CompareSizeForCompressor was not in class "TestMakeApk", so we can't use "self.assertTrue" directlly.
We can transfer "self.assertTrue" as a parameter to CompareSizeForCompressor():
def CompareSizeForCompressor(mode, original, ext, name, fun):
  fun(compressed_size < size)

def testCompressor(self):
  fun = self.assertTrue
  CompareSizeForCompressor('all', css_file, 'css', name, fun)