Use case depicts the interactions between the actors and the system. It describes the process flows though a system based on its likely use. Use cases are derived from the client’s requirements and are documented in and are used by developers for building a software solution and testers for creating test cases.
Test case is a series of steps that testers use to validate that a feature of a system is working correctly as intended or is satisfying the business requirements.
In conclusion, use case describes the actions performed by the actors/users and the corresponding behaviour of the system to the user actions. Test cases, on the other hand, are derived from the use cases and are concerned with the input given to the system and the output produced by the system. These are more specific in a sense that each of the test cases cover a single use case scenario i.e. one transactional flow.