How to Write Good Tests?

The banner image shows a picture of a bridge called 南桥 (Nan Qiao, literally means the South Bridge.) This bridge is located at Dujiangyan, which is a small city 50km away from Chengdu, Sichuan, China. Since I had my high-school in Dujiangyan, I have a lot of precious memories there. I miss the people, inexpensive but delicious food, the way of living, and the memory when I rode a bike to travel between Chengdu and Dujiangyan with my best friends (around 100 km in total.)

Recently I am reading a book called The Art of Readable Code by Dustin Boswell. This is a textbook for a code-review class that I am taking. I think it is a good idea to share about some contents with you so that 1) I can deepen my understanding, 2) You can learn something from here!

¶Chapter 14: Testing and Readability

KEY IDEA: Test code should be readable so that other coders are comfortable changing or adding tests.

1. Test should be more readable

   • When writing a test, we should hide less important details.

2. Minimize the test statement

   • We should make the input/ expectation of a test clear so that it is very easy to add more tests.

3. Helper function

   • By extract some unimportant logics into a separate function, we can focus on the main implementation of the test itself.

4. Make error message readable

   • Utilize better assert in the language assertEqual in python, for example.

   • Create custom error message like:

CheckScoresBeforeAfter() failed,
Input: "-5, 1, 4, -99998.7, 3"
Expected Output: "4, 3, 1"
Actual Output: "1, 3, 4"

5. Choose good input

In general, you should pick the simplest set of inputs that completely exercise the code.

6. Simplifying the Input Values

   • The simple test that achieves the purpose is the best!

7. Multiple tests

   • multiple tests for multiple purposes with clear input/expectation

8. Naming

   • Name the test as the description.

   • Test__<FunctionName>_<Situation>()

void Test_SortAndFilterDocs_BasicSorting() {
...
}

• For helper function, we can name it differently as “test-unware”.

If you write your code knowing you’ll be writing a test for it later, a funny thing happens: you start designing your code so that it’s easy to test! Fortunately, coding this way also means that you create better code in general. Test-friendly designs often lead naturally to wellorganized code, with separate parts to do separate things.

​ I hope this helps, but I strongly recommend you to read this book because it contains a lot of examples of good/bad practices. It is concise and very helpful for me and you who want to be a professional programmer!

2022/1/21

¶Some add-on

Programs have to be written with two goals in mind:

• Communicating with computer
• Communicating with people

¶Three themes:

1. Safe from bugs:

• Correctness
• Defensiveness: correctness in future

2. Easy to understand:
   • communicate with future programmers
   • good design helps future you/maintainers
3. Ready to change

¶Software Engineering is not Hacking

Engineers are pessimists, so:

1. write a little bit at a time, testing as you go.
2. document the assumptions that code depends on
3. defend code against carelessness.

¶Git Commit Message

We can use a concise and helpful commit message format such as :

<type>: <Message>
feat: blablabla