Code Coverage

Code coverage can be checked using Clang's source-based coverage tools. You must use the GN argument use_clang_coverage=true. It is recommended to do this in a separate output directory since the added instrumentation will affect performance and generate profile data every time a binary is run. You can read more about Clang coverage in the Clang documentation.

Viewing Coverage Reports Online

Individual CL Coverage (Trybots)

When you upload a change to Gerrit and run CQ tryjobs:

  • The linux_x64 trybot instruments the files modified by your CL and runs openscreen_unittests and e2e_tests.
  • In the Gerrit review UI, line coverage changes are highlighted directly in the diff viewer.
  • On the LUCI build page for try/linux_x64, click the html report link (under the calculate code coverage step or in the build overview) to open an interactive HTML report showing coverage for files touched by the CL.

Entire Repository Coverage (CI Builder)

When changes land on main:

  • The ci/linux_x64 postsubmit builder instruments all source files in the repository and runs openscreen_unittests and e2e_tests.
  • On the LUCI build page for ci/linux_x64, an html report link is provided under the calculate code coverage step.
  • The full repository coverage HTML report can be viewed directly in your browser at:
    https://storage.cloud.google.com/code-coverage-data/postsubmit/chromium.googlesource.com/openscreen/<commit_hash>/ci/linux_x64/<build_id>/html_report/index.html

Analyzing Coverage Locally

Option 1: Build, Run, and Generate Locally

To measure and inspect full repository coverage entirely on your local workstation:

  1. Configure and build with coverage enabled:

    gn gen out/coverage --args="use_clang_coverage=true is_debug=false"
ninja -C out/coverage openscreen_unittests

  2. Run tests with LLVM_PROFILE_FILE set to produce raw profile data:

    LLVM_PROFILE_FILE="default.profraw" out/coverage/openscreen_unittests

  3. Merge the raw profile data into an indexed .profdata file:

    third_party/llvm-build/Release+Asserts/bin/llvm-profdata merge \
    -sparse default.profraw -o coverage.profdata

  4. Generate the HTML report:

    third_party/llvm-build/Release+Asserts/bin/llvm-cov show \
    out/coverage/openscreen_unittests \
    -instr-profile=coverage.profdata \
    -format=html \
    -output-dir=out/coverage_html \
    [filter paths]

    Note: [filter paths] is an optional list of subdirectories or source files (e.g., cast/ or cast/streaming/) to restrict the report scope. If omitted, all repository sources are included.

  5. View the report: Open out/coverage_html/index.html in your browser.

Option 2: Generate Locally from CI Profile Data

If you want to view or query coverage for a specific landed commit without running all unit tests locally, you can download the merged .profdata produced by the CI builder:

  1. Build the binary locally at the target commit:

    gn gen out/coverage --args="use_clang_coverage=true is_debug=false"
ninja -C out/coverage openscreen_unittests

  2. Locate the build details on the LUCI ci/linux_x64 console to get the <commit_hash> and <build_id>.

  1. Download the merged profile data:

    gsutil cp \
    gs://code-coverage-data/postsubmit/chromium.googlesource.com/openscreen/<commit_hash>/ci/linux_x64/<build_id>/merged.profdata \
    .

  2. Generate the HTML report using your local binary and the downloaded profile data:

    third_party/llvm-build/Release+Asserts/bin/llvm-cov show \
    out/coverage/openscreen_unittests \
    -instr-profile=merged.profdata \
    -format=html \
    -output-dir=out/coverage_html \
    [filter paths]

  3. View the report: Open out/coverage_html/index.html in your browser.

Coverage for Fuzzers

The same process can be used to check the coverage of a fuzzer's corpus. Just add -runs=0 to the fuzzer arguments to ensure it only runs the existing corpus and exits:

LLVM_PROFILE_FILE="fuzzer.profraw" out/coverage/<fuzzer_name> -runs=0