create a testing file

[rkoudsi]

1. create a new file "tests.py". This new file will hold all of our testing for our program.
2. Move our current testing function test_roll to this new file
3. At this point, test_roll will not work a. It will try to find roll but doesn't know where to look b. Fix this by at the top of the file adding import Introduction to import functions from the file "Introduction.py"

[rkoudsi]

This relies on completion of #6 first