<merge>/merge — offline meta- and runtime coverage data compressor.
<merge>/merge is EMMA's offline meta- and runtime coverage data compressor. It reads in an arbitrary number of data files containing class metadata and/or runtime coverage data and compresses all of it into a single session data file.
Why merge? Despite the fact that all other EMMA tools can do in-memory merging of an arbitrary number of input data files, there are valid reason for using <merge>/merge tool:
Coverage metrics for a particular application could be determined by a large set of meta- and runtime coverage data files, not necessarily collected in a single application run. For example, a Swing client could run in one JVM and a remoted server in another, possibly on a different host machine. Or a testsuite could be spread over a sequence of forked JVM processes.
Collecting all EMMA data in a single file could be a simple matter of convenience: such a coverage session data file is a memento of a particular state of application coverage. Such a session data file contains all the data necessary to regenerate all coverage reports (for source code embedding in a coverage report you also need to preserve the particular versions of sources used at the instrumentation time: a source revision control system is a good solution for this).