Branch coverage in PyTest - Framework Patterns

Framework Mode - Branch coverage

Folder Structure

project-root/
├── src/
│   └── calculator.py
├── tests/
│   ├── test_calculator.py
│   ├── __init__.py
│   └── conftest.py
├── pytest.ini
├── requirements.txt
└── README.md
  

Test Framework Layers

• Source Code Layer (src/): Contains the application code to be tested, e.g., calculator.py with functions having branches (if/else).
• Test Layer (tests/): Contains test files like test_calculator.py where pytest test functions verify different branches of the code.
• Fixtures and Setup (conftest.py): Shared test setup or reusable fixtures for tests.
• Configuration (pytest.ini): Configures pytest options including coverage settings.
• Utilities (optional): Helper functions or test data if needed.

Configuration Patterns

Use pytest.ini to configure coverage options for branch coverage:

[pytest]
addopts = --cov=src --cov-branch --cov-report=term-missing
  

This enables branch coverage measurement and shows missing branches in the terminal report.

For environment-specific settings (like test vs. dev), use environment variables or separate config files loaded in conftest.py.

Test Reporting and CI/CD Integration

• Use pytest-cov plugin to generate coverage reports including branch coverage.
• Reports can be output as terminal summary, HTML, XML (for CI tools).
• Integrate with CI/CD pipelines (GitHub Actions, Jenkins, GitLab CI) to run tests and fail builds if branch coverage drops below threshold.
• Example GitHub Actions step to run tests with coverage:

        - name: Run tests with coverage
          run: |
            pytest --cov=src --cov-branch --cov-report=xml
        

Best Practices for Branch Coverage Framework

• Write tests for all decision points: Ensure tests cover both true and false branches of if/else statements.
• Use pytest-cov plugin: It integrates smoothly with pytest and supports branch coverage.
• Keep tests small and focused: Each test should verify one branch or behavior to isolate failures.
• Fail build on coverage drop: Enforce minimum branch coverage thresholds in CI to maintain quality.
• Use clear naming: Name tests to reflect which branch or condition they cover for easy maintenance.

Self Check

Where in this folder structure would you add a new test to verify the false branch of a conditional in the calculator.py file?

Key Result

Organize tests in a dedicated folder with pytest and use pytest-cov to measure branch coverage ensuring all decision branches are tested.

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