These tests are in a separate package because they depend on both msdk-spectra-spectrumtypedetection and msdk-io-mzml modules. If we add the tests to the msdk-spectra-spectrumtypedetection module, it would create a dependency cycle.
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window msdk-spectra-spectrumtypedetectiontest-0.0.6.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.