I know, testing sequentially takes up loads of time. And the board, the shareholder, your colleagues, your boss, they all want results now. And I really understand them. So how do I like to solve this dilemma.
2. Do the quick wins first so you can show measurable results to your stakeholders
3. Ignore the small stuff (fill ins and hard slogs)
3. Allow yourself time for the major projects, and execute them properly and without interference from the small stuff
This usually prevents teams or individuals from trying everything at the same time. I prefer to have a ratio of 1 to 5. One big long term project that does not reap results immediately on five medium or short term projects.