Usecase: UC describes that how a user use a functionality 
in the system.
Testcase: TC  describes how to test a specific 
functionality in the system.

use case describes the functionality in terms of 
input,process and domain
whereas  test case depends on usecase and defines a test 
condition to be applied

use cas describes User actions and system response

Test case contains user actions and test data,we dont know 
system response

Usecases are in business terms usecases are for capturing 
the functionality.Testcases are derived from the usecases.

Use case is the high leve scenario to test cases. use cases 
are written to tell what the user can do with the system 
and test cases are written to tell what the tester can  do 
with the system

Use case is nothing but graphical representation. That is 
prepared by based on test plan by looking at these use case 
we can easy identified whereth problems occurs

It describes how the user uses the funcnality of the system.

Test case contains user actions and test data. It is 
document that describes the action to be performed actual 
result and expected result. 
 A combination of test vairabiales is called test case.

Usecase is more elaborative than  a test case.

Usecase describes the a unique condition in order to 
validate a functionality.
A testcase describes how to execute the usecase (which 
includes test inputs,executable steps and some pre 
requisites)