Selenium

Automates browsers. That's it!

Contributing • Installing • Building • Developing • Testing • Documenting • Releasing

Selenium is an umbrella project encapsulating a variety of tools and libraries enabling web browser automation. Selenium specifically provides an infrastructure for the W3C WebDriver specification — a platform and language-neutral coding interface compatible with all major web browsers.

The project is made possible by volunteer contributors who've generously donated thousands of hours in code development and upkeep.

This README is for developers interested in contributing to the project. For people looking to get started using Selenium, please check out our User Manual for detailed examples and descriptions, and if you get stuck, there are several ways to Get Help.

Contributing

Please read CONTRIBUTING.md before submitting your pull requests.

Installing

These are the requirements to create your own local dev environment to contribute to Selenium.

All Platforms

• Bazelisk, a Bazel wrapper that automatically downloads the version of Bazel specified in .bazelversion file and transparently passes through all command-line arguments to the real Bazel binary.
• Java JDK version 17 or greater (e.g., Java 17 Temurin)
  • Set JAVA_HOME environment variable to location of Java executable (the JDK not the JRE)
  • To test this, try running the command javac. This command won't exist if you only have the JRE installed. If you're met with a list of command-line options, you're referencing the JDK properly.

MacOS

• Xcode including the command-line tools. Install the latest version using: xcode-select --install
• Rosetta for Apple Silicon Macs. Add build --host_platform=//:rosetta to the .bazelrc.local file. We are working to make sure this isn't required in the long run.

Windows

Several years ago Jim Evans published a great article on Setting Up a Windows Development Environment for the Selenium .NET Language Bindings; This article is out of date, but it includes more detailed descriptions and screenshots that some people might find useful.

Alternative Dev Environments

If you want to contribute to the project, but do not want to set up your own local dev environment, there are two alternatives available.

Using GitPod

Rather than creating your own local dev environment, GitPod provides a ready to use environment for you.

Using Dev Container

As an alternative you can build a Dev Container - basically a docker container - suitable for building and testing Selenium using the devcontainer.json in the .devcontainer directory. Supporting IDEs like VS Code or IntelliJ IDEA should point you to how such a container can be created.

Using Docker Image

You can also build a Docker image suitable for building and testing Selenium using the Dockerfile in the dev image directory.

Using Worktrees

Bazel keeps its build outputs and downloaded dependencies under each checkout by default, which means working from multiple worktrees re-downloads dependencies and rebuilds artifacts. Pointing Bazel at user-level caches avoids that.

Add the following to /path/to/your/home/.bazelrc

common --disk_cache=/path/to/your/home/.cache/bazel-disk
common --repository_cache=/path/to/your/home/.cache/bazel-repo

--disk_cache stores compiled action outputs; --repository_cache stores downloaded external dependencies (e.g. http_archive tarballs). Both directories grow unbounded over time — prune them periodically if disk space matters. Keep the cache on the same filesystem as your checkouts so Bazel can hardlink instead of copy.

Bazel also creates a separate output base (compiled outputs, analysis cache, and the Bazel server) per checkout path. Unlike the caches above, it is not removed when you delete a worktree — so frequently created and discarded worktrees leak gigabytes of stale output.

On macOS/Linux, make a worktree self-cleaning by pointing its output base inside the worktree. Add this to that worktree's .bazelrc.local:

startup --output_base=.local/output-base

.local/ is gitignored and excluded in .bazelignore, so removing the worktree removes its output base with it. The shared --disk_cache/--repository_cache above still keep downloads and action outputs shared across worktrees.

(Windows users should instead keep startup --output_user_root=C:/tmp in .bazelrc.windows.local as described above, to avoid path-length limits — do not nest the output base deeper inside the repo on Windows.)

Building

Selenium is built using a common build tool called Bazel, to allow us to easily manage dependency downloads, generate required binaries, build and release packages, and execute tests; all in a fast, efficient manner. For a more detailed discussion, read Simon Stewart's article on Building Selenium

Often we wrap Bazel commands with our custom Rake wrapper. These are run with the ./go command.

The common Bazel commands are:

• bazel build — evaluates dependencies, compiles source files and generates output files for the specified target. It's used to create executable binaries, libraries, or other artifacts.
• bazel run — builds the target and then executes it. It's typically used for targets that produce executable binaries.
• bazel test — builds and runs the target in a context with additional testing functionality
• bazel query — identifies available targets for the provided path.

Each module that can be built is defined in a BUILD.bazel file. To execute the module you refer to it starting with a //, then include the relative path to the file that defines it, then :, then the name of the target. For example, the target to build the Grid is named executable-grid and it is defined in the 'selenium/java/src/org/openqa/selenium/grid/BAZEL.build' file. So to build the grid you would run: bazel build //java/src/org/openqa/selenium/grid:executable-grid.

The Bazel documentation has a handy guide for various shortcuts and all the ways to build multiple targets, which Selenium makes frequent use of.

To build everything for a given language:

bazel build //<language>/...

To build just the grid there is an alias name to use (the log will show where the output jar is located):

bazel build grid

To make things more simple, building each of the bindings is available with this ./go command:

./go <language>:build

Developing

Java

IntelliJ

Most of the team uses Intellij for their day-to-day editing. If you're working in IntelliJ, then we highly recommend installing the Bazel IJ plugin which is documented on its own site.

To use Selenium with the IntelliJ Bazel plugin, import the repository as a Bazel project, and select the project view file from the scripts directory. ij.bazelproject for Mac/Linux and ij-win.bazelproject for Windows.

Linting

We also use Google Java Format for linting, so using the Google Java Formatter Plugin is useful; there are a few steps to get it working, so read their configuration documentation. There is also an auto-formatting script that can be run: ./scripts/format.sh

Local Installation

While Selenium is not built with Maven, you can build and install the Selenium pieces for Maven to use locally by deploying to your local maven repository (~/.m2/repository), using:

./go java:install

Updating Dependencies

Dependencies are defined in the file MODULE.bazel.

To update a dependency, modify the version in the MODULE.bazel file and run:

RULES_JVM_EXTERNAL_REPIN=1 bazel run @maven//:pin

To automatically update and pin new dependencies, run:

./go java:update

Python

Linting and Formatting

We follow the PEP8 Style Guide for Python Code (except we use a 120 character line length). This is checked and enforced with ruff, a linting/formatting tool. There is also an auto-formatting script that can be run: ./scripts/format.sh

Local Installation

To run Python code locally without building/installing the package, you must first install the dependencies:

pip install -r py/requirements_lock.txt

Then, build the generated files and copy them into your local source tree:

./go py:local_dev

After that, you can import the selenium package directly from source from the py directory.

Instead of running from source, you can build and install the selenium package (wheel) locally:

./go py:install

This will attempt to install into the global Python site-packages directory, which might not be writable. To avoid this, you should create and activate a virtual environment before installing.

Ruby

Instead of using irb, you can create an interactive REPL with all gems loaded using: bazel run //rb:console

If you want to debug code, you can do it via debug gem:

1. Add binding.break to the code where you want the debugger to start.
2. Run tests with ruby_debug configuration: bazel test --config ruby_debug .
3. When debugger starts, run the following in a separate terminal to connect to debugger:

bazel-selenium/external/bundle/bin/rdbg -A

If you want to use RubyMine for development, you can configure it use Bazel artifacts:

1. Open rb/ as a main project directory.
2. From the selenium (parent) directory, run ./go rb:local_dev to create up-to-date artifacts.
3. In Settings / Languages & Frameworks / Ruby SDK and Gems add new Interpreter pointing to ../bazel-selenium/external/rules_ruby++ruby+ruby/dist/bin/ruby.
4. You should now be able to run and debug any spec. It uses Chrome by default, but you can alter it using environment variables specified in Ruby Testing section below.

Rust

Rust Bazel dependencies are generated directly from rust/Cargo.toml and rust/Cargo.lock.

Testing

There are a number of bazel configurations specific for testing.

Common Options Examples

Here are examples of arguments we make use of in testing the Selenium code:

• --pin_browsers=false - use Selenium Manager to locate browsers/drivers
• --manager=host - compile Selenium Manager from source instead of downloading the pinned binary
• --headless - run browsers in headless mode (supported be Chrome, Edge and Firefox)
• --flaky_test_attempts 3 - re-run failed tests up to 3 times
• --local_test_jobs 1 - control parallelism of tests
• --cache_test_results=no, -t- - disable caching of test results and re-runs all of them
• --test_output all - print all output from the tests, not just errors
• --test_output streamed - run all tests one by one and print its output immediately
• --test_env FOO=bar - pass extra environment variable to test process
• --run_under="xvfb-run -a" - prefix to insert before the execution

Filtering

Selenium tests can be filtered by size:

• small — typically unit tests where no browser is opened
• large — typically tests that actually drive a browser
• medium — tests that are more involved than simple unit tests, but not fully driving a browser

These can be filtered using the test_size_filters argument like this:

bazel test //<language>/... --test_size_filters=small

Tests can also be filtered by tag like:

bazel test //<language>/... --test_tag_filters=this,-not-this

If there are multiple --test_tag_filters, only the last one is considered, so be careful if also using an inherited config

Language specific testing guides can be found in a TESTING.md file in the applicable directory.

Linux

bazel test --test_env=DISPLAY=:99 //java/... --test_tag_filters=chrome

bazel test --run_under="xvfb-run -a" //java/...

Documenting

API documentation can be found here:

• C#
• JavaScript
• Java
• Python
• Ruby

To update API documentation for a specific language: ./go :docs

To update all documentation: ./go all:docs

Releasing

The full process for doing a release can be found in the wiki

Releasing is a combination of building and publishing, which often requires coordination of multiple executions and additional processing. As discussed in the Building section, we use Rake tasks with the ./go command for these things. These ./go commands include the --stamp argument to provide necessary information about the constructed asset.

You can build and release everything with:

./go all:release

To build and release a specific language:

./go <language>:release

If you have access to the Selenium EngFlow repository, you can have the assets built remotely and downloaded locally using:

./go all:release['--config', 'release']