code-coverage

name	code-coverage
description	Use when asked to measure, report, or investigate test code coverage on Windows/MSVC builds - requires OpenCppCoverage and an already-built test binary

Code Coverage

Overview

On Windows/MSVC, line coverage is measured with OpenCppCoverage against an already-built test .exe — it instruments the binary at runtime, no recompilation with special flags needed. This skill does not build anything; the test project must already be compiled (see verify-build skill / memory reference_build.md).

Prerequisites

• OpenCppCoverage.exe installed: winget install OpenCppCoverage (check first with where OpenCppCoverage.exe)
• The relevant *Test.exe already built for the configuration you want (Debug is more accurate than Release — Release inlining/optimization can merge or drop lines, understating coverage)

Process

1. Find the test binary: bin/Debug-windows-x86_64/<Project>Test/<Project>Test.exe
2. Scope --sources to the file(s) under test — without it, OpenCppCoverage instruments the entire binary including gtest/vendor code, which is slow and noisy.
3. Optionally scope --gtest_filter to just the relevant test suite(s), for a faster, focused run.
4. Run:

OpenCppCoverage.exe --sources "Utils\Utils\SSE\Vec3.*" --export_type html:coverage_report -- "bin\Debug-windows-x86_64\UtilsTest\UtilsTest.exe" --gtest_filter="Vec3_*"

(Note the -- before the test binary path — arguments after it are passed straight to the test executable, e.g. --gtest_filter.)

5. Read the results:
   • coverage_report/index.html → aggregate percentage across all matched source files
   • coverage_report/Modules/<TestProject>/<File>.html → per-line coverage for one file (green = covered, red = uncovered)

Common Mistakes

• Omitting --sources — reports coverage for every module loaded (ntdll, gtest, RTTR, ...), burying the file you actually care about.
• Measuring a Release build — optimized-away or merged lines report as covered/uncovered unreliably; prefer Debug.
• Forgetting to rebuild before measuring — OpenCppCoverage reports against whatever the .exe currently contains, not your latest source edits.
• Windows path separators — --sources patterns use backslashes and match against the paths embedded in the PDB, so use Module\Path\File.*, not forward slashes.

Reference

See Tests/readme.md → "Code coverage" section for the canonical project example.