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?
I'm surprised no one mentioned it here, but pretty much all resharper commands can be assigned to specific custom keyboard shortcuts. Go to Tools --> Options --> Keyboard, and find the command you're interested (just type "resharper" in the "show commands containing" text field & you'll find them all). In this specific instance, the "Run All Tests from Solution" command is "ReSharper.UnitTest_RunSolution".
In ReSharper 9.x, the command name is ReSharper.ReSharper_UnitTestRunSolution.