# 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](
https://source.chromium.org/chromium/chromium/src/+/main: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/ \
```
3. If generating coverage and there are duplicate class files, as can happen
when generating coverage for downstream targets, use the
`--include-substr-filter` option to choose jars in the desired directory. Eg.
for generating coverage report for Clank internal repo
```shell
build/android/generate_jacoco_report.py --format html \
--output-dir /tmp/coverage_report/ --coverage-dir /tmp/coverage/ \
--sources-json-dir out/java_coverage/ \
--include-substr-filter obj/clank
```
