Have some helper functions for tests to reduce repetitive code

[naved001]

We can have a module to have commonly used test functions/fixtures. Like loading and modifying the config file. This is in HIL https://github.com/CCI-MOC/hil/blob/master/haas/test_common.py

This will make tests neater. What are your thoughts? Comment below if you feel we can make some common functions for the tests.