16-Testing-with-Python

Testing

Done to test whether block of code is running well or throwing errors

Why Test?

• Reduce bugs in code
• Ensures that your bugs stay fixed
• Ensure new features don't break old ones

Writing tests can slow you down. It's not necessary to have them for all your projects - big or small. It's more up to personal preference.

It's a good idea to write them you have a large scale project with customers. clients, multiple developers, etc. depending and working on it.

Test Driven Development (TDD)

• Tests are written first
• Then write code to make those tests pass
• Once tests pass, the feature is complete
• Just one of the way to write tests, you can change the order as per your preference

"Red, Green, Refactor" Way

It's a just mantra that people follow while doing TDD

1. Red - Write a test that fails
2. Green - Write the minimal amount of code to pass test
3. Refactor - Clean up code, while ensuring tests still pass

Assertions

• assert keyword accepts an expression to check if it's true
• Raises an AssertionError if expression is falsy
• Returns None if expression is truthy
• Accepts option error msg as second argument

def add_positive_nums(x,y):
  assert x > 0 and y > 0, "Both the numbers must be positive"
  return x+y

print(add_positive_nums(2, 5)) # 7
add_positive_nums(3, -5) # AssertionError: Both the numbers must be positive

If a Python file is run with the -O flag assertions will not be evaluated.

Therefore don't make your code dependent on assertions as they can be ignored.

doctests

• allows us to write tests inside doc strings
• we have to write code in a certain way like inside of a REPL
• if we write tests this way, it can also work as a documentation for other devs along with being a test
• there's a special command to run the doctests w/o having to evaluate anything

python -m doctest -v file_name.py

This will show all the tests that ran, expected output, actual output, no. of passed and failed tests.

• We have to be really careful while mentioning expected output inside doctests. Things like quotation marks, empty spaces, list (or dict) order, etc. can really be a pain at times.

Unit Tests

Unit testing is a technique where we test small individual components (units) as we go

unittest

• Module used for this that comes with a lot of built in assertions
• Unit tests can be written as classes that inherit from unittest.TestCase
• This gives us a lot of assertions
• Tests are run by calling unittest.main()

There are a bunch of different assertions method provided by the module. We can refer to the documentation for more info about them.

setUp & tearDown

• setUp - A function used to run something before every test
• tearDown - A function used to run something after every test
• Names are really imp and should be the same