Single parameter in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest single parameter test

What is the output of this pytest test when run?

PyTest

import pytest

@pytest.mark.parametrize('num', [1, 2, 3])
def test_is_positive(num):
    assert num > 0

if __name__ == '__main__':
    pytest.main(['-v'])

A SyntaxError during test collection

B 1 test passed, 2 failed

C 3 tests passed

D All tests skipped

💡 Hint

Each parameter value runs the test once.

The test runs three times with num=1, 2, and 3. All are positive, so all pass.

❓ assertion

intermediate

Assertion failure with single parameter

Given this test, which input causes the assertion to fail?

PyTest

import pytest

@pytest.mark.parametrize('value', [1, 2, -1])
def test_positive(value):
    assert value > 0

A value = 1

B value = -1

C value = 0

D All values pass

💡 Hint

Check which values are not greater than zero.

Only -1 is less than or equal to zero, so the assertion fails for value = -1.

❓ locator

advanced

Best locator for pytest parameter name

Which locator correctly identifies the parameter name in this pytest decorator?

PyTest

@pytest.mark.parametrize('input_value', [10, 20])
def test_func(input_value):
    assert input_value > 0

A JSON path for parameter list

B XPath locating function name 'test_func'

C CSS selector for function body

D Regex matching 'parametrize\('([^']+)'

💡 Hint

The parameter name is inside the string in parametrize decorator.

The parameter name is the string inside the parametrize decorator. Regex can extract it reliably.

🔧 Debug

advanced

Debugging failing pytest parameter test

Why does this pytest test fail?

PyTest

import pytest

@pytest.mark.parametrize('x', [1, 2, 3])
def test_double(x):
    assert x * 2 == '2', 'Expected double to be string "2"'

A Comparing int to str causes assertion failure

B SyntaxError in parametrize decorator

C TypeError because x is not iterable

D Test passes without error

💡 Hint

Check the types compared in the assertion.

The test compares an integer (x*2) to a string '2', causing assertion failure but no TypeError.

❓ framework

expert

Effect of single parameter on test count in pytest

If a pytest test uses @pytest.mark.parametrize with a single parameter having 4 values, how many test cases are executed?

PyTest

import pytest

@pytest.mark.parametrize('val', [10, 20, 30, 40])
def test_val(val):
    assert val > 0

A 4 test cases executed

B 1 test case executed

C 16 test cases executed

D 0 test cases executed

💡 Hint

Each parameter value runs the test once.

Each value in the parameter list runs the test once, so 4 values mean 4 test cases.

Practice

1. What is the purpose of using a single parameter in a pytest test function?

easy

A. To define multiple test functions at once

B. To make the test function run only once

C. To skip the test function during execution

D. To pass different values to the test function for repeated testing

Solution

1. Step 1: Understand pytest parameterization

   Pytest allows passing parameters to test functions to run the same test with different inputs.

2. Step 2: Role of a single parameter

   A single parameter lets you supply multiple values to the test, so it runs multiple times with each value.

3. Final Answer:

   To pass different values to the test function for repeated testing -> Option D

4. Quick Check:

   Single parameter = multiple test runs [OK]

Hint: Single parameter means testing with different inputs [OK]

Common Mistakes:

• Thinking single parameter defines multiple tests
• Confusing parameter with skipping tests
• Assuming single parameter runs test once only

2. Which of the following is the correct syntax to use a single parameter with pytest's @pytest.mark.parametrize decorator?

easy

A. @pytest.mark.parametrize('num', 1, 2, 3)

B. @pytest.mark.parametrize(num, [1, 2, 3])

C. @pytest.mark.parametrize('num', [1, 2, 3])

D. @pytest.mark.parametrize(['num'], 1, 2, 3)

Solution

1. Step 1: Check parameter name format

   The parameter name must be a string inside quotes, e.g., 'num'.

2. Step 2: Check values format

   The values must be inside a list or iterable, e.g., [1, 2, 3].

3. Final Answer:

   @pytest.mark.parametrize('num', [1, 2, 3]) -> Option C

4. Quick Check:

   Parametrize syntax = string + list [OK]

Hint: Parameter name in quotes, values in list brackets [OK]

Common Mistakes:

• Not quoting the parameter name
• Passing values without list brackets
• Using wrong argument structure

3. What will be the output when running this pytest code?

import pytest

@pytest.mark.parametrize('x', [2, 4])
def test_double(x):
    assert x * 2 == 4

medium

A. First test passes, second test fails

B. Both tests fail

C. First test fails, second test passes

D. Both tests pass

Solution

1. Step 1: Evaluate first test with x=2

   2 * 2 = 4, assertion is true, test passes.

2. Step 2: Evaluate second test with x=4

   4 * 2 = 8, assertion 8 == 4 is false, test fails.

3. Final Answer:

   First test passes, second test fails -> Option A

4. Quick Check:

   2*2=4 pass, 4*2=8 fail [OK]

Hint: Check each input separately for assertion [OK]

Common Mistakes:

• Assuming all tests pass without checking values
• Mixing up which input causes failure
• Ignoring assertion logic

4. Identify the error in this pytest code using a single parameter:

import pytest

@pytest.mark.parametrize('val', 1, 2, 3)
def test_positive(val):
    assert val > 0

medium

A. Parameter name should not be in quotes

B. Missing list brackets around parameter values

C. Test function must have two parameters

D. Assertion should use == instead of >

Solution

1. Step 1: Check parametrize values format

   Values must be inside a list or iterable, e.g., [1, 2, 3].

2. Step 2: Identify missing brackets

   Code passes values as separate arguments instead of a single list, causing syntax error.

3. Final Answer:

   Missing list brackets around parameter values -> Option B

4. Quick Check:

   Values need list brackets [OK]

Hint: Values must be in a list or tuple [OK]

Common Mistakes:

• Passing values without brackets
• Removing quotes from parameter name
• Wrong assertion operator

5. Given this test function, how can you modify it to test multiple string inputs using a single parameter?

def test_is_uppercase(s):
    assert s.isupper()

hard

A. Add @pytest.mark.parametrize('s', ['HELLO', 'WORLD']) above the function

B. Change function to accept two parameters s and t

C. Use a for loop inside the test to iterate over strings

D. Call test_is_uppercase multiple times manually

Solution

1. Step 1: Understand parameterizing tests

   Using @pytest.mark.parametrize allows running the test multiple times with different inputs.

2. Step 2: Apply parametrize decorator with string list

   Adding @pytest.mark.parametrize('s', ['HELLO', 'WORLD']) runs test_is_uppercase twice with each string.

3. Final Answer:

   Add @pytest.mark.parametrize('s', ['HELLO', 'WORLD']) above the function -> Option A

4. Quick Check:

   Parametrize decorator runs test with multiple inputs [OK]

Hint: Use @pytest.mark.parametrize with list of inputs [OK]

Common Mistakes:

• Trying to pass multiple parameters instead of one
• Using loops inside test instead of parametrize
• Calling test manually instead of using pytest features