Test messages are managed on contract level upon contract creation, the number of allowed test frames can vary between 0 and 10. Test frames have a 6 month validity period.
"Test message" is a false friend, a more accurate name would be "test message".
When using test messages, downlink is allowed. A full uplink + downlink sequence consumes two test messages.
A test message is a standard message from a device point of view : it has the same structure, bears a sequence number, etc... The difference between a test message and a standard message stands in the fact that a message considered as a test message will not trigger device activation.