playwright-performance-reporter

Collect performance metrics from the browser dev tools during playwright test execution

Index

• Install
• Usage
  • Setup Reporter
  • Chromium
    • Setup Browser
• Advanced Configurations
  • Sampling
  • Custom Metric Observer
  • Presenters
    • How Presenters Work
    • Using Predefined Presenters
    • Custom Presenters
• Output

Install

npm install playwright-performance-reporter --save-dev

or

yarn add playwright-performance-reporter --dev

Usage

Disable parallelism:

export default defineConfig({
  ...
  fullyParallel: false,
  workers: 1,
  ...
})

Setup Reporter

To register the reporter, include the code blow in your playwright config. Please see the subsections for more details about browser specific cases and advanced configurations. For a runnable setup, see example/playwright.config.ts.

import type { CDP, Options, Metric } from 'playwright-performance-reporter';
import { nativeChromiumObservers } from 'playwright-performance-reporter';

const PlaywrightPerformanceReporterOptions: Options = {
  deleteOnFailure: false,
  browsers: {
    chromium: {
      onTestStep: {
        metrics: [new nativeChromiumObservers.allPerformanceMetrics()],
      }
    }
  }
}

export default defineConfig({
  ...
  reporter: [
    ['playwright-performance-reporter', PlaywrightPerformanceReporterOptions]
  ],
  ...
});

Chromium

Following metrics are supported out of the box:

• usedJsHeapSize
• totalJsHeapSize
• allPerformanceMetrics
• heapDump
• heapProfilerSampling

The MetricsEngine relies on the Chrome DevTool Protocol (CDP), which can be accessed through HTTP and WebSocket. To allow for a connection, make sure to expose a port for the remote debugging. The reporter will try to extract that port during start-up.

Setup Browser

{
  name: 'chromium',
  use: {
      ...devices['Desktop Chrome'],
    launchOptions: {
      args: [
        '--remote-debugging-port=9222'
      ]
    }
  }
},

Advanced Configurations

Sampling

Relying solely on the start and stop metric in a long running step leads to inaccuracies and requires a large set of runs to have a meaningful amount of metrics. By registering a metric to be collected every samplingTimeoutInMilliseconds the sampling output will be written to samplingMetrics, similar to startMetrics or startMetrics.

import { nativeChromiumObservers } from 'playwright-performance-reporter';

const PlaywrightPerformanceReporterOptions: Options = {
  ...
  browsers: {
    chromium: {
      onTestStep: {
        metrics: [new nativeChromiumObservers.usedJsHeapSize(), new nativeChromiumObservers.totalJsHeapSize()],
      },
      sampling: {
        metrics: [
          {
            samplingTimeoutInMilliseconds: 1000,
            metric: new nativeChromiumObservers.totalJsHeapSize()
          }
        ]
      }
    }
  }
}

Custom Metric Observer

If you want to extend it with custom metrics, you can create a new class that implements the MetricObserver interface. Please see the example below how to use it, or checkout the allPerformanceMetrics implementation.

For ease of implementation, the passed object can implement the interface ChromiumMetricObserver, WebkitMetricObserver or FirefoxMetricObserver. By using custom metrics it's possible to make observers stateful and e.g. make the next output dependent on the previous one.

import type { ChromiumMetricObserver, Options } from 'playwright-performance-reporter';

class NewMetric implements ChromiumMetricObserver {
  ...
}

const PlaywrightPerformanceReporterOptions: Options = {
  outputDir: '/your/path/to/dir',
  outputFile: 'output.json',
  deleteOnFailure: false,
  browsers: {
    chromium: {
      onTestStep: {
        metrics: [new NewMetric()]
      }
    }
  }
}

Presenters

Presenters allow multiple output formats to be generated simultaneously from the same test data. Each presenter receives the same data and can transform it into a different format.

In the example project, two presenters are configured and generate:

• example/example-json-writer.json
• example/example-chart-presenter.html

How Presenters Work

• Multiple presenters can be registered in the presenters array
• Each presenter is initialized with the same output configuration
• Every metric write is broadcast to all presenters
• Each presenter handles its own file writing, closing, and deletion

Using Predefined Presenters

The library provides two built-in presenters:

import { presenters } from 'playwright-performance-reporter';

const options: Options = {
  presenters: [
    new presenters.jsonChunkWriter(...),
    new presenters.chartPresenter(...)
  ],
  ...
}

Custom Presenters

The output is sent in chunks to the presenter(s) defined in the options. If there is a need to provide a custom writer, then the presenters is of help to customize how the chunks are handled. Every new entry is sent to the write function. Once the test is complete close is called. In case the test failed and deleteOnFailure === true, then the delete function is called.

import type { PresenterWriter, ResultAccumulator } from 'playwright-performance-reporter';

class CustomJsonWriter implements PresenterWriter {
  async write(content: ResultAccumulator): Promise<boolean> {
    // Write content
    return true;
  }

  async close(): Promise<boolean> {
    // Close the writer
    return true;
  }

  async delete(): Promise<boolean> {
    // Delete the created file
    return true;
  }
}

const PlaywrightPerformanceReporterOptions: Options = {
  deleteOnFailure: true,
  presenters: [new CustomJsonWriter()],
  ...
}

Output

Check example/ for the real-world setup. If you run the example simulation (cd example && npm run test), output is written to:

• example/example-json-writer.json (jsonChunkPresenter output)
• example/example-chart-presenter.html (chartPresenter output)

The top level is hooked into test().

{
  ...
  "4dde6239d9ac8c9468f3-82e3094b06379c51b729": {
    "TEST_CASE_PARENT": {
      "name": " > chromium > scenarios/profile.spec.ts > Profile",
      ...
    }
    ...
  }
  ...
}

The content consists of steps of the test suite. Please keep in mind that the metric request is async and is not awaited by Playwright. This means that the browser API might still in the process of collecting the metrics, even though Playwright instructed the browser to continue to the next step. This could lead to wrong output. To check if the output is invalid, the values startMeasurementOffset and endMeasurementOffset are provided, which measure the time delta in milliseconds between the request until the browser provides all metrics.