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Tests the returnValue attribute of the BeforeUnloadEvent.

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".


PASS testEvent.__proto__ is BeforeUnloadEvent.prototype
PASS testEvent.returnValue is ""
PASS testEvent.returnValue is "This is beforeunload from the top level frame."
PASS successfullyParsed is true

TEST COMPLETE