function getFiles() {
  gutil.log(' Searching for files...');
  if (global.WF.options.testPath || global.WF.options.testAll) {
    return new Promise(function(resolve, reject) {
      let globs = ['./gulp-tasks/**/*', './gulpfile.js'];
      let opts = {
        prefixBase: true,
        filter: 'isFile',
      };
      if (global.WF.options.testPath) {
        const testPath = global.WF.options.testPath;
        if (global.WF.options.verbose) {
          gutil.log(' ', 'Searching for files in', chalk.cyan(testPath));
        }
        opts.srcBase = global.WF.options.testPath;
        globs.push('**/*');
      } else {
        opts.srcBase = './src/content';
        global.WF.options.lang.forEach(function(lang) {
          const testPath = `${opts.srcBase}/${lang}`;
          if (global.WF.options.verbose) {
            gutil.log(' ', 'Searching for files in', chalk.cyan(testPath));
          }
          globs.push(`${lang}/**/*`);
        });
      }
      // Skip Puppeteer docs
      globs.push('!en/tools/puppeteer/_src/**/*');
      // Skip any _README.MD files
      globs.push('!_README.MD');
      resolve(glob.find(globs, opts));
    });
  } else {
    gutil.log(' ', 'Searching for changed files');
    let cmd = 'git --no-pager diff --name-only ';
    if (IS_TRAVIS) {
      cmd += '$(git merge-base FETCH_HEAD main) FETCH_HEAD';
    } else {
      cmd += '$(git merge-base origin/main HEAD)';
    }
    return wfHelper.promisedExec(cmd, '.')
    .then(function(results) {
      let files = [];
      let warnForSideEffect = false;
      results.split('\n').forEach(function(filename) {
        if (RE_GULP_BASE.test(filename) || filename === 'gulpfile.js') {
          warnForSideEffect = true;
          files.push(filename);
        } else if (RE_SRC_BASE.test(filename) || RE_DATA_BASE.test(filename) ||
                   filename === 'app.yaml') {
          files.push(filename);
        }
      });
      if (warnForSideEffect === true) {
        const warn = chalk.yellow('WARNING:');
        const msg = `Gulp tasks have changed, be sure to run with ` +
          `${chalk.cyan('--testAll')} or ${chalk.cyan('--testMain')} ` +
          `to catch any unintended side effects!`;
        gutil.log(warn, msg);
      }
      const warnMsg = `More than ${MAX_FILES_CHANGED_WARNING} files changed.`;
      if (files.length > MAX_FILES_CHANGED_ERROR) {
        const msg = `Maxiumum number of changed files exceeeded.`;
        logError('', null, `${msg} ${warnMsg}`);
      } else if (files.length > MAX_FILES_CHANGED_WARNING) {
        logWarning('', null, `${warnMsg}`);
      }
      return files;
    });
  }
}
Gets a list of all files to be tested.

@return {Promise} The list of files