#Plugins

Harness plugins are the way to extend Harness beyond what it offers out of the box.

Use them to add project-specific capabilities on top of Harness, such as native coverage collection, custom reporting, artifact collection, or workflow-specific automation.

A plugin can react to events such as:

• Harness startup and teardown
• run start and finish
• runtime ready and disconnect events
• Metro initialization and bundle events
• app lifecycle signals
• collection, suite, and test execution events

Each plugin receives a context with useful runtime information such as a logger, project root, current runner, current config, and hook-specific data like the run ID or test file path.

#Defining a Plugin

Use definePlugin() from @react-native-harness/plugins and register the plugin in your Harness config.

import { definePlugin } from '@react-native-harness/plugins';

export const loggingPlugin = () =>
  definePlugin({
    name: 'logging-plugin',
    hooks: {
      harness: {
        beforeCreation: async (ctx) => {
          ctx.logger.info('Harness is starting for', ctx.platform.platformId);
        },
      },
      run: {
        started: async (ctx) => {
          ctx.logger.info('Run started', ctx.runId);
        },
        finished: async (ctx) => {
          ctx.logger.info('Run finished', ctx.runId, ctx.status);
        },
      },
      testFile: {
        finished: async (ctx) => {
          ctx.logger.info('Finished test file', ctx.file, ctx.status);
        },
      },
    },
  });

Then register it in rn-harness.config.mjs:

import {
  applePlatform,
  appleSimulator,
} from '@react-native-harness/platform-apple';
import { loggingPlugin } from './logging-plugin';

export default {
  entryPoint: './src/test.ts',
  appRegistryComponentName: 'App',
  runners: [
    applePlatform({
      name: 'ios',
      device: appleSimulator('iPhone 16 Pro', '18.0'),
      bundleId: 'com.example.app',
    }),
  ],
  plugins: [loggingPlugin()],
};

#Typical Uses

Plugins are a good fit when you want to:

• write custom logs for run start, finish, or failures
• collect screenshots, crash artifacts, or extra diagnostics
• send results to external reporting systems
• trigger project-specific automation around test runs

Keep plugins focused on workflow needs that are specific to your app or team.

#Available Events

The full list of plugin events is defined in the source here:

• packages/plugins/src/types.ts

The public plugin shape is based on nested objects like run.started, runtime.ready, metro.bundleFinished, app.exited, or harness.beforeDispose.