleTestProcessor = new ConsoleTestProcessor();
testHarness.Processors.Add(consoleTestProcessor);

var fileSystemTestProcessor = new FileSystemTestProcessor();
fileSystemTestProcessor.AddMockFile(@"c:\foo.txt", "bar");
testHarness.Processors.Add(fileSystemTestProcessor);

var dateTimeProcessor = new DateTimeProcessor(new DateTime(2010, 01, 25));
testHarness.Processors.Add(dateTimeProcessor);

testHarness.Run(() => {
	new Foo().Bar();
});

Assert.AreEqual(@"Fizz
Buzz
FizzBuzz", consoleTestProcessor.OutputText);