Using pip-tools to fix requirements.
Add packages in requirements.in then run pip-compile and pip-sync.
To run the tests, a minimum of environment variables must be set. Copy .env.sample to .env to run.
We cannot keep a real .env file checked in as it would override the Heroku environment variables in production.
Note: the REWARD_PUBLIC_KEY must not be changed as it matches the set json fixtures for horizon responses and changing it would fail the tests.