Bugs in Windows Application Development

Today I at last have found time to fix some long-lasted bugs in one of my programs. Some of these bugs have been annoying users for about one year. They inconspicuously appeared after some phase of editing of source code. During fixing, I found two other previously completely overlooked bugs. They are not critical in nature, but annoying. It seems that this process (of finding and fixing bugs) can last forever. Development for Windows OS, comparing to development for microcontrollers, allows you to employ many ready-to-use system (as well as third-party) libraries, thus freeing you from the task of implementing service code for yourself, but at the same time, bugs and inconsistencies in system and third-party libraries can force you to spend much time in efforts to figure out why your application is not behaving as you expected, and I'm pretty tired of it. Conclusion is to test as big fraction of program's functionality as possible after every source code change.