Import Cobalt 21.master.0.301702
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+# Android code coverage instructions
+
+These are instructions for collecting code coverage data for android
+instrumentation and JUnit tests.
+
+[TOC]
+
+## How JaCoCo coverage works
+
+In order to use JaCoCo code coverage, we need to create build time pre-instrumented
+class files and runtime **.exec** files. Then we need to process them using the
+**build/android/generate_jacoco_report.py** script.
+
+## How to collect coverage data
+
+1. Use the following GN build arguments:
+
+ ```gn
+ target_os = "android"
+ use_jacoco_coverage = true
+ ```
+
+ Now when building, pre-instrumented files will be created in the build directory.
+
+2. Run tests, with option `--coverage-dir <directory>`, to specify where to save
+ the .exec file. For example, you can run chrome JUnit tests:
+ `out/Debug/bin/run_chrome_junit_tests --coverage-dir /tmp/coverage`.
+
+3. The coverage results of JUnit and instrumentation tests will be merged
+ automatically if they are in the same directory.
+
+## How to generate coverage report
+
+1. Now we have generated .exec files already. We can create a JaCoCo HTML/XML/CSV
+ report using `generate_jacoco_report.py`, for example:
+
+ ```shell
+ build/android/generate_jacoco_report.py \
+ --format html \
+ --output-dir /tmp/coverage_report/ \
+ --coverage-dir /tmp/coverage/ \
+ --sources-json-dir out/Debug/ \
+ ```
+ Then an index.html containing coverage info will be created in output directory:
+
+ ```
+ [INFO] Loading execution data file /tmp/coverage/testTitle.exec.
+ [INFO] Loading execution data file /tmp/coverage/testSelected.exec.
+ [INFO] Loading execution data file /tmp/coverage/testClickToSelect.exec.
+ [INFO] Loading execution data file /tmp/coverage/testClickToClose.exec.
+ [INFO] Loading execution data file /tmp/coverage/testThumbnail.exec.
+ [INFO] Analyzing 58 classes.
+ ```
+
+2. For XML and CSV reports, we need to specify `--output-file` instead of `--output-dir` since
+ only one file will be generated as XML or CSV report.
+ ```shell
+ build/android/generate_jacoco_report.py \
+ --format xml \
+ --output-file /tmp/coverage_report/report.xml \
+ --coverage-dir /tmp/coverage/ \
+ --sources-json-dir out/Debug/ \
+ ```
+
+ or
+
+ ```shell
+ build/android/generate_jacoco_report.py \
+ --format csv \
+ --output-file /tmp/coverage_report/report.csv \
+ --coverage-dir /tmp/coverage/ \
+ --sources-json-dir out/Debug/ \
+ ```
