edge case city: requirements and testing dates for HR business logic
We have an internal application that does staffing, time entry, and now Paid Time Off (PTO) accrual, scheduling and management. It is quite nice, as it has replaced three existing systems, and replaced a number of manual, tedious tasks. I started it last year, as our current system was very inefficient. It was a simple Ruby on Rails app that I was able to get working in a few weeks. Over time the functionality grew.
We recently added in PTO accrual and functionality to debit PTO time. In doing so in a test driven manner was great, as we could put all the edge cases. What we found was that many of the requirements were plentiful with edge cases. For instance, we get paid on the 15th or end of the month, unless that is a weekend. Then we get paid on a Friday – Except if that Friday is a holiday, then the previous Thursday – Except – if that is also a holiday…. So it is really the previous non-weekend, non-holiday on or before the 15th or end of the month. The same holds true to determine the beginning of the billing period. If the Monday is the 2nd, than for some operations the effective billing period start is Tuesday the third…. Ugh…
Our initial thoughts were filled with visions of lots of very similar tests for all contexts that do things depending on the start or end of a billing period. We didn’t want to have lots of duplicate test code to test all edge cases, so we decided to extend the Date object to have a few helper methods to do the complicated logic in one place. We get the full range of the billing period start and end, and then trim off any holidays or weekends. What this did, was allow us to test the complicated logic in unit tests with a full set of complicated edge cases. We created many crazy examples of billing periods starting and ending on weekends, holidays, and holidays before and after weekends. This created a very robust set of methods to be used anywhere in the system.
We then mocked a call to each Date helper method everywhere in the system where it cared about what day it was, and weather it was the start/end of a billing period. We had only a few edge cases now: is it the true effective billing period start/end, or not. Our tests could then focus on the guts of what it actually did, regardless of the effective date.
This demonstrates how powerful unit testing is, and how mocking can really keep your tests concise. It made not only our code cleaner, but our tests cleaner. It reduced duplicate code, and increased our assurance that the code will function as designed.
That being said, it still doesn’t change the fact that implementing HR logic in any language is a pain in the ass. I have worked on a couple of systems for accounting departments in the past, and their business requirements are much worse than HR. Dealing with job codes, general ledger accounts, etc can make your head spin. All I know, is that without TDD, this system would be buggy.
