Testing deserves and requires it's own spot in the development plan. It is understandable to only plan ahead sparingly, because many developers dislike testing. They tend to test gently, subconsciously knowing where the code will break and avoiding the weak spots. However, with the proper training and setup, you can find your bugs now and not later.
Finding bugs is somewhat like fishing with a net. At 200ok, we use fine, small nets (unit tests) to catch small fish, and big, coarse nets (integration tests) to catch the killer sharks.
We encourage you to start testing as soon as you have code.