Automate APK testing

I generally get an Android app to test. Let's say, an app which take two inputs and generate an output based on some algo. I want to automate the testing, where I can provide around 100 different sets of input and print the result may be in form of logs. I don't get the code of application from Dev team, just the APK to install. Please suggest best way to automate the testing. I'm familiar with Java.