async function printDiff(testName, testString, api, options) {
  let j = api.jscodeshift;
  let test = j(testString);
  // Suppress redundant verbose output while generating the diff.
  let opts = {...options, verbose: false};
  let fixturePaths = findFixturePaths(test, api, opts);
  let fixtures = await generateFsFixtures(fixturePaths, api, opts);
  if (fixtures.size) {
    insertFsFixtures(test, fixtures, api, opts);
    replaceInputFS(test, api, opts);
    replaceFixturePaths(fixturePaths, api, opts);
    console.log(
      diff
        .createTwoFilesPatch('before', 'after', testString, test.toSource())
        .split('\n')
        .map(line => {
          if (/^\++ /.test(line)) {
            return chalk.green(line);
          } else if (/^-+ /.test(line)) {
            return chalk.red(line);
          } else if (/^@+ /.test(line)) {
            return chalk.black(line);
          }
          return line;
        })
        .join('\n'),
    );
  }
}
Print a diff of the test before and after the transform.