This document provides descriptions of Gerrit end-to-end (e2e) test scenarios implemented using the Gatling framework.

Similar scenarios have been successfully used to compare performance of different Gerrit versions or study the Gerrit response under different load profiles. Although mostly for load, scenarios can either be for load or functional (e2e) testing purposes. Functional scenarios may then reuse this framework and Gatling’s usability features such as its protocols (more below) and DSL.

That cross test-scope reusability applies to both Gerrit core scenarios and non-core ones, such as for Gerrit plugins or other potential extensions. End-to-end testing may then include scopes like feature integration, deployment, smoke (and load) testing. These load and functional test scopes should remain orthogonal to the unit and component (aka Gerrit IT-suffixed or acceptance) ones. The term acceptance though may still be coined by organizations to target e2e functional testing.

What is Gatling?

Gatling is mostly a load testing tool which provides out of the box support for the HTTP protocol. Documentation on how to write an HTTP load test can be found here. However, in the scenarios that were initially proposed, the Gatling Git extension was leveraged to run tests at the Git protocol level.

Gatling is written in Scala, but the abstraction provided by the Gatling DSL makes the scenarios implementation easy even without any Scala knowledge. The online End-to-end tests presentation links posted on the homepage have more introductory information.

IDE: IntelliJ

Examples of scenarios can be found in the e2e-tests directory. The files in that directory should be formatted using the mainstream Scala plugin for IntelliJ. The latter is not mandatory but preferred for sbt and Scala IDE purposes in this project. So, Eclipse can also be used alongside as a development IDE; this is described below.


  1. Install the Scala plugin for Eclipse.

  2. Run sbt eclipse from the e2e-tests root directory.

  3. Import the resulting e2e-tests eclipse file inside the Gerrit project, in Eclipse.

  4. You should see errors in Eclipse telling you there are missing packages.

  5. This is due to the sbt-eclipse plugin not properly linking the Gerrit Gatling e2e tests with Gatling Git plugin.

  6. You then have to right-click on the root directory and choose the build path→link source option.

  7. Then you have to browse to .sbt/1.0/staging, find the folder where gatling-git is contained, and choose that.

  8. That last step should link the gatling-git plugin to the project; e2e tests should not show errors anymore.

  9. You may get errors in the gatling-git directory; these should not affect Gerrit Gatling development and can be ignored.

How to build the tests

An sbt-based installation of Scala is required.

The scalaVersion used by sbt once installed is defined in the build.sbt file. That specific version of Scala is automatically used by sbt while building:

sbt compile

The following warning, if present when executing sbt commands, can be removed by creating the related credentials file locally. Dummy values for user and password in that file can be used initially.

[warn] Credentials file ~/.sbt/sonatype_credentials does not exist

The other warning below can be safely ignored, so far. Running the proposed sbt evicted command should only list scala-java8-compat_2.12 as [warn]. The other dependency conflicts should show as [info]. All of the listed conflicts get usually resolved seamlessly or so.

[warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.

Every sbt command can include an optional log level argument. Below, [info] logs are no longer shown:

sbt --warn compile

How to build using Docker

docker build . -t e2e-tests

How to set-up

SSH keys

If you are running SSH commands, the private keys of the users used for testing need to go in /tmp/ssh-keys. The keys need to be generated this way (JSch won’t validate them otherwise):

mkdir /tmp/ssh-keys
ssh-keygen -m PEM -t rsa -C "" -f /tmp/ssh-keys/id_rsa

The public key in /tmp/ssh-keys/ has to be added to the test user(s) SSH Keys in Gerrit. Now, the host from which the latter runs may need public key scanning to become known. This applies to the local user that runs the forthcoming sbt testing commands. An example assuming localhost follows:

ssh-keyscan -t rsa -p 29418 localhost > ~/.ssh/known_hosts

Input file

The CloneUsingBothProtocols scenario is fed with the data coming from the src/test/resources/data/com/google/gerrit/scenarios/CloneUsingBothProtocols.json file. Such a file contains the commands and repository used during the e2e test. That file currently looks like below. This scenario serves as a simple example with no actual load in it. It can be used to test or validate the local setup. More complex scenarios can be further developed, under the package. The uppercase keywords are set through environment properties.

    "url": "ssh://admin@HOSTNAME:SSH_PORT/_PROJECT",
    "cmd": "clone"
    "cmd": "clone"

Valid commands are:

  • clone

  • fetch

  • pull

  • push

Project and HTTP credentials

The example above assumes that the loadtest-repo project exists in the Gerrit under test. The CloneUsingBothProtocols scenario already includes creating that project and deleting it once done with it. That scenario class can be used as an example of how a scenario can compose itself alongside other scenarios (here, CreateProject and DeleteProject).

The HTTP Credentials or password obtained from test user’s Settings (in Gerrit) may be required, in src/test/resources/application.conf, depending on the above commands used. That file’s http section shows which shell environment variables can be used to set those credentials.

Executing the CloneUsingBothProtocols scenario, as is, does require setting the http credentials. That is because of the aforementioned create/delete project (http) scenarios composed within it.

Environment properties

The JAVA_OPTS environment variable can optionally be used to define non-default values for keys found in scenario json data files. That variable can currently be set with either one or many of these supported properties, from the core framework:





Above, the properties can be set with values matching specific deployment topologies under test. The name of the property corresponds to the uppercase keyword found in the json file. For example, hostname above will set the value of HOSTNAME in the aforementioned example.

The example values shown above are the currently coded default ones. For example, the http scheme above could be replaced with https. The framework may support differing or more properties over time.

Replication delay

The replication_delay property allows test scenario steps to wait for that many seconds, prior to expecting a done replication. Its default is 15 seconds and can be set using another value:


There is a short time buffer added to this property. Now, the replication starts after replication plugin’s own replicationDelay, in seconds, and typically takes some more seconds to complete. That whole replication time depends on the system under test. Therefore, this property here should be set to a value high enough, so that the test checks for a done replication at the right time.

Automatic properties

The example keywords also include _PROJECT, prefixed with an underscore, which means that its value gets automatically generated by the scenario. Any property setting for it is therefore not applicable. Its usage differs from the non-prefixed PROJECT keyword, in that sense. Using the latter instead in json files requires setting this JAVA_OPTS property:


Other automatic keys may be used and implemented, always prefixed with an underscore that tells so.

Plugin scenarios

Plugin or otherwise non-core scenarios can also use such properties. The core java package from the example above has to be replaced with the one under which those scenario classes are. Such extending scenarios can also add extension-specific properties. Examples of this can be found in these Gerrit plugins test code:

Power factor

The following core property can be optionally set depending on the runtime environment. The test environments used as reference for scenarios development assume its default value, 1.0. For slower or more complex execution environments, the value can be increased this way for example:


This will make the scenario steps take half more time to expect proper completion. A value smaller than the default, say 0.8, will make scenarios wait somewhat less than how they were developed. Scenario development is often done using locally running Gerrit systems under test, which are sometimes dockerized.

Number of users

The number_of_users property can be used to scale scenario steps to run with the specified number of concurrent users. The value of this property remains 1 by default. For example, this sets the number of concurrent users to 10:


This will make scenarios that support the number_of_users property to inject that many users concurrently for load testing.

How to run tests

Run all tests:

sbt "gatling:test"

Run a single test:

sbt "gatling:testOnly"

Generate the last report:

sbt "gatling:lastReport"

The src/test/resources/logback.xml file configures Gatling’s logging level. To quickly enable detailed logging of http requests and responses, the root level can be set to trace in that file.

How to run using Docker

docker run -it e2e-tests -s

How to run non-core scenarios

Locally adding non-core scenarios, for example from Gerrit plugins, is as simple as copying such files in. Copying is necessary over linking, unless running using Docker (above) is not required. Docker does not support links for files it has to copy over through the Dockerfile (here, the scenario files). Here is how to proceed for adding such external (e.g., plugin) scenario files in:

pushd e2e-tests/src/test/scala
cp -r (or, ln -s) scalaPackageStructure .

pushd e2e-tests/src/test/resources/data
cp -r (or, ln -s) jsonFilesPackageStructure .

The destination folders above readily git-ignore every non-core scenario file added under them. If running using Docker, e2e-tests/Dockerfile may require another COPY line for the hereby added scenarios. Aforementioned sbt or docker commands can then be used to run the added tests.