code: func (c *MockClient) Increment(
  	key string,
  	delta uint64,
  	initValue uint64,
  	expiration uint32) CountResponse {
  
  	c.mutex.Lock()
  	defer c.mutex.Unlock()
  	return c.incrementDecrementHelper(key, delta, initValue, expiration, Increment)
  
  }
docs: // This increments the key's counter by delta.  If the counter does not
  // exist, one of two things may happen:
  // 1. If the expiration value is all one-bits (0xffffffff), the operation
  // will fail with StatusNotFound.
  // 2. For all other expiration values, the operation will succeed by
  // seeding the value for this key with the provided initValue to expire
  // with the provided expiration time. The flags will be set to zero.
  //
  // NOTE:
  // 1. If you want to set the value of the counter with add/set/replace,
  // the objects data must be the ascii representation of the value and
  // not the byte values of a 64 bit integer.
  // 2. Incrementing the counter may cause the counter to wrap.