Test jobs do not run on a cluster or in any distributed context. Instead, they are executed immediately on the machine which hosts the WebMapReduce server, inside an environment that emulates the map-reduce process. This allows output to be delivered quickly, and also allows for more helpful error output. The purpose of test jobs is to provide an easy way for users to debug their programs without having to write a test framework of their own. In general, jobs should be tested in the test environment before being run full-scale in order to save time and resources.

Note that the output of test jobs is never saved, and additionally there is a limit on the size of input that may be used with test jobs. Since this limit is configurable, questions concerning test job input size should be directed to local system administrators.