If I have a test suite with multiple tests, when I try to run a single unit test, either from the context menu of the code editor, or from the JUnit view, it seems to insist
If you have many tests in more than one file, and you want to run only the tests in a particular file, you could right click that file, and select run as -> junit test. Now, if you want to run only one test, contained in a file with many tests, my guess is (I dont have eclipse installed here) that the Outline view will list all test methods for a file, and you will probably be able to right click a single test method and execute it as a JUNit test.
Hope it helps.