answer is validation for both of them.

writing test case is a test data required to test the 
application.Test data may be input/setup/procure to test.so 
it should not be verification or validation.

executing test cases is a vaildation.since checking the 
correctness of created application /code with the test data.

writing test cases is averification and execute test 
casesis avalidation

Writing test cases is neither verification or validation as 
nothing is performed on application.However reviewing test 
cases is verification. This is to confirm that the test 
cases are built based on requirments.
Executing test cases is validation.

Let me know if I am not correct.