test/shared/screenshots.ts - devtools/devtools-frontend - Git at Google

 // Copyright 2023 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 /* eslint-disable no-console */
 // no-console disabled here as this is a test runner and expects to output to the console

 import {assert} from 'chai';
 import * as childProcess from 'node:child_process';
 import * as fs from 'node:fs';
 import * as path from 'node:path';
 import type * as puppeteer from 'puppeteer-core';

 import {SOURCE_ROOT} from '../conductor/paths.js';
 import {platform} from '../conductor/platform.js';
 import {ScreenshotError} from '../conductor/screenshot-error.js';
 import {TestConfig} from '../conductor/test_config.js';
 import {getBrowserAndPages} from '../shared/helper.js';

 /**
  * The goldens screenshot folder is always taken from the source directory (NOT
  * out/Target/...) because we commit these files to git. Therefore we use the
  * flags from the test runner config to locate the source directory and read our
  * goldens from there.
  */
 const testRunnerCWD = SOURCE_ROOT;
 const GOLDENS_FOLDER = path.join(testRunnerCWD, 'test', 'goldens', platform);

 /**
  * It's assumed that the image_diff binaries are in CWD/third_party/image_diff/{platform}/image_diff
  */
 const exeSuffix = platform.startsWith('win') ? '.exe' : '';
 const IMAGE_DIFF_BINARY = path.join(testRunnerCWD, 'third_party', 'image_diff', platform, 'image_diff' + exeSuffix);
 if (!fs.existsSync(IMAGE_DIFF_BINARY)) {
   throw new Error(`path to image_diff (${IMAGE_DIFF_BINARY}) did not exist.`);
 }

 /**
  * The generated screenshot path is relative, as we put the generated
  * screenshots into the out/TARGET/... directory.
  *
  * If we find it exists ahead of a test run, we remove it, so that when we start
  * a test run the folder is empty. This ensures no generated files left from
  * previous runs interfere.
  */
 const generatedScreenshotFolderParts = ['..', '.generated', platform];
 const generatedScreenshotFolder = path.join(__dirname, ...generatedScreenshotFolderParts);
 if (fs.existsSync(generatedScreenshotFolder)) {
   fs.rmSync(generatedScreenshotFolder, {recursive: true});
 }
 fs.mkdirSync(generatedScreenshotFolder, {recursive: true});

 const defaultScreenshotOpts: puppeteer.ScreenshotOptions = {
   type: 'png',
   encoding: 'binary',
   captureBeyondViewport: false,
 };

 const DEFAULT_RETRIES_COUNT = 1;
 const DEFAULT_MS_BETWEEN_RETRIES = 150;

 // Percentage difference when comparing golden vs new screenshot that is
 // acceptable and will not fail the test.
 const DEFAULT_SCREENSHOT_THRESHOLD_PERCENT = 0.1;

 export const assertElementScreenshotUnchanged = async (
     element: puppeteer.ElementHandle|null,
     fileName: NonNullable<puppeteer.ScreenshotOptions['path']>,
     options: Partial<puppeteer.ScreenshotOptions> = {},
     ) => {
   assert.isOk(element, `Given element for test ${fileName} was not found.`);
   // Only assert screenshots on Linux. We don't observe platform-specific differences enough to justify
   // the costs of asserting 3 platforms per screenshot.
   if (platform !== 'linux') {
     // Extra new line to work with the progress-diff karma reporter that
     // replaces the previous line.
     console.warn('Screenshot assertions are only supported on Linux\n');
     return;
   }
   return await assertScreenshotUnchangedWithRetries(
       element, fileName, DEFAULT_SCREENSHOT_THRESHOLD_PERCENT, DEFAULT_RETRIES_COUNT, options);
 };

 function getFrontend() {
   // Outside e2e or interaction tests the frontend can be undefined.
   try {
     const {frontend} = getBrowserAndPages();
     return frontend;
   } catch {
     return;
   }
 }

 const assertScreenshotUnchangedWithRetries = async (
     elementOrPage: puppeteer.ElementHandle|puppeteer.Page, fileName: NonNullable<puppeteer.ScreenshotOptions['path']>,
     maximumDiffThreshold: number, maximumRetries: number, options: Partial<puppeteer.ScreenshotOptions> = {}) => {
   const frontend = getFrontend();
   try {
     await frontend?.evaluate(() => window.dispatchEvent(new Event('hidecomponentdocsui')));
     /**
      * You can call the helper with a path for the golden - e.g.
      * accordion/basic.png. So we split on `/` and then join on path.sep to
      * ensure we calculate the right path regardless of platform.
      */
     const fileNameForPlatform = fileName.split('/').join(path.sep);
     const goldenScreenshotPath = path.join(GOLDENS_FOLDER, fileNameForPlatform);
     const generatedScreenshotPath =
         path.join(generatedScreenshotFolder, fileNameForPlatform) as NonNullable<puppeteer.ScreenshotOptions['path']>;

     /**
      * Ensure that the directories for the golden/generated file exist. We need
      * this because if the user calls this function with `accordion/basic.png`,
      * we need to make sure that the `accordion` folder exists.
      */
     fs.mkdirSync(path.dirname(generatedScreenshotPath), {recursive: true});
     fs.mkdirSync(path.dirname(goldenScreenshotPath), {recursive: true});

     await assertScreenshotUnchanged({
       elementOrPage,
       generatedScreenshotPath,
       goldenScreenshotPath,
       screenshotOptions: options,
       fileName,
       maximumDiffThreshold,
       maximumRetries,
     });
   } finally {
     await frontend?.evaluate(() => window.dispatchEvent(new Event('showcomponentdocsui')));
   }
 };

 interface ScreenshotAssertionOptions {
   goldenScreenshotPath: string;
   generatedScreenshotPath: NonNullable<puppeteer.ScreenshotOptions['path']>;
   screenshotOptions: Partial<puppeteer.ScreenshotOptions>;
   elementOrPage: puppeteer.ElementHandle|puppeteer.Page;
   fileName: string;
   maximumDiffThreshold: number;
   maximumRetries: number;
   retryCount?: number;
 }

 const assertScreenshotUnchanged = async (options: ScreenshotAssertionOptions) => {
   const {
     elementOrPage,
     generatedScreenshotPath,
     goldenScreenshotPath,
     fileName,
     maximumDiffThreshold,
     maximumRetries,
     retryCount = 1,
   } = options;
   const screenshotOptions = {...defaultScreenshotOpts, ...options.screenshotOptions, path: generatedScreenshotPath};
   await elementOrPage.screenshot(screenshotOptions);

   /**
    * The user can do UPDATE_GOLDEN=accordion/basic.png npm run screenshotstest
    * to update the golden image. This is useful if work has caused the
    * screenshot to change and therefore the test goldens need to be updated.
    */
   const shouldUpdate =
       TestConfig.onDiff.update && (TestConfig.onDiff.update === true || TestConfig.onDiff.update.includes(fileName));
   const throwAfterGoldensUpdate = TestConfig.onDiff.throw;

   let onBotAndImageNotFound = false;

   // In the event that a golden does not exist, assume the generated screenshot is the new golden.
   if (!fs.existsSync(goldenScreenshotPath)) {
     // LUCI_CONTEXT is an environment variable present on the bots.
     if (process.env.LUCI_CONTEXT !== undefined && !shouldUpdate) {
       // If the image is missing, there's no point retrying the test N more times.
       onBotAndImageNotFound = true;
       throw ScreenshotError.fromGeneratedScreenshot(
           `Failing test: in an environment with LUCI_CONTEXT and did not find a golden screenshot.

         Here's the image that this test generated as a base64:

         data:image/png;base64,${fs.readFileSync(generatedScreenshotPath, {
             encoding: 'base64',
           })}
         `,
           generatedScreenshotPath);
     }

     console.log('Golden does not exist, using generated screenshot.');
     setGeneratedFileAsGolden(goldenScreenshotPath, generatedScreenshotPath);
     if (throwAfterGoldensUpdate) {
       throw ScreenshotError.fromGeneratedScreenshot(
           'Golden does not exist, using generated screenshot.', generatedScreenshotPath);
     }
   }

   try {
     await compare(goldenScreenshotPath, generatedScreenshotPath, maximumDiffThreshold, shouldUpdate);
   } catch (compareError) {
     if (!onBotAndImageNotFound) {
       console.log(`=> Test failed. Retrying (retry ${retryCount} of ${maximumRetries} maximum).`);
     }

     if (retryCount === maximumRetries || onBotAndImageNotFound) {
       if (shouldUpdate) {
         console.log(`=> ${fileName} was out of date and failed; updating`);
         setGeneratedFileAsGolden(goldenScreenshotPath, generatedScreenshotPath);
         if (throwAfterGoldensUpdate) {
           throw compareError;
         }
         return;
       }
       // If we don't want to update, throw the assertion error so we fail the test.
       throw compareError;
     }

     // Wait a little bit before trying again
     await new Promise(resolve => setTimeout(resolve, DEFAULT_MS_BETWEEN_RETRIES));

     await assertScreenshotUnchanged({
       elementOrPage,
       generatedScreenshotPath,
       goldenScreenshotPath,
       fileName,
       maximumDiffThreshold,
       maximumRetries,
       retryCount: retryCount + 1,
       screenshotOptions: options.screenshotOptions,
     });
   }
 };

 interface ImageDiff {
   rawMisMatchPercentage: number;
   diffPath: string;
 }

 async function imageDiff(golden: string, generated: string) {
   return await new Promise<ImageDiff>(async (resolve, reject) => {
     try {
       const imageDiff: ImageDiff = {rawMisMatchPercentage: 0, diffPath: ''};
       const diffText = await execImageDiffCommand(`${IMAGE_DIFF_BINARY} --histogram ${golden} ${generated}`);

       // Parse out the number from the cmd output, i.e. diff: 48.9% failed => 48.9
       imageDiff.rawMisMatchPercentage = Number(diffText.replace(/^diff:\s/, '').replace(/%.*/, ''));

       if (Number.isNaN(imageDiff.rawMisMatchPercentage)) {
         reject('Unable to compare images');
       }

       // Only create a diff image if the images are different.
       if (imageDiff.rawMisMatchPercentage > 0) {
         imageDiff.diffPath = path.join(path.dirname(generated), `${path.basename(generated, '.png')}-diff.png`);
         await execImageDiffCommand(`${IMAGE_DIFF_BINARY} --diff ${golden} ${generated} ${imageDiff.diffPath}`);
       }

       resolve(imageDiff);
     } catch (e) {
       reject(new Error(`Error when running image_diff: ${e.stack}`));
     }
   });
 }

 async function execImageDiffCommand(cmd: string) {
   return await new Promise<string>((resolve, reject) => {
     let commandOutput = '';
     try {
       commandOutput = childProcess.execSync(cmd, {encoding: 'utf8'});
       resolve(commandOutput);
     } catch (e) {
       // image_diff will exit with a status code of 1 if the diff is too big, so
       // this needs to be caught, but the outcome is the same - we want to send
       // back the string for processing.
       if (e.stdout && e.stdout.indexOf('diff') === -1) {
         reject(new Error(`Comparing diff failed. stdout: "${e.stdout}"`));
         return;
       }

       resolve(e.stdout);
     }
   });
 }

 async function compare(golden: string, generated: string, maximumDiffThreshold: number, isInDiffUpdateMode: boolean) {
   const isOnBot = process.env.LUCI_CONTEXT !== undefined;
   if (!isOnBot && process.env.SKIP_SCREENSHOT_COMPARISONS_FOR_FAST_COVERAGE) {
     // When checking test coverage locally the tests get sped up significantly
     // if we do not do the actual image comparison. Obviously this makes the
     // tests all pass, but it is useful to quickly get coverage stats.
     // Therefore you can pass this flag to skip all screenshot comparisions. We
     // make sure this is only possible if not on a CQ bot and 99.9% of the time
     // this should not be used!
     return;
   }

   const {rawMisMatchPercentage, diffPath} = await imageDiff(golden, generated);

   const base64TestGeneratedImageLog = `Here's the image the test generated as a base64:
     data:image/png;base64,${fs.readFileSync(generated, {
     encoding: 'base64',
   })}`;

   const base64DiffImageLog = `And here's the diff image as base64:\n
     data:image/png;base64,${
       diffPath ? fs.readFileSync(diffPath, {
         encoding: 'base64',
       }) :
                  ''}`;

   let debugInfo = '';
   if (isOnBot) {
     debugInfo = `${base64TestGeneratedImageLog}\n${base64DiffImageLog}\n`;
   } else if (!isInDiffUpdateMode) {
     debugInfo = `Run the tests again with --on-diff=update to update all tests that fail.
   Only do this if you expected this screenshot to have changed!

   Diff image generated at:
   => ${path.relative(testRunnerCWD, diffPath)}\n`;
   }

   try {
     assert.isAtMost(
         rawMisMatchPercentage, maximumDiffThreshold,
         `There is a ${rawMisMatchPercentage}% difference between the golden and generated image.

     ${debugInfo}`);
     if (rawMisMatchPercentage > 0) {
       console.log(`test passed with difference of ${rawMisMatchPercentage}%`);
     }

   } catch (assertionError) {
     throw ScreenshotError.fromScreenshotAssertionError(assertionError, golden, generated, diffPath);
   }
 }

 function setGeneratedFileAsGolden(golden: string, generated: string) {
   console.log(`Setting generated file to golden:
   ${path.relative(testRunnerCWD, generated)}
   => ${path.relative(testRunnerCWD, golden)}
   `);
   try {
     fs.copyFileSync(generated, golden);
   } catch (e) {
     assert.fail(`Error setting golden, ${e}`);
   }
 }
	// Copyright 2023 The Chromium Authors
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	/* eslint-disable no-console */
	// no-console disabled here as this is a test runner and expects to output to the console

	import {assert} from 'chai';
	import * as childProcess from 'node:child_process';
	import * as fs from 'node:fs';
	import * as path from 'node:path';
	import type * as puppeteer from 'puppeteer-core';

	import {SOURCE_ROOT} from '../conductor/paths.js';
	import {platform} from '../conductor/platform.js';
	import {ScreenshotError} from '../conductor/screenshot-error.js';
	import {TestConfig} from '../conductor/test_config.js';
	import {getBrowserAndPages} from '../shared/helper.js';

	/**
	* The goldens screenshot folder is always taken from the source directory (NOT
	* out/Target/...) because we commit these files to git. Therefore we use the
	* flags from the test runner config to locate the source directory and read our
	* goldens from there.
	*/
	const testRunnerCWD = SOURCE_ROOT;
	const GOLDENS_FOLDER = path.join(testRunnerCWD, 'test', 'goldens', platform);

	/**
	* It's assumed that the image_diff binaries are in CWD/third_party/image_diff/{platform}/image_diff
	*/
	const exeSuffix = platform.startsWith('win') ? '.exe' : '';
	const IMAGE_DIFF_BINARY = path.join(testRunnerCWD, 'third_party', 'image_diff', platform, 'image_diff' + exeSuffix);
	if (!fs.existsSync(IMAGE_DIFF_BINARY)) {
	throw new Error(`path to image_diff (${IMAGE_DIFF_BINARY}) did not exist.`);
	}

	/**
	* The generated screenshot path is relative, as we put the generated
	* screenshots into the out/TARGET/... directory.
	*
	* If we find it exists ahead of a test run, we remove it, so that when we start
	* a test run the folder is empty. This ensures no generated files left from
	* previous runs interfere.
	*/
	const generatedScreenshotFolderParts = ['..', '.generated', platform];
	const generatedScreenshotFolder = path.join(__dirname, ...generatedScreenshotFolderParts);
	if (fs.existsSync(generatedScreenshotFolder)) {
	fs.rmSync(generatedScreenshotFolder, {recursive: true});
	}
	fs.mkdirSync(generatedScreenshotFolder, {recursive: true});

	const defaultScreenshotOpts: puppeteer.ScreenshotOptions = {
	type: 'png',
	encoding: 'binary',
	captureBeyondViewport: false,
	};

	const DEFAULT_RETRIES_COUNT = 1;
	const DEFAULT_MS_BETWEEN_RETRIES = 150;

	// Percentage difference when comparing golden vs new screenshot that is
	// acceptable and will not fail the test.
	const DEFAULT_SCREENSHOT_THRESHOLD_PERCENT = 0.1;

	export const assertElementScreenshotUnchanged = async (
	element: puppeteer.ElementHandle\|null,
	fileName: NonNullable<puppeteer.ScreenshotOptions['path']>,
	options: Partial<puppeteer.ScreenshotOptions> = {},
	) => {
	assert.isOk(element, `Given element for test ${fileName} was not found.`);
	// Only assert screenshots on Linux. We don't observe platform-specific differences enough to justify
	// the costs of asserting 3 platforms per screenshot.
	if (platform !== 'linux') {
	// Extra new line to work with the progress-diff karma reporter that
	// replaces the previous line.
	console.warn('Screenshot assertions are only supported on Linux\n');
	return;
	}
	return await assertScreenshotUnchangedWithRetries(
	element, fileName, DEFAULT_SCREENSHOT_THRESHOLD_PERCENT, DEFAULT_RETRIES_COUNT, options);
	};

	function getFrontend() {
	// Outside e2e or interaction tests the frontend can be undefined.
	try {
	const {frontend} = getBrowserAndPages();
	return frontend;
	} catch {
	return;
	}
	}

	const assertScreenshotUnchangedWithRetries = async (
	elementOrPage: puppeteer.ElementHandle\|puppeteer.Page, fileName: NonNullable<puppeteer.ScreenshotOptions['path']>,
	maximumDiffThreshold: number, maximumRetries: number, options: Partial<puppeteer.ScreenshotOptions> = {}) => {
	const frontend = getFrontend();
	try {
	await frontend?.evaluate(() => window.dispatchEvent(new Event('hidecomponentdocsui')));
	/**
	* You can call the helper with a path for the golden - e.g.
	* accordion/basic.png. So we split on `/` and then join on path.sep to
	* ensure we calculate the right path regardless of platform.
	*/
	const fileNameForPlatform = fileName.split('/').join(path.sep);
	const goldenScreenshotPath = path.join(GOLDENS_FOLDER, fileNameForPlatform);
	const generatedScreenshotPath =
	path.join(generatedScreenshotFolder, fileNameForPlatform) as NonNullable<puppeteer.ScreenshotOptions['path']>;

	/**
	* Ensure that the directories for the golden/generated file exist. We need
	* this because if the user calls this function with `accordion/basic.png`,
	* we need to make sure that the `accordion` folder exists.
	*/
	fs.mkdirSync(path.dirname(generatedScreenshotPath), {recursive: true});
	fs.mkdirSync(path.dirname(goldenScreenshotPath), {recursive: true});

	await assertScreenshotUnchanged({
	elementOrPage,
	generatedScreenshotPath,
	goldenScreenshotPath,
	screenshotOptions: options,
	fileName,
	maximumDiffThreshold,
	maximumRetries,
	});
	} finally {
	await frontend?.evaluate(() => window.dispatchEvent(new Event('showcomponentdocsui')));
	}
	};

	interface ScreenshotAssertionOptions {
	goldenScreenshotPath: string;
	generatedScreenshotPath: NonNullable<puppeteer.ScreenshotOptions['path']>;
	screenshotOptions: Partial<puppeteer.ScreenshotOptions>;
	elementOrPage: puppeteer.ElementHandle\|puppeteer.Page;
	fileName: string;
	maximumDiffThreshold: number;
	maximumRetries: number;
	retryCount?: number;
	}

	const assertScreenshotUnchanged = async (options: ScreenshotAssertionOptions) => {
	const {
	elementOrPage,
	generatedScreenshotPath,
	goldenScreenshotPath,
	fileName,
	maximumDiffThreshold,
	maximumRetries,
	retryCount = 1,
	} = options;
	const screenshotOptions = {...defaultScreenshotOpts, ...options.screenshotOptions, path: generatedScreenshotPath};
	await elementOrPage.screenshot(screenshotOptions);

	/**
	* The user can do UPDATE_GOLDEN=accordion/basic.png npm run screenshotstest
	* to update the golden image. This is useful if work has caused the
	* screenshot to change and therefore the test goldens need to be updated.
	*/
	const shouldUpdate =
	TestConfig.onDiff.update && (TestConfig.onDiff.update === true \|\| TestConfig.onDiff.update.includes(fileName));
	const throwAfterGoldensUpdate = TestConfig.onDiff.throw;

	let onBotAndImageNotFound = false;

	// In the event that a golden does not exist, assume the generated screenshot is the new golden.
	if (!fs.existsSync(goldenScreenshotPath)) {
	// LUCI_CONTEXT is an environment variable present on the bots.
	if (process.env.LUCI_CONTEXT !== undefined && !shouldUpdate) {
	// If the image is missing, there's no point retrying the test N more times.
	onBotAndImageNotFound = true;
	throw ScreenshotError.fromGeneratedScreenshot(
	`Failing test: in an environment with LUCI_CONTEXT and did not find a golden screenshot.

	Here's the image that this test generated as a base64:

	data:image/png;base64,${fs.readFileSync(generatedScreenshotPath, {
	encoding: 'base64',
	})}
	`,
	generatedScreenshotPath);
	}

	console.log('Golden does not exist, using generated screenshot.');
	setGeneratedFileAsGolden(goldenScreenshotPath, generatedScreenshotPath);
	if (throwAfterGoldensUpdate) {
	throw ScreenshotError.fromGeneratedScreenshot(
	'Golden does not exist, using generated screenshot.', generatedScreenshotPath);
	}
	}

	try {
	await compare(goldenScreenshotPath, generatedScreenshotPath, maximumDiffThreshold, shouldUpdate);
	} catch (compareError) {
	if (!onBotAndImageNotFound) {
	console.log(`=> Test failed. Retrying (retry ${retryCount} of ${maximumRetries} maximum).`);
	}

	if (retryCount === maximumRetries \|\| onBotAndImageNotFound) {
	if (shouldUpdate) {
	console.log(`=> ${fileName} was out of date and failed; updating`);
	setGeneratedFileAsGolden(goldenScreenshotPath, generatedScreenshotPath);
	if (throwAfterGoldensUpdate) {
	throw compareError;
	}
	return;
	}
	// If we don't want to update, throw the assertion error so we fail the test.
	throw compareError;
	}

	// Wait a little bit before trying again
	await new Promise(resolve => setTimeout(resolve, DEFAULT_MS_BETWEEN_RETRIES));

	await assertScreenshotUnchanged({
	elementOrPage,
	generatedScreenshotPath,
	goldenScreenshotPath,
	fileName,
	maximumDiffThreshold,
	maximumRetries,
	retryCount: retryCount + 1,
	screenshotOptions: options.screenshotOptions,
	});
	}
	};

	interface ImageDiff {
	rawMisMatchPercentage: number;
	diffPath: string;
	}

	async function imageDiff(golden: string, generated: string) {
	return await new Promise<ImageDiff>(async (resolve, reject) => {
	try {
	const imageDiff: ImageDiff = {rawMisMatchPercentage: 0, diffPath: ''};
	const diffText = await execImageDiffCommand(`${IMAGE_DIFF_BINARY} --histogram ${golden} ${generated}`);

	// Parse out the number from the cmd output, i.e. diff: 48.9% failed => 48.9
	imageDiff.rawMisMatchPercentage = Number(diffText.replace(/^diff:\s/, '').replace(/%.*/, ''));

	if (Number.isNaN(imageDiff.rawMisMatchPercentage)) {
	reject('Unable to compare images');
	}

	// Only create a diff image if the images are different.
	if (imageDiff.rawMisMatchPercentage > 0) {
	imageDiff.diffPath = path.join(path.dirname(generated), `${path.basename(generated, '.png')}-diff.png`);
	await execImageDiffCommand(`${IMAGE_DIFF_BINARY} --diff ${golden} ${generated} ${imageDiff.diffPath}`);
	}

	resolve(imageDiff);
	} catch (e) {
	reject(new Error(`Error when running image_diff: ${e.stack}`));
	}
	});
	}

	async function execImageDiffCommand(cmd: string) {
	return await new Promise<string>((resolve, reject) => {
	let commandOutput = '';
	try {
	commandOutput = childProcess.execSync(cmd, {encoding: 'utf8'});
	resolve(commandOutput);
	} catch (e) {
	// image_diff will exit with a status code of 1 if the diff is too big, so
	// this needs to be caught, but the outcome is the same - we want to send
	// back the string for processing.
	if (e.stdout && e.stdout.indexOf('diff') === -1) {
	reject(new Error(`Comparing diff failed. stdout: "${e.stdout}"`));
	return;
	}

	resolve(e.stdout);
	}
	});
	}

	async function compare(golden: string, generated: string, maximumDiffThreshold: number, isInDiffUpdateMode: boolean) {
	const isOnBot = process.env.LUCI_CONTEXT !== undefined;
	if (!isOnBot && process.env.SKIP_SCREENSHOT_COMPARISONS_FOR_FAST_COVERAGE) {
	// When checking test coverage locally the tests get sped up significantly
	// if we do not do the actual image comparison. Obviously this makes the
	// tests all pass, but it is useful to quickly get coverage stats.
	// Therefore you can pass this flag to skip all screenshot comparisions. We
	// make sure this is only possible if not on a CQ bot and 99.9% of the time
	// this should not be used!
	return;
	}

	const {rawMisMatchPercentage, diffPath} = await imageDiff(golden, generated);

	const base64TestGeneratedImageLog = `Here's the image the test generated as a base64:
	data:image/png;base64,${fs.readFileSync(generated, {
	encoding: 'base64',
	})}`;

	const base64DiffImageLog = `And here's the diff image as base64:\n
	data:image/png;base64,${
	diffPath ? fs.readFileSync(diffPath, {
	encoding: 'base64',
	}) :
	''}`;

	let debugInfo = '';
	if (isOnBot) {
	debugInfo = `${base64TestGeneratedImageLog}\n${base64DiffImageLog}\n`;
	} else if (!isInDiffUpdateMode) {
	debugInfo = `Run the tests again with --on-diff=update to update all tests that fail.
	Only do this if you expected this screenshot to have changed!

	Diff image generated at:
	=> ${path.relative(testRunnerCWD, diffPath)}\n`;
	}

	try {
	assert.isAtMost(
	rawMisMatchPercentage, maximumDiffThreshold,
	`There is a ${rawMisMatchPercentage}% difference between the golden and generated image.

	${debugInfo}`);
	if (rawMisMatchPercentage > 0) {
	console.log(`test passed with difference of ${rawMisMatchPercentage}%`);
	}

	} catch (assertionError) {
	throw ScreenshotError.fromScreenshotAssertionError(assertionError, golden, generated, diffPath);
	}
	}

	function setGeneratedFileAsGolden(golden: string, generated: string) {
	console.log(`Setting generated file to golden:
	${path.relative(testRunnerCWD, generated)}
	=> ${path.relative(testRunnerCWD, golden)}
	`);
	try {
	fs.copyFileSync(generated, golden);
	} catch (e) {
	assert.fail(`Error setting golden, ${e}`);
	}
	}