Add two tests for Flask.

[barik]

Add two tests for flask. The first test is test_syntaxerror_request that shows what MACER would return on a program with an syntax error. The second test is test_noerror_request, that shows what MACER would return with no errors.

You can use:

pytest --disable-pytest-warnings .\test_server.py

to run the tests. The --disable-pytest-warnings is there to suppress TensorFlow deprecation warnings.

The branch name is tbarik/unittest.