First PyTest test - Build an Automation Script

Verify addition function returns correct sum

Preconditions (2)

Step 1: Create a Python file named test_math.py

Step 2: Define a function add(a, b) that returns the sum of a and b

Step 3: Write a test function test_add() that calls add(2, 3)

Step 4: Assert that the result of add(2, 3) is 5

Step 5: Run pytest on the test_math.py file

✅ Expected Result: Pytest runs the test and shows that test_add passed successfully

Automation Requirements - pytest

Assertions Needed:

Assert that add(2, 3) == 5

Best Practices:

Use clear function names starting with test_

Keep test functions simple and focused

Use assert statements for validation

Name test files starting with test_

Automated Solution

PyTest

def add(a, b):
    return a + b

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

The add function simply returns the sum of two numbers.

The test function test_add calls add(2, 3) and stores the result.

Then it uses assert to check if the result equals 5.

Pytest automatically finds functions starting with test_ and runs them.

This simple test confirms the addition works as expected.

Common Mistakes - 3 Pitfalls

{'mistake': "Not prefixing test function with 'test_'", 'why_bad': 'Pytest will not recognize or run the function as a test', 'correct_approach': "Always start test function names with 'test_' so pytest can find them"}

Using print statements instead of assert

Not running pytest from the correct directory

Bonus Challenge

Now add data-driven testing with 3 different pairs of numbers and their expected sums

Show Hint

Practice

1. What does PyTest look for to identify a test function?

easy

A. Functions decorated with @pytest.test

B. Functions ending with _test

C. Functions starting with test_

D. Functions containing assert keyword

Solution

1. Step 1: Understand PyTest naming convention

   PyTest automatically finds functions whose names start with test_.

2. Step 2: Compare options with PyTest rules

   Only functions starting with test_ are recognized as tests by default.

3. Final Answer:

   Functions starting with test_ -> Option C

4. Quick Check:

   PyTest test function = starts with test_ [OK]

Hint: Look for functions starting with test_ to find tests [OK]

Common Mistakes:

• Thinking functions ending with _test are tests
• Believing assert keyword alone marks a test
• Assuming decorators are needed for basic tests

2. Which of the following is the correct syntax for a simple PyTest test function?

easy

A. def add_test():\n assert 1 + 1 == 2

B. def test_add():\n assert 1 + 1 == 2

C. def test_add():\n assert 1 + 1 == 3

D. def testAdd():\n assert 1 + 1 == 2

Solution

1. Step 1: Check function name format

   PyTest requires test functions to start with test_, so test_add is correct.

2. Step 2: Verify assertion correctness

   The assertion 1 + 1 == 2 is true, so the test will pass.

3. Final Answer:

   def test_add():\n assert 1 + 1 == 2 -> Option B

4. Quick Check:

   Correct test name and true assert = def test_add():\n assert 1 + 1 == 2 [OK]

Hint: Use def test_...() with assert for valid PyTest tests [OK]

Common Mistakes:

• Naming function without test_ prefix
• Using incorrect assertion values
• Using camelCase instead of snake_case for test names

3. What will be the result when running this PyTest test?

def test_example():
    x = 5
    y = 2
    assert x - y == 3

medium

A. Test passes successfully

B. SyntaxError occurs

C. Test fails with AssertionError

D. Test is skipped automatically

Solution

1. Step 1: Evaluate the assertion expression

   Calculate x - y which is 5 - 2 = 3.

2. Step 2: Compare with asserted value

   The assertion checks if 3 == 3, which is true, so no error is raised.

3. Final Answer:

   Test passes successfully -> Option A

4. Quick Check:

   5 - 2 equals 3 means assert passes [OK]

Hint: Calculate assert expression; true means test passes [OK]

Common Mistakes:

• Assuming test fails without checking assertion
• Confusing syntax errors with assertion failures
• Thinking tests skip without skip decorators

4. Identify the error in this PyTest test function:

def test_sum():
    total = 2 + 2
    assert total = 4

medium

A. Using single equals (=) instead of double equals (==) in assert

B. Function name does not start with test_

C. Missing return statement in test function

D. Indentation error in function body

Solution

1. Step 1: Check the assert statement syntax

   The assert uses = which is assignment, not comparison. It should be ==.

2. Step 2: Confirm function name and indentation

   The function name starts with test_ and indentation is correct, so no error there.

3. Final Answer:

   Using single equals (=) instead of double equals (==) in assert -> Option A

4. Quick Check:

   Assert needs ==, not = [OK]

Hint: Use == in assert, not = for comparison [OK]

Common Mistakes:

• Using = instead of == in assert
• Thinking return is needed in test functions
• Confusing indentation errors with syntax errors

5. You want to test a function multiply(a, b) that returns the product of two numbers. Which PyTest test function correctly tests that multiply(3, 4) returns 12?

hard

A. def test_multiply():\n assert multiply(3, 4) == 7

B. def test_multiply():\n assert multiply(3, 4) = 12

C. def multiply_test():\n assert multiply(3, 4) == 12

D. def test_multiply():\n assert multiply(3, 4) == 12

Solution

1. Step 1: Verify test function name

   The function name must start with test_, so test_multiply is correct.

2. Step 2: Check assertion correctness

   The assertion must compare with == and the expected result is 12, so assert multiply(3, 4) == 12 is correct.

3. Final Answer:

   def test_multiply():\n assert multiply(3, 4) == 12 -> Option D

4. Quick Check:

   Correct name and assert with == 12 = def test_multiply():\n assert multiply(3, 4) == 12 [OK]

Hint: Test functions start with test_ and assert expected == actual [OK]

Common Mistakes:

• Wrong expected value in assert
• Wrong function name prefix
• Using = instead of == in assert