A custom matcher for when you want to compare strings in Jest and ignore whitespace

customWhitespaceMatcher.js

// Modified version of this Stack Overflow response:
// https://stackoverflow.com/a/48459005/1950503
// (Removes ramda dependency, adds .trim() to string replacer, adds it to Jest global var instead of exporting)

// To use:
// Put `<rootDir>/path/to/customWhitespaceMatcher.js` in your Jest config under setupFiles
// Call it in your tests like this:
//    expect(
//      customMatchers.whitespaceMatcher(receivedResult, expectedResult).pass
//    ).toBeTruthy();

import { matcherHint, printReceived, printExpected } from 'jest-matcher-utils';
import diff from 'jest-diff';

const replaceWhitespace = str => str.replace(/\s+/g, ' ').trim();
const compressWhitespace = arr => arr.map(replaceWhitespace);

const name = `toEqualWithCompressedWhitespace`;

const whitespaceMatcher = (received, expected) => {
  const [
    receivedWithCompresssedWhitespace,
    expectedWithCompresssedWhitespace
  ] = compressWhitespace([received, expected]);
  let pass =
    receivedWithCompresssedWhitespace === expectedWithCompresssedWhitespace;

  const message = pass
    ? () =>
        `${matcherHint(`.not.${name}`)}\n\n` +
        `Uncompressed expected value:\n` +
        `  ${printExpected(expected)}\n` +
        `Expected value with compressed whitespace to not equal:\n` +
        `  ${printExpected(expectedWithCompresssedWhitespace)}\n` +
        `Uncompressed received value:\n` +
        `  ${printReceived(received)}\n` +
        `Received value with compressed whitespace:\n` +
        `  ${printReceived(receivedWithCompresssedWhitespace)}`
    : () => {
        const diffString = diff(
          expectedWithCompresssedWhitespace,
          receivedWithCompresssedWhitespace
        );
        return (
          `${matcherHint(`.${name}`)}\n\n` +
          `Uncompressed expected value:\n` +
          `  ${printExpected(expected)}\n` +
          `Expected value with compressed whitespace to equal:\n` +
          `  ${printExpected(expectedWithCompresssedWhitespace)}\n` +
          `Uncompressed received value:\n` +
          `  ${printReceived(received)}\n` +
          `Received value with compressed whitespace:\n` +
          `  ${printReceived(receivedWithCompresssedWhitespace)}${
            diffString ? `\n\nDifference:\n\n${diffString}` : ``
          }`
        );
      };
  return {
    actual: received,
    expected,
    message,
    name,
    pass
  };
};

global.customMatchers = { whitespaceMatcher };