code: function assertFieldExists(name, message, cb) {
          if (!cb) {
              cb = message;
              message = "assertFieldExists";
          }
  
          this.isExisting(_.template('[name=<%= name %>]', {name: JSON.stringify(name)}), function (err, isExisting) {
              try {
                  if (err) {throw err;}
                  expect(isExisting).to.be.true;
                  cb();
              } catch (e) {
                  cb(new VError(e, message));
              }
          });
      }
docs: Form