code: @Test public void shouldDetectIncrementalChange() throws Exception {
    victim=new Wro4jMojo(){
      @Override protected WroManagerFactory getManagerFactory(){
        return new WroManagerFactoryDecorator(super.getManagerFactory()){
          @Override protected void onBeforeBuild(        final Builder builder){
            builder.setHashStrategy(mockHashStrategy);
          }
        }
  ;
      }
    }
  ;
    setUpMojo(victim);
    final String hashValue="SomeHashValue";
    when(mockHashStrategy.getHash(Mockito.any(InputStream.class))).thenReturn(hashValue);
    when(mockBuildContext.isIncremental()).thenReturn(true);
    when(mockBuildContext.getValue(Mockito.anyString())).thenReturn(hashValue);
    victim.setIgnoreMissingResources(true);
    assertTrue(victim.getTargetGroupsAsList().isEmpty());
    when(mockHashStrategy.getHash(Mockito.any(InputStream.class))).thenReturn("TotallyDifferentValue");
    assertFalse(victim.getTargetGroupsAsList().isEmpty());
  }
  