I find demo for MeediaMuxer, which is a AndroidTestCase File. Here is the link.
I never used Android Test. I did some research, but most of them are somehow a little complex... It seems like that I need a xml file, a java file for TestSuite and a java file for AndroidTestCase. And now I have the AndroidTestCase, could anyone tell me how to write the TestSuite? Thank you!
From TestSuit overview
Android provide a pretty good documentation for that, tell me if you have more questions after reading it.
Also here is the official article about testing in Android.