So I wrote these E2E tests to test my credit card expiration notification emails. So I wrote my code, and tested it. Tests failed. I spent the next 6 hours (spanning 2 days) debugging my tests. Come to find out that the tests were fine all along. The issue was my code.

Apparently everything has dates starting at 1 (day starts at 1, year starts at 1). But MONTHS. Months start at 0