Chapter 5: Advanced techniques
There's not really such as thing as "advanced TDD", other than practising TDD more diligently, but this chapter lists some situational techniques and things that are outside TDD.
Getting all the various technologies working together in a new project is a big job. Unfamiliar technologies often require experimenting and fiddling. If you don't know how something should be used, it's hard to write a test for it.
The walking skeleton approach can help in this situation. The idea is to start with one end-to-end test against a system which is deployed to production(-like) environment. Then develop just the bare bones of the system, so that it'll contain the main architectural components.
At start the test could just send a "hello world" message which goes through the frontend, backend, database and back again to the frontend. Focus on just getting the end-to-end test passing and putting the architectural components together. Focused unit and integration tests are best added after you have created the architecture, when there are less unknowns.
Then when the end-to-end test passes through the whole architecture, you can start fleshing out the system. As the system grows, keep improving the end-to-end test along with it. Typically it would test the happy path of an important use case which goes through the whole application.
Continuous Integration (CI) is a practice where all team members merge their code changes, many times per day, into the same main branch in version control. Changes to the main branch in turn trigger building the project and running all tests on a shared computer. This helps reduce the risk and magnitude of merge problems, and ensures that the code works on more than the original programmer's machine.
Continuous Integration started as an Extreme Programming (XP) practice in 1997. According to the XP principle of taking what works and turning it to eleven, in 2010 Continuous Delivery (CD) improved on CI by automating the last mile from build to deployment. Some big internet companies deploy to production normally hundreds of times per day. Because each deployment contains only a few new changes, it reduces the risk and magnitude of production failures. Most importantly, it enables faster feedback from real users.
A core tenet of Continuous Delivery is that at a moment's notice, the current development version of the software can be deployed to production, and nobody will even bat an eye. On top of good CI practices, CD requires comprehensive tests on multiple levels so that if all tests pass, you can trust that the software will work in production. Incomplete features must also be designed to be deployable to production, for example by hiding them with feature toggles until they are complete.
Continuous Delivery may include a human decision on when to deploy to production. If that decision is automated and every build which passes its tests is deployed to production automatically, then it's called Continuous Deployment.
Testing in production
When testing before production is topnotch and you practice Continuous Delivery, then it's possible to start testing also in production. This includes getting feedback from how the users are using the application, for example through A/B testing and conversion funnels. Another key term is observability - making the internal states of the system visible.
test && commit || revert (TCR)
TCR is this crazy idea that every time that the tests pass, the code is committed automatically, and if the tests fail, the changes are reverted automatically.
Try it and see what comes out of it. If nothing else, it can be a good exercise.
After you have practiced TDD for over 10 years, and writing tests and testable code is as easy as breathing, there may be times when writing tests after the code is faster.
Testing and clean code need to be ingrained in your nature, so that you have the discipline to always come back to clean up the code and write tests for it. You need to have done your 10 000 hours to know what test-driven good code looks like, how to write testable code, and what tests are needed to test-drive a piece of code. The end result should look indistinguishable from whether it was written test-first or test-last.
Spike and stabilize: Write some experimental code to see if a thing could work. Cutting corners is okay. Test coverage might be lacking. Leave behind TODOs about things that are not of production quality. If the experiment doesn't work, the code can be thrown away. If the code proves useful, then you write the tests for it afterwards and refactor the code up to production quality. Looking at the end result, nobody should be able to tell that the code was not test-driven.
Ginger cake: The story behind the name is about a granny's recipe box. There is a recipe for chocolate cake, listing all the ingredients and instructions. Later in the box there is also a recipe for ginger cake, which reads just "like chocolate cake, but with ginger". As a software development pattern, this can be used when you need to build a new feature which is quite similar to something you've done before - and you know the code intimately. Copy-paste the old code, remove unnecessary parts and customize it suit the new feature.
Proceed to Chapter 6: To infinity and beyond or Exercises