To set Case records with the same Subject (e.g. Test Case) to Closed status using Mass Update feature:
1. Navigate to Lists > Mass Update > Mass Updates.
2. On the Action column, expand Customer Support and Service and select Change Case
3. Under Criteria tab, add the necessary filters. In the case where the Support Cases have the same Subject, you may choose:
Subject = Is: Test Case or Subject = Contains: Test
4. Under Change Status To field, select Closed.
5. Click Preview to see all the cases that will be updated to Closed status.
6. Once confirmed that results are correct, click Perform Update.
For additional information refer to Help topic Making Mass Changes or Updates (ID: 8429).