I've always had issues with the Turing Test, not because I disagree with equating computed intelligence with the ability to imitate intelligence, but simply because it equates intelligence with speaking skills. Obviously intelligence has numerous ways of expressing itself other than through speech. Apart from there being no reason for this particular expression of intelligence to be superior to other expressions of intelligence (provided it is a sufficiently powerful intelligence), the Turing Test is actually impeding the progress of artificial intelligence by diverting attention to natural language processing rather than pure artificial intelligence.
The fact is that a sufficiently intelligent organism will learn to communicate with us in whatever way is most appropriate for it, even if it is not in English, just like a dog would. Communication is a consequence of intelligence rather than the other way round. So what I'm saying is that we should focus on developing pure artificial intelligence rather than chat bots, which will then be able to learn to communicate with us in whatever form is most efficient rather than using English. It may be the case than pure artificial intelligence is easier to achieve than programming a convincing chat bot using the methods we are using right now.
If human imitation is what is being sought, than perhaps it would be more practical to imitate something simpler than conversation. An example would be playing a game. Any video game player can vouch for the differences between playing against a computer and playing against another player. Even simple path finding can give away that you are playing against a computer rather than a real human, or even the ability to adapt to strategies used by the player rather than having a fixed exploitable pattern.
But even this is limiting the expression of intelligence, which the computer would ideally be free to express its intelligence in any way. So then how can intelligence be measured without being limited by a particular expression? Intelligence is the ability to discover patterns which can be used to increase the probability of reaching a goal. The process of discovery is usually called "learning". If we are to accept this definition, then I shall make a case against the Turing Test by showing how a plant can be tested for intelligence.
I have lately been dabbling in some indoor gardening by placing a potato in a pot and watering it. Let's illustrate this in a picture:
I have noticed that if you place a light source to one side of the plant, after some time the plant will bend itself to face the light, like so:
And if the light is then moved, the plant will bend appropriately:
This seems like pretty nifty behaviour, but it is not intelligence for it is only responding to a fixed stimulus, in other words, there are no patterns being taken advantage of. But now suppose that we set a revolving light that orbits around the plant which goes around slowly enough for the plant to bend towards it synchronously with the light revolutions. In the absence of intelligence, the plant will simply keep on bending towards the light forever, but what if we come back to check on the plant a few months later and find this:
The plant, rather than bending towards the light, responds to the pattern of the revolving light by adapting itself so that there are leaves at every side of the plant so that at any point in time, there are some of the leaves which are facing the light. Should we ignore biological details on whether or not the extra leaves do more good than harm (maybe the leaves take less energy to maintain than the constant bending), this would be evidence that the plant is intelligent.
Now, if even a plant can be considered intelligent, which is as far away from holding a conversation with a human as an organism can be (I think), think of how unfair the Turing Test is on computers, which requires them to master the human language so much that it fools people into thinking that it is a human. Alan Turing came up with a test for human imitation, and the Turing Test is a perfect test for this, but to claim that this is the best test of intelligence is silly.
I will intentionally not propose a specific test myself, because a specific test would be quantitative and formal in nature, and intelligence is not that. Intelligence can be surprising and we should accept it as that. I would much rather take a qualitative approach to intelligence, where someone proposes a pattern that is being learnt by a computer and researchers investigate its validity.