When analyzing code coverage in Hadoop Core, we noticed that some coverage gaps are caused by the way the coverage calculation is done currently. More specifically, right now coverage can not be calculated for the whole Core at once, but can only be calculated separately for top level modules like common-project, hadoop-hdfs-project etc.
At the same time, some code in particular modules is tested by tests in other modules of Core. For example, "org.apache.hadoop.fs" from hadoop-common-project/hadoop-common is not covered there but it's covered by tests under hadoop-hdfs-project.
To enable calculation of "cumulative" code coverage it's needed to move Clover profile definition up one level, from hadoop-project/pom.xml to the top level pom.xml (hadoop-main).
Patch both for 0.23 and 2.x will be attached shortly.