Test classes in PyTest - Build an Automation Script

Verify calculator operations using pytest test class

Preconditions (2)

Step 1: Create a test class named TestCalculator

Step 2: Inside the class, write a setup method to create a Calculator instance

Step 3: Write a test method test_add to verify addition of 2 and 3 equals 5

Step 4: Write a test method test_subtract to verify subtraction of 5 from 10 equals 5

Step 5: Write a test method test_multiply to verify multiplication of 4 and 3 equals 12

Step 6: Write a test method test_divide to verify division of 10 by 2 equals 5

Step 7: Run pytest and observe the test results

✅ Expected Result: All test methods pass confirming Calculator operations work correctly

Automation Requirements - pytest

Assertions Needed:

assert addition result equals expected

assert subtraction result equals expected

assert multiplication result equals expected

assert division result equals expected

Best Practices:

Use test classes to group related tests

Use setup method for common test setup

Use clear and descriptive test method names

Use assert statements for validation

Automated Solution

PyTest

import pytest

class Calculator:
    def add(self, a, b):
        return a + b

    def subtract(self, a, b):
        return a - b

    def multiply(self, a, b):
        return a * b

    def divide(self, a, b):
        if b == 0:
            raise ValueError("Cannot divide by zero")
        return a / b

class TestCalculator:
    def setup_method(self):
        self.calc = Calculator()

    def test_add(self):
        result = self.calc.add(2, 3)
        assert result == 5

    def test_subtract(self):
        result = self.calc.subtract(10, 5)
        assert result == 5

    def test_multiply(self):
        result = self.calc.multiply(4, 3)
        assert result == 12

    def test_divide(self):
        result = self.calc.divide(10, 2)
        assert result == 5

The Calculator class provides basic math operations.

The TestCalculator class groups tests for these operations.

The setup_method runs before each test to create a fresh Calculator instance.

Each test method calls one Calculator method and asserts the result matches the expected value.

This structure keeps tests organized and avoids repeating setup code.

Common Mistakes - 4 Pitfalls

Not using a test class and writing standalone test functions

Not using setup_method and creating Calculator instance inside each test

Using print statements instead of assert for validation

Using unclear test method names like test1, test2

Bonus Challenge

Now add data-driven testing with 3 different input sets for the add method

Show Hint