'Make sure it works and clears the internal cache.
crash_id should get cleared, while product, category, and useragent
should remain.'

def test_clear_mutable_metadata(self):

    q = self.question
    q.add_metadata(product='desktop', category='fix-problems', useragent='Fyerfocks', crash_id='7')
    q.metadata
    q.clear_mutable_metadata()
    md = q.metadata
    assert ('crash_id' not in md), "clear_mutable_metadata()    didn't    clear    the    cached    metadata."
    eq_(dict(product='desktop', category='fix-problems', useragent='Fyerfocks'), md)
