Not a good idea. The tests are run at deployment, but what if someone deletes that directory later? Then your application doesn't work correctly anymore.

You are optimizing at the wrong place. That directory test costs you about 30 bytes of hard disk space and about 100 microseconds per run of your application (probably less since the directory is accessed later on). If you think this is wasted time and space, you should switch to machine language programming.

I just wrote a script last week where I tried to test everything twice if possible so as to make sure no error condition escaped unnoticed. It was a script to format and fill a SD-card, so for example I had two different ways to get the size of the device, just to be sure I don't make a mistake here.

As long as tests are not in time-critical parts of your application, they are your best friends, an asset and a pillow for a peaceful sleep.