Add tests

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Add some tests for CI

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For sure:

• [x] Make sure birthday and age in a given month is correct
• [x] Make sure multiple payments are getting included (if active)
• [x] Make sure down payment and monthly payment are split (if appropriate)
• [ ] Add tests to all functions and methods that I've created
• [ ] #18
• [x] Person too old
• [x] Person too young (not born yet, could be typo)
• [ ] Tests looking at savings and retirement before and after retirement date
• [ ] Ensure payments work historically. I.e., if you are 40 and already have a mortgage, that should be handled appropriately.

Maybe:

• [x] Ensure birthday is a date in the correct form

[Skips-Scramble]

So there are a few things going on, or will go on, that I need to pay attention to:

• Need to test the outputs
• Need to test and validate the inputs
  • Inputs can come from a json/dictionary or the web inputs
  • Need to make some sort of CI with test model inputs?
• The tests should hit against some set validations that are stored somewhere that makes sense to hit again json inputs and user inputs
• The validations will also be run during the normal pipeline, so need to be stashed somewhere that can be accessed easily and have many run without having to call a million things (at least, not in the pipeline)