The missing of ForzenArray isn't technically required to make the test, however, bug 1363870 is the actual blocker here. The tests test to return the same object, however we don't support [Cache] for static interface attributes yet.
Bug 1581701 Comment 2 Edit History
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The missing of ForzenArray isn't technically required to make the test pass, however, bug 1363870 is the actual blocker here. The tests test to return the same object, however we don't support [Cache] for static interface attributes yet.