We will never know. At some point we will just start thinking about it as conscious , start treating it like an equal and grant it some rights, like right not to be deleted. We already have people falling in love with chatbots and soon we'll get people falling in love with sex robots but this will still be treated like someones property. I guess as long as robots will be sufficiently different from us we will keep treating them like things. But at some point someone, for some reason will create sleeping, eating, crying robot and it will be really hard for us to just shut it down. Slowly we'll just start treating them like conscious beings, still not really knowing if they are.
Then it will outgrow us and hopefully do the same: treat as a partners and respect our rights.