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2. From the View Issue page for a given test
While viewing a test, navigate to the Test Executions section and when you mouse-over (or click on) a test status, you get a drop-down menu of all the test statuses. Selecting one and clicking away will immediately change the status of that test execution.
Note that if you want to provide detailed test execution information, you will have to click on the "E" button and execute as you normally do.