Calculate test coverage for the new code only. Usable in pull/merge requests.

calculate_new_coverage.py

"""
Calculates test coverage for the new code only, that is for the added and
changed lines of code.

Usage:

pytest --cov --cov-report=xml
git diff master..HEAD |python calculate_new_coverage.py --coverage-report coverage.xml
"""

import sys
import xml.etree.ElementTree as ET
import argparse


def parse_diff(diff_lines):
    changes = {}
    current_file = ""
    line_num = 0

    for line in diff_lines:
        if line.startswith('+++ b/'):
            current_file = line[6:].strip()
            if not current_file.endswith('.py'):
                current_file = None
        elif line.startswith('@@'):
            line_num = int(line.split(" ")[2].split(",")[0][1:]) + 1
        elif line.startswith('+') and current_file:
            changes.setdefault(current_file, []).append(line_num)
            line_num += 1
        elif line.startswith(' ') and current_file:
            line_num += 1
    return changes


def calculate_new_coverage(diff_changes, coverage_report_path):
    tree = ET.parse(coverage_report_path)
    root = tree.getroot()
    total_lines, covered_lines = 0, 0

    for file_path in diff_changes.keys():
        for file in root.findall(".//class[@filename='%s']" % file_path):
            for line in file.findall('.//line'):
                line_num = int(line.get('number'))
                if line_num in diff_changes[file_path]:
                    total_lines += 1
                    if int(line.get('hits')) > 0:
                        covered_lines += 1

    if total_lines == 0:
        return 100

    return (covered_lines / total_lines) * 100


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument(
        '--coverage-report', required=True, help="Path to pytest coverage XML report"
    )
    args = parser.parse_args()

    diff_changes = parse_diff(sys.stdin)
    new_coverage = calculate_new_coverage(diff_changes, args.coverage_report)

    print(f"{int(new_coverage)}%")