xfail backends that can't handle pending raw txns

eth_tester/utils/backend_testing.py

@@ -264,6 +264,9 @@ def test_mine_multiple_blocks(self, eth_tester):
     #
     @pytest.mark.parametrize('is_pending', [True, False])
     def test_send_raw_transaction_valid_raw_transaction(self, eth_tester, is_pending):
+        if is_pending and not hasattr(eth_tester.backend, 'send_signed_transaction'):
+            pytest.xfail("backend does not support presigned pending transactions")
+
         # send funds to our sender
         raw_privkey = b'\x11' * 32
         test_key = keys.PrivateKey(raw_privkey)

pytest.ini

@@ -1,3 +1,4 @@
 [pytest]
 addopts= -v --showlocals
 python_paths= .
+xfail_strict=True