https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/Recent content in Code coverage for black-box tests, in any language on tomato blogHugoen-USWed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/go/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/go/Build with -cover, point GOCOVERDIR at a directory, and go tool covdata reads what ran. No agent, nothing in the code.https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/rust/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/rust/Build with LLVM’s source-based coverage, set LLVM_PROFILE_FILE, and read the profile with the toolchain’s own llvm-profdata and llvm-cov.https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/jvm/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/jvm/Nothing to rebuild: the JaCoCo agent instruments classes as they load and writes its data from a shutdown hook, which the JVM runs on SIGTERM by itself.https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/python/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/python/coverage.py’s startup hook measures any Python process that sees COVERAGE_PROCESS_START, so the command in tomato.yml stays exactly as it is.https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/nodejs/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/nodejs/Coverage is built into Node: set NODE_V8_COVERAGE and V8 writes what ran when the process exits. c8 turns it into reports. Just make sure the process does exit.https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/other-languages/Wed, 21 Oct 2026 03:00:00 +0200https://tomatool.github.io/blog/posts/code-coverage-for-black-box-tests/other-languages/The same shape works wherever the runtime can write coverage when the process ends: .NET, Ruby, PHP and C/C++, with what is different about each.