private static void generateClass(Filer filer, String generatedClassName) {
    PrintWriter writer = null;
    try {
      writer = new PrintWriter(filer.createSourceFile("test." + generatedClassName).openWriter());
      writer.println("package test;");
      writer.println("public class " + generatedClassName + " {}");
    } catch (IOException e) {
      throw new RuntimeException(e);
    } finally {
      if (writer != null) {
        writer.close();
      }
    }
  }
Tests that a {@link ProcessingStep} passed to {@link
BasicAnnotationProcessor#asStep(ProcessingStep)} still gets passed the correct arguments to
{@link Step#process(ImmutableSetMultimap)}.
common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java