Architecture Patterns with Python

Chapter 5. TDD in High Gear and Low Gear

We’ve introduced the service layer to capture some of the additional orchestration responsibilities we need from a working application. The service layer helps us clearly define our use cases and the workflow for each: what we need to get from our repositories, what pre-checks and current state validation we should do, and what we save at the end.

But currently, many of our unit tests operate at a lower level, acting directly on the model. In this chapter we’ll discuss the trade-offs involved in moving those tests up to the service-layer level, and some more general testing guidelines.

Harry Says: Seeing a Test Pyramid in Action Was a Light-Bulb Moment

Here are a few words from Harry directly:

I was initially skeptical of all Bob’s architectural patterns, but seeing an actual test pyramid made me a convert.

Once you implement domain modeling and the service layer, you really actually can get to a stage where unit tests outnumber integration and end-to-end tests by an order of magnitude. Having worked in places where the E2E test build would take hours (“wait ‘til tomorrow,” essentially), I can’t tell you what a difference it makes to be able to run all your tests in minutes or seconds.

Read on for some guidelines on how to decide what kinds of tests to write and at which level. The high gear versus low gear way of thinking really changed my testing life.

How Is Our Test Pyramid Looking?

Let’s see what this move to using a service layer, ...