electron/docs/development/testing.md

Testing

We aim to keep the code coverage of Electron high. We ask that all pull request not only pass all existing tests, but ideally also add new tests to cover changed code and new scenarios. Ensuring that we capture as many code paths and use cases of Electron as possible ensures that we all ship apps with fewer bugs.

This repository comes with linting rules for both JavaScript and C++ – as well as unit and integration tests. To learn more about Electron's coding style, please see the coding-style document.

Linting

To ensure that your changes are in compliance with the Electron coding style, run npm run lint, which will run a variety of linting checks against your changes depending on which areas of the code they touch.

Many of these checks are included as precommit hooks, so it's likely your error would be caught at commit time.

Unit Tests

If you are not using build-tools, ensure that the name you have configured for your local build of Electron is one of Testing, Release, Default, or you have set process.env.ELECTRON_OUT_DIR. Without these set, Electron will fail to perform some pre-testing steps.

To run all unit tests, run npm run test. The unit tests are an Electron app (surprise!) that can be found in the spec folder. Note that it has its own package.json and that its dependencies are therefore not defined in the top-level package.json.

To run only specific tests matching a pattern, run npm run test -- -g=PATTERN, replacing the PATTERN with a regex that matches the tests you would like to run. As an example: If you want to run only IPC tests, you would run npm run test -- -g ipc.

Node.js Smoke Tests

If you've made changes that might affect the way Node.js is embedded into Electron, we have a test runner that runs all of the tests from Node.js, using Electron's custom fork of Node.js.

To run all of the Node.js tests:

$ node script/node-spec-runner.js

To run a single Node.js test:

$ node script/node-spec-runner.js parallel/test-crypto-keygen

where the argument passed to the runner is the path to the test in the Node.js source tree.

Testing on Windows 10 devices

Extra steps to run the unit test:

1. Visual Studio 2019 must be installed.

2. Node headers have to be compiled for your configuration.

   ninja -C out\Testing electron:node_headers
   

3. The electron.lib has to be copied as node.lib.

   cd out\Testing
   mkdir gen\node_headers\Release
   copy electron.lib gen\node_headers\Release\node.lib
   

Missing fonts

Some Windows 10 devices do not ship with the Meiryo font installed, which may cause a font fallback test to fail. To install Meiryo:

1. Push the Windows key and search for Manage optional features.
2. Click Add a feature.
3. Select Japanese Supplemental Fonts and click Install.

Pixel measurements

Some tests which rely on precise pixel measurements may not work correctly on devices with Hi-DPI screen settings due to floating point precision errors. To run these tests correctly, make sure the device is set to 100% scaling.

To configure display scaling:

1. Push the Windows key and search for Display settings.
2. Under Scale and layout, make sure that the device is set to 100%.

Multi-Monitor Tests

Some Electron APIs require testing across multiple displays, such as screen detection, window positioning, and display-related events. For contributors working on these features, the virtualDisplay native addon enables you to create and position virtual displays programmatically, making it possible to test multi-monitor scenarios without any physical hardware.

For detailed information on using virtual displays in your tests, see Multi-Monitor Testing.

Platform support: macOS only