If you’re using TestDriven.Net 2.23 on a 64-bit OS, you should find that running tests is almost twice as fast!
It turns out that the JIT compiler for x64 is considerably slower than for x86 (and uses more memory). You can easily improve the startup time for your EXE projects by changing them to compile for x86. In fact this is what Microsoft is doing in Visual Studio 2010 (the default for EXEs will be x86). It’s only worth compiling EXEs for AnyCPU if your application might use a lot of memory. See Rick Byers’ post on the subject: AnyCPU Exes are usually more trouble than they're worth.
For this reason the default for AnyCPU test projects is now to execute in a 32-bit (WOW) process. If you need to temporarily run tests in a 64-bit process, there’s an option to change the default.
If you have tests that check behavior in a 64-bit process, you can add them to a test project that compiles for the x64 platform.
Because this is a significant change, I thought it warranted its own post. There’s a lot more in this release that I’m planning to blog about later.