Android code coverage instructions

These are instructions for collecting code coverage data for android instrumentation and junit tests.

How EMMA coverage works

In order to use EMMA code coverage, we need to create build time .em files and runtime .ec files. Then we need to process them using the build/android/generate_emma_html.py script.

How to collect EMMA coverage data

1. Use the following GN build arguments:

    target_os = "android"
    emma_coverage = true
    emma_filter = "org.chromium.chrome.browser.ntp.*,-*Test*,-*Fake*,-*Mock*"

The filter syntax is as documented for the EMMA coverage filters.

Now when building, .em files will be created in the build directory.

2. Run tests, with option --coverage-dir <directory>, to specify where to save the .ec file. For example, you can run chrome junit tests: out/Debug/bin/run_chrome_junit_tests --coverage-dir /tmp/coverage.

3. Turn off strict mode when running instrumentation tests by adding --strict-mode=off because the EMMA code causes strict mode violations by accessing disk.

4. Use a pre-L Android OS (running Dalvik) because code coverage is not supported in ART.

5. The coverage results of junit and instrumentation tests will be merged automatically if they are in the same directory.

6. Now we have both .em and .ec files. We can create a html report using generate_emma_html.py, for example:

   build/android/generate_emma_html.py \
       --coverage-dir /tmp/coverage/ \
       --metadata-dir out/Debug/ \
       --output example.html

Then an example.html containing coverage info will be created:

   EMMA: writing [html] report to [<your_current_directory>/example.html] ...