Envision a scenario where a unit has passed all Unit Tests but is still exhibiting unexpected behavior when integrated into the full software system. What might be occurring, and how could this issue be diagnosed and resolved?

If a unit passes all unit tests but exhibits unexpected behavior in the integrated system, it's likely due to the unit interacting with other units differently in the integrated environment. To diagnose and resolve the issue, comprehensive integration testing should be conducted to identify the discrepancies in behavior and rectify them.