In a VS2015 Unit Test project you are able to right click the project and add an ordered test. This enables you to order your unit tests in a file with the extension orderedtest.
I can't find the correct syntax to use with MSTest.exe to run this orderedtest file.
The test container is a file that contains the tests you want to run. For example, for ordered tests, the test container is the .orderedtest file that defines the ordered test. For unit tests, it is the assembly built from the test project that contains the unit test source files.
See Also
How to run a ordered test from MSTest command line