I understand why you made this change for a JUnit test class with a single @Test method. However, calling configure and close prevents one from calling configure once in a @BeforeClass method and testing several (key, value) pairs in a series of separate @Test methods using the same static Mapper or Reduce instance. This more closely mirrors what the actual mapreduce does and allows one to make sure they are properly clearing state between different (key, value) pairs.
This change also makes 0.8.x non backwards compatible with mapreduce jobs that test with mrunit 0.5.0 since you will call configure again with an empty Configuration object after we already called it.
Maybe you could make calling configure and close configurable by us providing a boolean in a constructor to indicate whether you should call configure and close