The layout test looks for files which are required, or common. Missing about.html files are considered blocking defects (for a release). Missing properties files indicates that strings are not externalized. Or, either of these may indicate a mistake in the build.properties file. The test for class or jar files is meant as a sanity check that the build worked as expected. There are many cases, though, where it is expected to have no class or jar files, in which case the bundle needs to be added to an explicit list of exceptions