Add unit tests

[sciurus]

• incident_acknowledged_or_resolved needs tests to validate it handles input appropriately.
• components_with_incidents needs stubbed get_acknowledged_incidents to test different scenarios around incidents with and without component tags
• components_and_incidents needs stubbed get_incidents to test different scenarios around incidents we did and didn't create
• open_incident and close_incident need mocked _created_incident and _update_incident to test they're calling them with the correct arguments (e.g. chose the right template and appended watermark)
• sync needs stubbed components_with_incidents + components_and_incidents and mocked close_incident + open_incident to ensure the latter are called correctly for different combinations of statuspage and pagerduty incidents