[interestevent-interface.tentative.html]
  [source is readonly defaulting to null]
    expected: FAIL

  [InterestEventInit properties set value (manual event)]
    expected: FAIL

  [InterestEventInit properties set value (beforetoggle event)]
    expected: FAIL

  [InterestEventInit properties set value (toggle event)]
    expected: FAIL

  [source set to undefined]
    expected: FAIL

  [source set to null]
    expected: FAIL

  [source set to false]
    expected: FAIL

  [source set to true]
    expected: FAIL

  [source set to {}]
    expected: FAIL

  [source set to non-Element EventTarget]
    expected: FAIL
