The difference is very subtle. Both methods run the test and at the very core Test Studio code is called to run each step of the test. The differences are:
- Clicking Execute at the top of the test steps causes the test to be run via our own ArtOfTest.Runner utility and present results directly in the test steps UI.
- Clicking Run Selected Tests runs the test via Microsoft's MSTest utility (which in turn calls our DLL's to execute the test steps) and produces a Microsoft formatted .trx file with the results. This is also the method with which you can do true source code debugging of your coded steps.
That's about it.