Code coverage with Jack

Jack supports code coverage with JaCoCo ( During the compilation, it will instrument code using JaCoCo API. Therefore, it requires a dependency to a jacoco-agent.jar that can be imported in the DEX output. Jack supports Jacoco v0.7.5 (see directory external/jacoco in the Android source tree).

Besides, Jack will also produce a coverage metadata file (or description file) in a JSON format. It will be used to generate the report so we can match coverage execution file with source code.

Starting with the Jack Douarn release (4.x), the code coverage is provided with the Jack plugin jack-coverage-plugin.jar.

Enabling code coverage with Jack

Using the Android build system

You can enable code coverage by setting EMMA_INSTRUMENT_STATIC=true in your make command. The build system will compile it with Jack by enabling code coverage and importing the jacoco-agent.jar defined in external/jacoco. It will produce the metadata file in the ‘intermediates’ directory of the app.

For instance, to instrument the Settings app:

EMMA_INSTRUMENT_STATIC=true mmma -j32 packages/apps/Settings

The medatafile is located in $ANDROID_BUILD_TOP/out/target/common/obj/APPS/Settings_intermediates/coverage.em

Once the application is instrumented, you can install it and execute it to produce code coverage execution file.

You can define class name filters to select which classes will be instrumented (all classes are instrumented by default) by defining the following build variables:

  • LOCAL_JACK_COVERAGE_INCLUDE_FILTER: a comma-separated list of class names to include
  • LOCAL_JACK_COVERAGE_EXCLUDE_FILTER: a comma-separated list of class names to exclude These filters will be passed on the Jack command-line (see below) only when code coverage is enabled.

Using Jack command-line

To enable code coverage with Jack command-line, pass the following command-line options:

--pluginpath <code_coverage_plugin_jar>
-D jack.coverage=true
-D jack.coverage.metadata.file=<coverage_metadata_file_path>
-D jack.coverage.jacoco.package=<jacoco_internal_package_name>


  • <code_coverage_plugin_jar> is the path to the plugin jar file. In the Android tree, it is located in the prebuilts/sdk/tools directory.
  • <coverage_metadata_file_path> is a mandatory property that indicates the path of the file that will contain coverage information. This file must be passed to reporting tool to generate the report (see section Generating the report below)
  • <jacoco_internal_package_name> is an optional property that indicates the fully qualified name of the internal package name containing the class ‘Offline’ in the associated jacoco-agent.jar file. This package name is different for each release of JaCoCo library. If this property is not provided, Jack will automatically look for a Jacoco package which starts with org.jacoco.agent.rt.internal.

Note: because Jack's code coverage support is based on Jacoco, it is mandatory that Jacoco classes are available at compilation time. They can be either on the classpath (--classpath) or imported as a static library in the output (--import).

Jack also supports optional include and exclude class filtering based on class name:

-D jack.coverage.jacoco.include=<includes>
-D jack.coverage.jacoco.exclude=<excludes>


  • <includes> is a comma-separated list of fully-qualified class names to include
  • <excludes> is a comma-separated list of fully-qualified class names to exclude

Wildcards characters ‘?’ and ‘*’ are accepted to replace respectively one character or multiple characters.

You can find the full command-line usage with

java -jar <jack_jar> --help

You can also find the description of all properties (including those for code coverage) with

java -jar <jack_jar> --pluginpath <code_coverage_plugin_jar> --plugin --help-properties

Collecting code coverage

To produce coverage execution data, instrumented classes must be executed and coverage data be dumped in a coverage execution file. For Android instrumentation tests, the frameworks can do so automatically:

adb shell am instrument -w -e coverage true <package_name>/<instrumentation_class_name>

For the case of the Settings app tests:

adb shell am instrument -w -e coverage true

Once the tests are finished, the location of the coverage execution file should be printed in the console.

Generating the report

A coverage report can be generated using the jack-jacoco-reporter.jar file. This is a command-line tool taking at least three inputs:

  • the coverage metadata file(s) produced by Jack
  • the coverage execution file(s) produced during execution
  • an existing directory where the report is generated

It is also recommended to indicate the directories containing the source code of classes being analyzed to link coverage information with the source code.

The command then looks like:

java -jar jack-jacoco-reporter.jar --metadata-file <metadata_file> --coverage-file <execution_file> --report-dir <report_directory> --source-dir <source_dir_1> ... --source-dir <source_dir_N>

You can find the full command-line usage with

java -jar jack-jacoco-reporter.jar --help