When using WebAPI inside a test fixture make sure you shutdown the HttpSelfHostServer instance correctly or your tests will more than likely fail when run from a continuous testing framework like nCrunch. See this post for info about using the self hosting version of WebAPI inside a test fixture. So my tests were running successfully when run inside Visual Studio from either the inbuilt runner or via Reshaper, but were failing when run from nCrunch: The failing tests weren't consistent either, sometimes none would fail, sometimes a couple, sometimes all... What the tests had in common was they were using a shared resource setup inside the test fixture setup method - this is like the setup method for a test but scoped at the class (test fixture) level. The setup was failing randomly were it was setting up the WebAPI self host - see highlighted yellow area, you can see the failing icon for nCrunch at the side: The exception was telling me it was trying to crea...