':py:obj:`X509Store.add_cert` raises :py:obj:`OpenSSL.crypto.Error` if an
attempt is made to add the same certificate to the store more than once.'

def test_add_cert_rejects_duplicate(self):

    cert = load_certificate(FILETYPE_PEM, cleartextCertificatePEM)
    store = X509Store()
    store.add_cert(cert)
    self.assertRaises(Error, store.add_cert, cert)
