code: function(karmaSettings, resolveFn) {
          var testServer = new karma.Server(karmaSettings, function(exitCode) {
              if (typeof(resolveFn) === 'function') {
                  resolveFn(exitCode);
              } else {
                  process.exit(exitCode);
              }
          });
  
          testServer.start();
      }
docs: Run the test suite with the supplied settings and
  callback function.
  
  @param {Object} karmaSettings - Options for Karma.
  @param {Function} resolveFn - Gulp async function.