You can merge two or more coverage files by simply calling the program with the paths you want to look for coverage files in. Folders and files can be mixed. If a directory is used, it must not contain JSON files with contents other than testwise coverage.
To build the executable jar file, you can use mavan package:
mvn package
Example Call:
java -jar testwise-coverage-converter-0.1.jar /path/to/testwise/coverage
For big coverage files this can be quite memory hungry since it keeps all coverage files in memory for some time so be sure to give java enough memory for your testwise coverage files.
The resulting coverage will be written into the file out.json in your current working directory.