docs: function isolate(fn, val) {
      var value, lastPromise;
  
      // Reset lastPromise for nested helpers
      Test.lastPromise = null;
  
      value = fn(val);
  
      lastPromise = Test.lastPromise;
      Test.lastPromise = null;
  
      // If the method returned a promise
      // return that promise. If not,
      // return the last async helper's promise
      if (value && value instanceof Test.Promise || !lastPromise) {
        return value;
      } else {
        return run(function () {
          return Test.resolve(lastPromise).then(function () {
            return value;
          });
        });
      }
    }