There are two main pretexts that would resulting in a Chinese invasion.
1) Declaration of Independence by Taiwan
2) The discovery of nuclear arms on Taiwanese soil.
Since China has not made its move, this could mean that Taiwan does not have a program or it is being kept very secret.
"Since China has not made its move, this could mean that Taiwan does not have a program or it is being kept very secret."
I agree. If China was even remotely sure Taiwan was about to gain nuclear capability, they'd strike. But if Taiwan has a secret program and manages to develop & deploy nuclear warheads before China finds out, then the chances of war drop dramatically in the short term. China isn't about to risk having it's economic heart reduced to radioactive ashes unless they are pretty sure they can locate and strike the missiles before they can be launched.