Test Case Libraries
Test case libraries help to manage the reuse of test steps between test cases. When editing a test case, the test case libraries are displayed on the right side of the editor. The library contains test cases from trackers that are marked by the user as test case libraries.
1. In the Document View for Trackers, click the Open icon on the Tool Bar.
2. This opens a panel on the right side of the editor. You can view a list of different entities such as Projects, Templates, Work items, Config items and so on for the selected tracker.
3. To configure additional entities, click the Requirement Library Configuration gear icon.
4. Alternatively, you can also drag and drop steps to the left for reuse
Reusable Test Cases
Reusable test cases improve reusability and maintainability and can further reduce redundancy between test cases in projects. There is no limit to the number of reusable test cases.. The Reusable field in test cases distinguishes the reusable test cases from non-reusable test cases. To mark a test case as being reusable, select Reusable.
When editing a test case, you can filter for reusable test cases by selecting the Reusable only checkbox. You can search for and filter items by entering any text to the filter text box above the tree. The 
pointing down-right indicates that a test case is reused
pointing down-right indicates that a test case is reused