Branch coverage in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Branch coverage with simple if-else

What is the output of the following pytest test when run with branch coverage enabled?

PyTest

def check_number(x):
    if x > 0:
        return "Positive"
    else:
        return "Non-positive"

def test_check_number():
    assert check_number(5) == "Positive"
    assert check_number(-1) == "Non-positive"

A Test passes but branch coverage is 50%

B Test passes and branch coverage is 100%

C Test fails due to assertion error

D Test passes but branch coverage is 0%

💡 Hint

Branch coverage means each branch of if-else is executed at least once.

Both branches of the if-else are tested: x=5 covers the 'if' branch, x=-1 covers the 'else' branch. So branch coverage is 100%.

❓ assertion

intermediate

Assertion to ensure full branch coverage

Which assertion in pytest ensures that both branches of this function are tested for full branch coverage?

PyTest

def is_even(n):
    if n % 2 == 0:
        return True
    else:
        return False

A assert is_even(2) and not is_even(3)

B assert is_even(2) == True

C assert is_even(3) == False

D assert is_even(0) == True

💡 Hint

To cover both branches, test both even and odd numbers.

Option A tests is_even with 2 (even) and 3 (odd), covering both branches. Other options test only one branch.

🔧 Debug

advanced

Identify missing branch coverage in test

Given this function and test, which branch is NOT covered?

PyTest

def classify_age(age):
    if age < 18:
        return "Minor"
    elif age < 65:
        return "Adult"
    else:
        return "Senior"

def test_classify_age():
    assert classify_age(10) == "Minor"
    assert classify_age(30) == "Adult"

A The 'Minor' branch is not covered

B The 'Adult' branch is not covered

C The 'Senior' branch is not covered

D All branches are covered

💡 Hint

Check which return statements are executed by the test inputs.

Test inputs cover 'Minor' and 'Adult' branches but never test age >= 65, so 'Senior' branch is not covered.

❓ framework

advanced

Using pytest-cov for branch coverage

Which pytest command correctly runs tests with branch coverage reporting?

A pytest --cov=my_module --cov-branch

B pytest --cov=my_module --branch

C pytest --coverage=my_module --branch

D pytest --cov-branch my_module

💡 Hint

The option for branch coverage is '--cov-branch' with pytest-cov.

Option A uses correct syntax: '--cov' to specify module and '--cov-branch' to enable branch coverage.

🧠 Conceptual

expert

Understanding branch coverage impact

Why is branch coverage considered a stronger metric than statement coverage in testing?

A Because branch coverage only counts executed lines, ignoring conditions

B Because branch coverage measures performance of the code during tests

C Because statement coverage requires testing all input values, branch coverage does not

D Because branch coverage ensures every possible path decision is tested, not just each line

💡 Hint

Think about what branch coverage tracks compared to statement coverage.

Branch coverage requires testing both true and false outcomes of each decision, ensuring more thorough testing than statement coverage which only checks if lines run.

Practice

1.

What does branch coverage measure in pytest testing?

easy

A. It checks if all decision paths in the code are tested.

B. It measures how many lines of code are executed.

C. It counts the number of test cases written.

D. It verifies the syntax correctness of the test code.

Solution

1. Step 1: Understand branch coverage concept

   Branch coverage ensures every possible path in decision points (like if-else) is tested.

2. Step 2: Compare with other coverage types

   Line coverage counts executed lines, but branch coverage focuses on decision paths.

3. Final Answer:

   It checks if all decision paths in the code are tested. -> Option A

4. Quick Check:

   Branch coverage = all decision paths tested [OK]

Hint: Branch coverage tests all if-else paths, not just lines [OK]

Common Mistakes:

• Confusing branch coverage with line coverage
• Thinking it counts test cases
• Assuming it checks syntax errors

2.

Which pytest command option enables branch coverage measurement?

easy

A. pytest --cov --cov-branch

B. pytest --branch-coverage

C. pytest --cov-branch

D. pytest --coverage-branch

Solution

1. Step 1: Recall pytest coverage options

   The option --cov enables coverage measurement, and --cov-branch adds branch coverage.

2. Step 2: Identify correct combined command

   Both options must be used together as pytest --cov --cov-branch to measure branch coverage.

3. Final Answer:

   pytest --cov --cov-branch -> Option A

4. Quick Check:

   Use --cov with --cov-branch for branch coverage [OK]

Hint: Use both --cov and --cov-branch together [OK]

Common Mistakes:

• Using only --cov-branch without --cov
• Typing incorrect option names
• Assuming branch coverage is default

3.

Given this code snippet tested with pytest and branch coverage enabled, what is the branch coverage result?

def check_num(x):
    if x > 0:
        return "Positive"
    else:
        return "Non-positive"

# Test cases:
assert check_num(5) == "Positive"

medium

A. 100% branch coverage

B. 75% branch coverage

C. 0% branch coverage

D. 50% branch coverage

Solution

1. Step 1: Identify branches in the code

   The function has two branches: one for x > 0 and one for else (x ≤ 0).

2. Step 2: Check which branches are tested

   The test calls check_num(5), which covers only the x > 0 branch, missing the else branch.

3. Final Answer:

   50% branch coverage -> Option D

4. Quick Check:

   One branch tested out of two = 50% [OK]

Hint: Test all if-else paths to get 100% branch coverage [OK]

Common Mistakes:

• Assuming one test covers all branches
• Confusing line coverage with branch coverage
• Ignoring else branch testing

4.

Identify the error in this pytest test that aims for full branch coverage:

def classify(n):
    if n > 10:
        return "High"
    elif n > 5:
        return "Medium"
    else:
        return "Low"

def test_classify():
    assert classify(12) == "High"
    assert classify(7) == "Medium"

medium

A. Syntax error in the test function.

B. Incorrect expected values in assertions.

C. Missing test for the else branch (n ≤ 5).

D. The function classify has no return statement.

Solution

1. Step 1: Analyze branches in classify()

   There are three branches: n > 10, n > 5, and else (n ≤ 5).

2. Step 2: Check test coverage of branches

   Tests cover n=12 (High) and n=7 (Medium), but no test covers n ≤ 5 (Low) branch.

3. Final Answer:

   Missing test for the else branch (n ≤ 5). -> Option C

4. Quick Check:

   All branches need tests for full coverage [OK]

Hint: Test all if, elif, else branches to avoid missing coverage [OK]

Common Mistakes:

• Assuming two tests cover all branches
• Looking for syntax errors where none exist
• Ignoring else branch testing

5.

You have this function. Which set of test inputs achieves 100% branch coverage?

def analyze_score(score):
    if score >= 90:
        return "A"
    elif score >= 75:
        return "B"
    else:
        return "C"

hard

A. [90, 85, 76]

B. [95, 80, 70]

C. [91, 74, 60]

D. [89, 84, 73]

Solution

1. Step 1: Identify all branches

   Branches: score ≥ 90 ("A"), score ≥ 75 ("B"), else "C".

2. Step 2: Check which inputs cover all branches

   Input 95 covers "A" branch; 80 covers score ≥ 75 ("B"); 70 covers else "C" branch. This covers all branches.

3. Final Answer:

   [95, 80, 70] -> Option B

4. Quick Check:

   Test inputs cover all if-elif-else paths [OK]

Hint: Pick inputs hitting each if, elif, else branch [OK]

Common Mistakes:

• Missing coverage for one of the branches
• Choosing inputs that skip else branch
• Assuming close values cover all branches