message: test: improve diff
diff: @@ -13,19 +13,25 @@ type Received = Array<{
  code: string;
  }>;
  -expect.extend({
  - toMatchOutput(received: Received, output) {
  - const { isNot } = this;
  - const snapshotState = (this as any).snapshotState;
  - const actual = sortBy(received, ['fileName'])
  +function buildText(files: Received) {
  + return sortBy(files, ['fileName'])
  .reduce((acc: string[], f) => {
  acc.push(
  - f.fileName,
  - ...eol.split(f.code).map(l => l + ` // ${f.fileName}`)
  + `file: ${f.fileName}`,
  + Array(80).join('-'),
  + ...eol.split(f.code).map(l => l + ` // ${f.fileName}`),
  + Array(80).join('-')
  );
  return acc;
  }, [])
  .join(eol.auto.toString());
  +}
  +
  +expect.extend({
  + toMatchOutput(received: Received, output) {
  + const { isNot } = this;
  + const snapshotState = (this as any).snapshotState;
  + const actual = buildText(received);
  const options = {
  // Options for jest-diff
  @@ -37,23 +43,14 @@ expect.extend({
  };
  if (fs.existsSync(output)) {
  - const expected = sortBy(
  + const expected = buildText(
  readdir(output).map(fileName => ({
  fileName: slash(fileName),
  code: eol.lf(
  sander.readFileSync(path.join(output, fileName)).toString()
  ),
  - })),
  - 'fileName'
  - )
  - .reduce((acc: string[], f) => {
  - acc.push(
  - f.fileName,
  - ...eol.split(f.code).map(l => l + ` // ${f.fileName}`)
  + }))
  );
  - return acc;
  - }, [])
  - .join(eol.auto.toString());
  if (isNot) {
  // The matcher is being used with `.not`
  