If JAVA_HOME is not set, the Plexus JavacCompiler will fallback to "which javac". However, this statement is logged without a proper check that checks whether logging is enabled (see my pull request https://github.com/codehaus-plexus/plexus-compiler/pull/52 ). Because Shrinkwrap does not attach a logger to the JavacCompiler, and this issue in Plexus Compiler, the JavacCompiler will throw a null pointer exception during compilation causing the test run to fail.

I've already proposed a PR to Plexus Compiler, but perhaps it is a good idea to attach a logger anyway so that compilation output can be printed to the logging output, which will also resolve this issue.