add unit tests suite

[ismael-mendoza]

Following #158, we will have a new MultiCAM model that covers some corner cases we encountered as we were investigating adding merger information in #153. It would be good to add these unit tests to a pytest suite which could aid future model alterations or evaluation other new models.

• identify useful diagnostics in diagnostic notebooks from cleanup and update model #158
• wrap them around pytest with reasonable thresholds for tolerance