Richie Lee shows how to use TestContext.WriteLine to debug MSTest runs:
Unit testing can sometimes throw up unexpected issues that are entirely concerned with the unit tests and not the application under test. Recently I’ve been having issues with DateTime formats affecting the results of the unit tests: the format of the DateTime was different on the build server than it was on my local machine. The stored procedure could not be altered (because reasons*). The datetime formats on both SQL and Windows were identical to my machine, and running the test itself on the build box caused the test to go green, so clearly there was something funky going on in the build process. SO I needed to find a way of logging the values during the process to verify where the issue was. And, as luck would have it, MSTest has such a method to help you. First create a private instance of the TestContext object in the TestClass, then you create a public property.
This turns out to be really easy to do.