Multiple parameters in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest with multiple parameters

What will be the output when running this pytest code with multiple parameters?

PyTest

import pytest

@pytest.mark.parametrize("x", [1, 2])
@pytest.mark.parametrize("y", [3, 4])
def test_sum(x, y):
    assert x + y > 3

A 4 tests run, all pass

B 2 tests run, all pass

C 2 tests run, some fail

D 4 tests run, some fail

💡 Hint

Remember how pytest combines multiple parametrize decorators.

pytest runs the test for all combinations of parameters from multiple @pytest.mark.parametrize decorators, so 2 values for x and 2 for y produce 4 tests. All pass because all sums are greater than 3.

❓ assertion

intermediate

Correct assertion for multiple parameters

Which assertion correctly verifies that the product of parameters a and b is always even in this test?

PyTest

import pytest

@pytest.mark.parametrize("a", [1, 2])
@pytest.mark.parametrize("b", [2, 3])
def test_product_even(a, b):
    # Choose the correct assertion below

A assert (a - b) % 2 == 0

B assert (a + b) % 2 == 0

C assert (a * b) % 2 == 1

D assert (a * b) % 2 == 0

💡 Hint

Check which operation and condition ensures even product.

The product is even if divisible by 2, so (a * b) % 2 == 0 is the correct assertion. Other options check sum or difference or odd product.

🔧 Debug

advanced

Identify the error in multiple parameter test

What error will this pytest code raise when run?

PyTest

import pytest

@pytest.mark.parametrize("x, y", [(1, 2), (3, 4)])
@pytest.mark.parametrize("z", [5, 6])
def test_values(x, y, z):
    assert x + y + z > 0

A pytest runs 4 tests, all pass

B TypeError: test_values() missing 1 required positional argument: 'z'

C pytest runs 6 tests, all pass

D ValueError: too many values to unpack

💡 Hint

Check how pytest combines multiple parametrize decorators with multiple arguments.

pytest combines parameters by Cartesian product. The first parametrize provides 2 tuples (x,y), second provides 2 values for z, so 2*2=4 tests. But since x,y are grouped, and z separate, total tests are 4. All sums are positive, so all pass.

❓ locator

advanced

Best locator for multiple parameter test cases

In a test report, which locator best identifies a test case with parameters x=2 and y=3 in pytest?

A test_sum(x=2,y=3)

B test_sum[2-3]

C test_sum_2_3

D test_sum(2,3)

💡 Hint

pytest uses a specific format for parameterized test IDs.

pytest shows parameterized test IDs in the format test_name[param1-param2], so test_sum[2-3] is the correct locator. Others are not standard pytest locators.

❓ framework

expert

Understanding parameter combination in pytest

Given these decorators, how many total test cases will pytest generate?

PyTest

import pytest

@pytest.mark.parametrize("a", [1, 2])
@pytest.mark.parametrize("b, c", [(3, 4), (5, 6)])
@pytest.mark.parametrize("d", [7])
def test_func(a, b, c, d):
    pass

A 8 tests

B 2 tests

C 4 tests

D 16 tests

💡 Hint

Multiply the number of values in each parametrize considering grouping.

pytest combines parameters by Cartesian product. a has 2 values, (b,c) has 2 tuples, d has 1 value. Total tests = 2 * 2 * 1 = 4 tests. But pytest applies parametrize decorators bottom-up, so the total is 2 (a) * 2 (b,c) * 1 (d) = 4 tests.

Practice

1. What is the main purpose of using @pytest.mark.parametrize with multiple parameters in pytest?

easy

A. To run the same test function with different sets of input values

B. To skip tests conditionally based on input values

C. To group multiple test functions into one

D. To generate test reports automatically

Solution

1. Step 1: Understand the role of @pytest.mark.parametrize

   This decorator allows running a test multiple times with different inputs.

2. Step 2: Recognize the benefit of multiple parameters

   Using multiple parameters lets you test combinations of inputs easily in one test function.

3. Final Answer:

   To run the same test function with different sets of input values -> Option A

4. Quick Check:

   Multiple parameters = multiple input sets [OK]

Hint: Parametrize runs tests repeatedly with different inputs [OK]

Common Mistakes:

• Thinking it skips tests instead of running multiple times
• Confusing it with grouping tests
• Assuming it generates reports automatically

2. Which of the following is the correct syntax to parametrize a test function with two parameters a and b in pytest?

easy

A. @pytest.mark.parametrize((a, b), [(1, 2), (3, 4)])

B. @pytest.mark.parametrize('a, b', [(1, 2), (3, 4)])

C. @pytest.mark.parametrize([a, b], [(1, 2), (3, 4)])

D. @pytest.mark.parametrize('a b', [(1, 2), (3, 4)])

Solution

1. Step 1: Recall the correct parameter names format

   Pytest expects a string with parameter names separated by commas, e.g., 'a, b'.

2. Step 2: Check the value list format

   Values must be a list of tuples matching the parameters, e.g., [(1, 2), (3, 4)].

3. Final Answer:

   @pytest.mark.parametrize('a, b', [(1, 2), (3, 4)]) -> Option B

4. Quick Check:

   Parameter names as string with commas [OK]

Hint: Use a string with comma-separated names for parameters [OK]

Common Mistakes:

• Using tuple or list instead of string for parameter names
• Missing commas between parameter names
• Using space instead of comma to separate names

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

import pytest

@pytest.mark.parametrize('x, y', [(1, 2), (3, 4)])
def test_sum(x, y):
    assert x + y == 3

medium

A. First test passes, second test fails

B. Both tests fail

C. Both tests pass

D. First test fails, second test passes

Solution

1. Step 1: Evaluate first test with inputs (1, 2)

   Sum is 1 + 2 = 3, assertion 3 == 3 passes.

2. Step 2: Evaluate second test with inputs (3, 4)

   Sum is 3 + 4 = 7, assertion 7 == 3 fails.

3. Final Answer:

   First test passes, second test fails -> Option A

4. Quick Check:

   Check sums against 3 [OK]

Hint: Calculate sums for each tuple and compare [OK]

Common Mistakes:

• Assuming all tests pass without checking values
• Ignoring that assertion compares to fixed number 3
• Confusing which test input causes failure

4. Identify the error in this pytest code using multiple parameters:

import pytest

@pytest.mark.parametrize('a, b', [1, 2, 3])
def test_multiply(a, b):
    assert a * b > 0

medium

A. The test function must return a value

B. The parameter names should be a list, not a string

C. The assertion syntax is incorrect

D. The parameter values should be tuples, not integers

Solution

1. Step 1: Check the parameter values format

   Values must be a list of tuples matching parameters (a, b), but here it's a list of integers.

2. Step 2: Understand why this causes error

   Pytest tries to unpack each integer into two variables, causing a TypeError.

3. Final Answer:

   The parameter values should be tuples, not integers -> Option D

4. Quick Check:

   Values must match parameter count [OK]

Hint: Use tuples for multiple parameters values [OK]

Common Mistakes:

• Passing a flat list instead of list of tuples
• Thinking parameter names must be a list
• Expecting test function to return a value

5. You want to test a function is_even_sum(a, b) that returns True if the sum of a and b is even. Which @pytest.mark.parametrize setup with a single decorator correctly tests all combinations of a from [1, 2] and b from [3, 4] respectively?

hard

A. @pytest.mark.parametrize('a', [1, 2])
@pytest.mark.parametrize('b', [3, 4])

B. @pytest.mark.parametrize('a, b', [(1, 2), (3, 4)])

C. @pytest.mark.parametrize('a, b', [(1, 3), (1, 4), (2, 3), (2, 4)])

D. @pytest.mark.parametrize('a, b', [(1, 3), (2, 4)])

Solution

1. Step 1: Understand the need to test all combinations

   We want to test every pair from a=[1,2] and b=[3,4], so all 4 pairs must be covered.

2. Step 2: Recognize the benefit of multiple parameters

   @pytest.mark.parametrize('a, b', [(1, 3), (1, 4), (2, 3), (2, 4)]) lists all pairs explicitly: (1,3), (1,4), (2,3), (2,4).

3. Final Answer:

   @pytest.mark.parametrize('a, b', [(1, 3), (1, 4), (2, 3), (2, 4)]) -> Option C

4. Quick Check:

   All pairs listed explicitly [OK]

Hint: List all pairs explicitly for full coverage [OK]

Common Mistakes:

• Missing some pairs in the list
• Using separate decorators without knowing cartesian product effect
• Confusing parameter order or values