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Introduction to Test-Driven Development

Test Driven Development in a Nutshell

Test Driven Development is a practice that developers use to build high quality programs and prevent errors from developing in their programs. Before a single line of code gets written, developers write tests first. The number one reason this is an important practice is because tests minimize the amount of errors and bugs in the code. It seems counterintuitive to write tests first, but there are a few reasons why developers work this way:

1. Design TDD forces you to think about the design of your code before you write it. It's easy to jump right into implementing the features of your application, but stopping to think about how exactly you want your code to function makes for well-designed and thoughtful programs.

2. Discipline If you don't write tests first, you might never get around to writing them period. It might feel like a chore to write tests first, but you'll be glad at the end of the day that you have a full suite of tests to keep your code running smoothly and bug-free.

3. Less Work By repeating the process of 1: write test, 2: write code to make the test pass, where developers write one test then write the actual code to run the test on, developers end up writing only the code they need. It's an arduous process, so superfluous code comes with a lot of baggage (more tests!). Thus, developers ultimately only write the code that's wholly necessary.

How It Works

The typical test development cycle can be summed up with "red, green, refactor." Red: write a test and run it. It fails because you haven't written the actual program code to make it work! Green: Write your code, and make the test pass. Refactor: look at the code and see if you can make it any better.

1. Write a test to describe a small feature you want to build. When you run the test, it'll fail. (That's the red part.)
2. Write just enough code to make the test pass. Now when you run the test, it should pass. (This is the green part.)
3. Refactor your code. Make that code as succinct, clear, and DRY as possible. Refactor as necessary and retest.
4. Rinse and repeat!

Pytest - A Python Testing Framework

Tests are written using a program called Pytest (among others), and the tests are usually stored in scripts starting with test_, such as test_data_retrieval.py.

Failures are good. Let me repeat: failures are good. They are part of step 1 in the TDD process, and they are breadcrumbs on the path to success. Read the failures carefully, change your code, and run pytest again until everything is passing.

Summary

In this lesson, we learned about Test-Driven Development, and how we can use the Red-Green-Refactor pattern to write code in a safe, industry-standard way.