I am inside the IDE and I can run all the unit tests in a file but is there any way to run all test in a project or solution at once?
If you learn executing menu commands with Alt-Letters, you can execute many commands fast even if they don't have direct shortcuts. Especially, if shortcuts are two-key combos.
As for running all tests in solution the command is Alt-RUN, i.e. Alt-R for ReSharper menu, U for Unit Testing, and N for all tests in solution.