assertCb = function(
        methodName, context, self, data, opt_resp, opt_error) {
      var p = new GoogPromise(function(resolve, reject) {
        self.expectedCalls_.push({
          'methodName': methodName,
          'data': data,
          'resp': opt_resp,
          'error': opt_error,
          'resolveAssert': resolve
        });
        // This API has already been called but not processed yet. Resolve
        // returned promise.
        if (self.actualCalls_[methodName] &&
            self.actualCalls_[methodName].length > 0) {
          resolve();
        }
      });
      // Returns a promise that resolves when this API is called.
      // This is useful if this API is called asynchronously.
      return p;
    }
@private {!Array<!Object>} The array of expected calls made.