Python – What is TDD (Test-Driven Development) ?

What is TDD ?

TDD (Test-driven development) is software design approach where your code is written around your tests.

With TDD the test is first created, this test initially fails. The minimum amount of code is then written to ensure the test passes. This approach provides the following benefits,

  • promotes the creation of more efficient code
  • improves code quality
  • ensures the minimum amount of code is used
  • prevents code regression


Within our example we will use the Python module unittest to show the process of creating a simple class based on TDD.

Write Test

First of we write our test. Our test will pass if our code returns the number 6.

import unittest
from calculator import Calculator

class TestCalculatorCase(unittest.TestCase):
    def setUp(self):
    def test_multiply(self):
        calc = Calculator()
        self.assertTrue(calc.multiply(2, 3) == 6)

if __name__ == '__main__':


Of course when the test is run it fails as we have yet to write any code.

ERROR: test_multiply (__main__.TestCalculatorCase)
Traceback (most recent call last):
 File "<stdin>", line 9, in test_multiply
NameError: global name 'Calculator' is not defined
Ran 1 tests in 0.001s FAILED (errors=1)

Write Code

We then write are code so that it passes based on our test.

class Calculator(object):
    def multiply(self, a, b):
        return a*b

Final Test

We then rerun our test and as we now have the required code it passes.

 Ran 1 test in 0.001s
Rick Donato

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