NUnit / DotCover successful exit code for failed tests

I have a build step that runs my NUnit tests as well as DotCover. However, I'm noticing that even when a test fails, the exit code of the step is successful (zero).

My build will actually fail because the test fails, but the step does not. The problem is that I don't want the next step to take place if a test fails, but it is.

Thanks in advance,

Levi