'HttpResponseBase.setdefault() should not change an existing header
and should be case insensitive.'

def test_setdefault(self):

    r = HttpResponseBase()
    r['Header'] = 'Value'
    r.setdefault('header', 'changed')
    self.assertEqual(r['header'], 'Value')
    r.setdefault('x-header', 'DefaultValue')
    self.assertEqual(r['X-Header'], 'DefaultValue')
