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TDD - Test Driven Development 🛠️

What is TDD?

  • TDD is the process of developing and running automated test before actual development of the application.
  • Relies on the repetition of a very short development cycle.
  • Sometimes called Test First Development
  • The tests drive development

Why do we use TDD?

  • Reduces the number of bugs when applied to legacy projects
  • Decreases bug to code ratio in new projects
  • Increases overall software quality.
  • Increases code quality.
  • TDD is one of the common practices of Agile core development.
  • Agile is feedback driven development and feedback is critical
  • Requirements you start with may change during development cycle

Benefits of using TDD

  • Early bug notification

    • Developers can test their code but in the database world, this often consists of manual tests or one-off scripts.
    • Using TDD, you can build up, over time, a suite of automated tests that you and other developers can rerun.

  • Better Designed, cleaner and more extensible code

    • Helps to understand how the code will be used and how it interacts with other modules.
    • Better design decision, maintainable code.
    • TDD allows writing smaller code having responsibility rather than monolithic procedures with multiple responsibilities.
    • TDD forces to write only production code to pass tests based on user requirements.

  • Confidence to Refactor

    • When refactoring code, there is a greater likelihood of breaks.
    • Having set of automated tests can fix those breaks before release.
    • Proper warning is given when breaks are identified.

Limitations of TDD

  • Large numbers of unit tests can become hard to maintain as the project grows in size.

TDD in Agile

  • Development technique where you must first write a test that fails before you write new functional code.
  • Starts with designing and developing tests for every small functionality and prompts developers to write new code only if an automated test has failed.

Using Pytest

Installing pytest

$ python -m pip install pytest

The test file must include key word test

calc_test

An examples of a simple test:

# content of test_sample.py
def inc(x):
    return x + 1

def test_answer():
    assert inc(3) == 5

To execute it:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 1 item

test_sample.py F                                                     [100%]

================================= FAILURES =================================
_______________________________ test_answer ________________________________

    def test_answer():
>       assert inc(3) == 5
E       assert 4 == 5
E        +  where 4 = inc(3)

test_sample.py:6: AssertionError
========================= short test summary info ==========================
FAILED test_sample.py::test_answer - assert 4 == 5
============================ 1 failed in 0.12s =============================