The MSTest Action takes different inputs depending on the test format type you select.
Type: Test container or assembly
When specifying containers/assemblies, you can optionally supply a comma separated list of tests (ie. test methods) which you only want to test.
Type: Test metadata
When specifying a metadata test file, you can optionally supply a comma separated list of tests (ie. test methods) and/or a comma separated list of test lists.
The follow options are common to both types.
Configuration File
This field is optional. If you supply this option it will be used over the default one.
Results File
This file is also optional. If you don't supply one, the test output location will be up to the MSTest executable.
Using
The Using drop down is populated with any property collector whose namespace matches the pattern defined by the MSTest Action. The pattern for this action is ^MSTest.*
If you create a property collector for this action, make sure you select the Path Finder PlugIn type and give it a name that will match the pattern above in blue. Example names listed here, search the table's Plugin column for "MSTest".
For more in-depth explanations on property collectors see Property Collectors.
Alternatively, you can select the Custom option from the Using drop down list and specify a path in the resulting input field that will be displayed. Please read Why it's a good idea to use a property collector before using this option.