When is a software product "finished"? This all depends on who you're asking and in what aspect. One of the crucial aspects of software houses is testing. Unlike play testing where people have the potential to have fun with the product, software testing is mostly the opposite.
There are several types of software testing, and this article isn't meant to be a definitive guide on how to perform this job, but I will give a quick run down of what it means and what we do.
During any testing, are the proper inputs handled? This should be one of the first questions that arise. Of course, what is good input data, if we can't throw some bad input data in there to spice things up. Data validation is the process of testing software against good, bad, and unknown data. What happens when that 0 or 1 input was actually a -1 as input? Does the program blow up? We won't know unless we test it!
This is basically the smallest form of testing. Do small units of logic perform as expected. This usually means I test a specific function or method and if the resultant output from that logic is what is expected, I could say that this unit test passed -- it performed as expected. This testing is more or less automatically performed by the programmer as code is written, or at least it should be!
Does the software do what it is suppose to do, and do it fast enough? We may make the next best game ever, but if it runs at 8 frames a second... that's probably bad.
This can sometimes go overlooked (especially on Android phones!), does the software work on multiple different configurations? Are there weird effects? Specifically for Android, will the product work on a phone, and an Android tablet?
This is like Software Quality Assurance or Quality Control. Does the software deliver, on a high level, what the design is? Think of this like a marriage of software testing with play testing. Does the product allow the player to actually play the game as designed? Does the code actually allow for the player to launch new marbles and perform all the functions needed to play? If these are both yes, then it passed both the play test, and the software test, this the product can be accepted as the product.
For more information about testing, validation, methods to perform them, etc... really, we encourage you to look at the wikipedia article here: Software Testing. The trick is to find what works for you and use that.