Currently, if you do a successful build and then try to run run-javascriptcore-tests as one would do on Mac, it will show all the tests as regressions. This is because testkjs needs the ICU, etc. dlls to be in the WebKitBuild\bin directory, but they currently are not copied there. I would suggest that after the build step in run-javascriptcore-tests, it should either copy over the DLLs from Safari into WebKitBuild\bin, or use that special magic that makes DYLD_LIBRARY_PATH work on Windows. If that would be difficult to implement properly, as an alternative, run-javascriptcore-tests could check to see if the DLLs are missing and report it to the user so that there's some indication of the problem.
You also need to do this to get run-webkit-tests working