I am using VSTS to maintain our test cases.
I have created a test suite named Login Tests inside test plan foundation, which contains all the scenarios for login validation.
I want to add all existing test cases which are in Login Tests to my new test plan. Currently, I am manually copying and pasting the IDs in the search query,but is there any way where I can get all the test cases inside a suite.
No, there is no way to do as you describe.
However there is an easy workflow change that will allow you to do this. You have some manual work to get there, but once there things will be better. You should go through all of your Test Cases in the manual Suite and tag them with "tests-login".
Once done you can easily create Query Based suites anywhere with the correct list and control the list using the Tag.
