I ran into a need to test some functionality that relies on system
properties. Writing the test was error-prone because the properties persist
across the jvm so if you set them in a test they leak across to other tests
unless you are careful about @After methods. It occurred to me it would be
nice if LuceneTestCase would detect this and yell. It could save all the
system properties before each test (or at least each test class) and see if
they are restored at the end.  I don't know if this arises much in Lucene,
but maybe in Solr?