The files in this and all subdirectories are test suites together with input and output files for use with texttest (http://www.texttest.org). To keep the tests as close to the real input and output as possible, only few of them contain separate license info but all should be considered to be distributed under the same license as the SUMO source code (EPL-2.0). To extract a single test without using texttest use the script <SUMO_HOME>/tools/extractTest.py which accepts the full path to the test to extract as an argument. It requires SUMO_HOME to be set correctly and the binaries in SUMO_HOME/bin.
Please feel free to add and / or modify files here but keep in mind that EPL requires that "derivative works" be licensed under the terms of the EPL. If the extension is a separate module and is not published under the EPL it will not be adopted in the SUMO mainline repository.
Modifications to all the test input files in the SUMO repository and releases are considered derivative work but you may (and should) of course add your own tests.