Unit tests should clean up output

[davidzchen]

With #255, unit tests are now being run at build time. However, most tests are writing output files in the current working directory (which is the root of the subproject) and not cleaning up the output files.

.gitignore files have been added so that the test output files will not be accidentally checked into source control. However, this is a stop-gap. The large numbers of test output files hinder navigation through the source tree.

The tests that are polluting the source tree should be updated so that they use an isolated working directory and clean up their output files when they exit.