'L{Headers.copy} creates a new independent copy of an existing
L{Headers} instance, allowing future modifications without impacts
between the copies.'

def test_copy(self):

    h = Headers()
    h.setRawHeaders('test', ['foo'])
    i = h.copy()
    self.assertEqual(i.getRawHeaders('test'), ['foo'])
    h.addRawHeader('test', 'bar')
    self.assertEqual(i.getRawHeaders('test'), ['foo'])
    i.addRawHeader('test', 'baz')
    self.assertEqual(h.getRawHeaders('test'), ['foo', 'bar'])
