Conditional parametrize in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is parametrize in pytest?

Parametrize allows you to run the same test function with different input values, making tests efficient and organized.

intermediate

How can you conditionally parametrize tests in pytest?

You can use Python code or fixtures to decide which parameters to pass, so tests run only with relevant data.

intermediate

Example of using @pytest.mark.parametrize with a condition inside the test function.

You parametrize all data but skip or assert only for certain conditions inside the test using if statements.

beginner

Why use conditional parametrize instead of multiple test functions?

It keeps tests DRY (Don't Repeat Yourself), easier to maintain, and runs only needed cases based on conditions.

intermediate

What is a simple way to skip certain parameter sets in pytest based on a condition?

Use pytest.param with marks=pytest.mark.skipif(condition, reason='...') inside @pytest.mark.parametrize.

What does @pytest.mark.parametrize do?

A Generates test reports

B Skips a test unconditionally

C Runs tests in parallel

D Runs a test multiple times with different inputs

Parametrize runs the same test function with different sets of input values.

How can you skip a parameter set conditionally in pytest?

A Use <code>pytest.param(..., marks=pytest.mark.skipif(condition))</code>

B Use <code>pytest.skip()</code> inside the test

C Use <code>assert False</code> in the test

D Remove the parameter from the list

Using pytest.param with skipif mark skips that parameter set based on the condition.

Why is conditional parametrize useful?

A To run tests only with relevant inputs based on conditions

B To avoid writing tests

C To make tests slower

D To run all tests regardless of input

Conditional parametrize helps run tests only for inputs that matter in the current context.

Which Python feature helps decide parameters dynamically in pytest?

A List comprehension

B Global variables only

C If statements and functions

D No Python code can be used

You can use if statements and functions to build parameter lists conditionally.

What happens if a test is skipped using skipif in parametrize?

A Test fails

B Test is ignored and marked skipped

C Test runs normally

D Test crashes

Tests marked with skipif are ignored and shown as skipped in reports.

Explain how to use conditional parametrize in pytest with an example.

Think about skipping some inputs based on a condition.

Why is conditional parametrize better than writing multiple test functions for different inputs?

Consider the DRY principle.

Practice

1. What is the main purpose of using pytest.param with skipif inside @pytest.mark.parametrize?

easy

A. To mark tests as expected failures

B. To run all test cases regardless of conditions

C. To conditionally skip specific test cases based on environment or conditions

D. To parametrize tests without any conditions

Solution

1. Step 1: Understand pytest.param with skipif

   This syntax allows marking individual parameters to be skipped if a condition is true.

2. Step 2: Purpose of conditional skipping

   This helps run only relevant tests in certain environments, skipping others automatically.

3. Final Answer:

   To conditionally skip specific test cases based on environment or conditions -> Option C

4. Quick Check:

   Conditional skipping = skipif with pytest.param [OK]

Hint: Use pytest.param with skipif to skip tests conditionally [OK]

Common Mistakes:

• Thinking skipif skips all tests, not just specific params
• Confusing skipif with xfail
• Not using pytest.param inside parametrize

2. Which of the following is the correct syntax to skip a parameter when Python version is less than 3.8 using pytest.mark.parametrize?

easy

A. @pytest.mark.parametrize('x', [pytest.param(1, marks=pytest.mark.skipif(sys.version_info < (3,8), reason='Old Python'))])

B. @pytest.mark.parametrize('x', [pytest.param(1, skipif=sys.version_info < (3,8))])

C. @pytest.mark.parametrize('x', [pytest.param(1, marks=skipif(sys.version_info < (3,8)))])

D. @pytest.mark.parametrize('x', [pytest.param(1, marks=pytest.skipif(sys.version_info < (3,8)))])

Solution

1. Step 1: Identify correct usage of skipif mark

   The skipif mark must be used inside pytest.mark.skipif with a reason string.

2. Step 2: Check syntax correctness

   @pytest.mark.parametrize('x', [pytest.param(1, marks=pytest.mark.skipif(sys.version_info < (3,8), reason='Old Python'))]) correctly uses pytest.mark.skipif with condition and reason inside marks parameter.

3. Final Answer:

   @pytest.mark.parametrize('x', [pytest.param(1, marks=pytest.mark.skipif(sys.version_info < (3,8), reason='Old Python'))]) -> Option A

4. Quick Check:

   Use pytest.mark.skipif with marks and reason [OK]

Hint: Use marks=pytest.mark.skipif(condition, reason='') inside pytest.param [OK]

Common Mistakes:

• Using skipif without pytest.mark
• Omitting the reason argument
• Passing skipif as a direct argument instead of marks

3. Given the code below, what will be the output when running pytest on Python 3.7?

import sys
import pytest

@pytest.mark.parametrize('num', [
    pytest.param(1, marks=pytest.mark.skipif(sys.version_info < (3,8), reason='Skip on old Python')),
    2,
    3
])
def test_numbers(num):
    assert num > 0

medium

A. All three tests run and pass

B. Test with num=1 is skipped; tests with num=2 and num=3 run and pass

C. All tests are skipped

D. Test with num=1 fails due to skipif syntax error

Solution

1. Step 1: Analyze skipif condition with Python 3.7

   sys.version_info < (3,8) is True for Python 3.7, so param with num=1 is skipped.

2. Step 2: Check other parameters

   Parameters 2 and 3 have no skip marks, so their tests run and pass the assertion.

3. Final Answer:

   Test with num=1 is skipped; tests with num=2 and num=3 run and pass -> Option B

4. Quick Check:

   skipif True skips param; others run [OK]

Hint: Check skipif condition against environment to predict skipped tests [OK]

Common Mistakes:

• Assuming all tests run regardless of skipif
• Confusing skipif with xfail
• Thinking skipif causes syntax error

4. Identify the error in the following code snippet that uses conditional parametrize:

import pytest

@pytest.mark.parametrize('val', [
    pytest.param(10, marks=pytest.mark.skipif('sys.version_info < (3,8)', reason='Old Python')),
    20
])
def test_val(val):
    assert val > 0

medium

A. The skipif condition is a string instead of a boolean expression

B. Missing import of sys module

C. pytest.param cannot be used inside parametrize

D. The reason argument is missing in skipif

Solution

1. Step 1: Check skipif condition type

   The condition is passed as a string, but skipif expects a boolean expression, not a string.

2. Step 2: Confirm other parts

   sys module is not imported, but the main error is the string condition. pytest.param usage and reason argument are correct.

3. Final Answer:

   The skipif condition is a string instead of a boolean expression -> Option A

4. Quick Check:

   skipif condition must be boolean, not string [OK]

Hint: skipif condition must be a boolean expression, not a string [OK]

Common Mistakes:

• Passing condition as string instead of boolean
• Ignoring missing sys import (not main error here)
• Misusing pytest.param outside parametrize

5. You want to run a test with parameters mode set to 'fast', 'slow', and 'medium'. However, you want to skip the 'slow' mode test only if an environment variable SKIP_SLOW is set to '1'. Which is the correct way to write this conditional parametrize in pytest?

hard

A. import os
@pytest.mark.parametrize('mode', [
'fast',
pytest.param('slow', marks=pytest.mark.skipif('os.getenv("SKIP_SLOW") == "1"')),
'medium'
])

B. import os
@pytest.mark.parametrize('mode', [
'fast',
pytest.param('slow', skipif=os.getenv('SKIP_SLOW') == '1'),
'medium'
])

C. import os
@pytest.mark.parametrize('mode', [
'fast',
pytest.param('slow', marks=pytest.skipif(os.getenv('SKIP_SLOW') == '1')),
'medium'
])

D. import os
@pytest.mark.parametrize('mode', [
'fast',
pytest.param('slow', marks=pytest.mark.skipif(os.getenv('SKIP_SLOW') == '1', reason='Skip slow mode')),
'medium'
])

Solution

1. Step 1: Use os.getenv to check environment variable

   os.getenv('SKIP_SLOW') returns the value of the environment variable as a string.

2. Step 2: Apply skipif mark correctly

   Use pytest.mark.skipif with a boolean condition and a reason inside marks parameter of pytest.param.

3. Step 3: Verify syntax correctness

   import os @pytest.mark.parametrize('mode', [ 'fast', pytest.param('slow', marks=pytest.mark.skipif(os.getenv('SKIP_SLOW') == '1', reason='Skip slow mode')), 'medium' ]) correctly uses marks=pytest.mark.skipif(condition, reason='...') and imports os.

4. Final Answer:

   import os @pytest.mark.parametrize('mode', [ 'fast', pytest.param('slow', marks=pytest.mark.skipif(os.getenv('SKIP_SLOW') == '1', reason='Skip slow mode')), 'medium' ]) -> Option D

5. Quick Check:

   Use marks=pytest.mark.skipif with env check and reason [OK]

Hint: Use os.getenv and marks=pytest.mark.skipif with reason to skip params [OK]

Common Mistakes:

• Passing skipif as direct argument instead of marks
• Using string condition instead of boolean
• Omitting reason in skipif mark