Check exercise specific tests

[LottaMe]

Depends on Check whether exercise compiles

Description

Pylet should check exercise specific tests after it sees whether the exercise compiles (if there is an exercise specific test file), to check if the user is solving the correct problem in the exercise. If the test fails, it should return a helpful error message. As well as the information that the exercise has failed, but compiles. If the test passes, it should go to the previously defined success process.

EDIT: TO MAKE IT EASIER THE TESTS CAN BE IN EXERCISE FILE

Checklist

• [ ] create exercise test file (and figure out where it goes in folder structure)
• [ ] pylet should check whether there is a test file for the exercise
• [ ] pylet should run tests if compiler passes
• [ ] pylet should output helpful error message if test fails
• [ ] pylet should go to success process if test succeed

[LottaMe]

Before finishing this, the project structure needs to be changed, so it depends on #13