@johnf/react-native-owl/lib/module/matchers.js

Visual regression testing for React Native

"use strict";

import fs from 'fs';
import path from 'path';
import pixelmatch from 'pixelmatch';
import { PNG } from 'pngjs';
export const toMatchBaseline = (latestPath, options = {
  threshold: 0.1,
  bottomCrop: 0
}) => {
  const platform = process.env.OWL_PLATFORM;
  const screenshotsDir = path.join(path.dirname(latestPath), '..', '..');
  const baselinePath = path.join(screenshotsDir, 'baseline', platform, path.basename(latestPath));
  if (latestPath === baselinePath) {
    return {
      message: () => 'Generated a fresh baseline, skipping comparison.',
      pass: true
    };
  }
  try {
    const diffPath = path.join(screenshotsDir, 'diff', platform, path.basename(latestPath));
    fs.mkdirSync(path.dirname(diffPath), {
      recursive: true
    });
    const baselineData = fs.readFileSync(baselinePath);
    const baselineImage = PNG.sync.read(baselineData);
    const croppedHeight = baselineImage.height - (options.bottomCrop || 0);
    const croppedBaselineImage = new PNG({
      width: baselineImage.width,
      height: croppedHeight
    });
    PNG.bitblt(baselineImage, croppedBaselineImage, 0, 0, baselineImage.width, croppedHeight, 0, 0);
    const latestData = fs.readFileSync(latestPath);
    const latestImage = PNG.sync.read(latestData);
    const croppedLatestImage = new PNG({
      width: baselineImage.width,
      height: croppedHeight
    });
    PNG.bitblt(latestImage, croppedLatestImage, 0, 0, baselineImage.width, croppedHeight, 0, 0);
    const diffImage = new PNG({
      width: baselineImage.width,
      height: croppedHeight
    });
    const diffPixelsCount = pixelmatch(croppedBaselineImage.data, croppedLatestImage.data, diffImage.data, baselineImage.width, croppedHeight, {
      threshold: options?.threshold
    });
    if (diffPixelsCount === 0) {
      return {
        message: () => `Compared screenshot to match baseline. No differences were found.`,
        pass: true
      };
    }

    // Create and save the diff image
    fs.writeFileSync(diffPath, PNG.sync.write(diffImage), {
      encoding: 'binary'
    });
    return {
      message: () => `Compared screenshot to match baseline. ${diffPixelsCount} were different.`,
      pass: diffPixelsCount === 0
    };
  } catch (error) {
    let message = 'Unknown error';
    if (error instanceof Error) {
      message = error.message;
    }
    return {
      message: () => `Screenshot diffing error - ${message}`,
      pass: false
    };
  }
};
expect.extend({
  toMatchBaseline
});
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