replacing 20 amp breaker which is the test breaker
If the breaker is over 5 years old it is a GFCI breaker and it protects outlets at wet locations whether they are outside or at a sink in the kitchen or bath. Make sure you replace it with the same style (GFCI) Also make sure it is bad to begin with by pressing the test button and if the reset button pops out, it is good, press the reset button to turn the breaker back on. This confirms it is good. OR it might already be tripped and just needs to be reset. If pressing the test or reset does nothing, then the breaker needs replacing. If you have never been inside a breaker box, it is a scary proposition for a newbie, I would not recommend it. Please test it to see if it is bad by the instructions above, and get somebody who has done it before to replace it while you watch perhaps....