@Override
    public void evaluate() throws Throwable {
      File tmpDir = File.createTempFile("OverridesTest", "dir");
      tmpDir.delete();
      tmpDir.mkdir();
      File dummySourceFile = new File(tmpDir, "Dummy.java");
      try {
        Files.asCharSink(dummySourceFile, UTF_8).write("class Dummy {}");
        evaluate(dummySourceFile);
      } finally {
        dummySourceFile.delete();
        tmpDir.delete();
      }
    }
An equivalent to {@link CompilationRule} that uses ecj (the Eclipse compiler) instead of javac.
If the parameterized test is not selecting ecj then this rule has no effect.
common/src/test/java/com/google/auto/common/OverridesTest.java