I got some problem. I work on some company maintaining web application. Every time I add some feature I often accidentally break other features. I read about testing (unit test, integration testing, etc) and ask my project manager and CTO to implement test on our web application but they refused it. The reason is because the web application is already large and it will take a long time to implement. Actually maintain this application is very stressful because it takes along time to add new feature and every time I break something either CEO or Client will scold me. Do you guys have idea/solution to solve this problem?