TDDBilling

My take on a Test Driven Development exercise using a simple billing system feature set.

Using red/green/refactor cycle:

1. First write a failing test,

2. Then write the minimal feature code to pass the test,

3. Finally refactor and clean up the codebase.

Repeat this till all the features are complete and tested working.

Basic billing system features:

1. Monthly billing

2. Grace period for missed payments (dunning status)

3. Not all customers are subscribers

4. Idle customers should be automatically unsubscribed