'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(u'test\xe1', [u'foo\u2603'])
    i = h.copy()
    self.assertEqual(i.getRawHeaders(u'test\xe1'), [u'foo\u2603'])
    self.assertEqual(i.getRawHeaders('test\xe1'), ['foo\xe2\x98\x83'])
    h.addRawHeader(u'test\xe1', u'bar')
    self.assertEqual(i.getRawHeaders(u'test\xe1'), [u'foo\u2603'])
    self.assertEqual(i.getRawHeaders('test\xe1'), ['foo\xe2\x98\x83'])
    i.addRawHeader(u'test\xe1', 'baz')
    self.assertEqual(h.getRawHeaders(u'test\xe1'), [u'foo\u2603', u'bar'])
    self.assertEqual(h.getRawHeaders('test\xe1'), ['foo\xe2\x98\x83', 'bar'])
