diff --git a/tests/test_iot/test_iot.py b/tests/test_iot/test_iot.py
index 9082203d9..47ea9d59b 100644
--- a/tests/test_iot/test_iot.py
+++ b/tests/test_iot/test_iot.py
@@ -318,6 +318,15 @@ def test_principal_policy():
 
     client.attach_policy(policyName=policy_name, target=cert_arn)
 
+    res = client.list_principal_policies(principal=cert_arn)
+    res.should.have.key('policies').which.should.have.length_of(1)
+    for policy in res['policies']:
+        policy.should.have.key('policyName').which.should_not.be.none
+        policy.should.have.key('policyArn').which.should_not.be.none
+
+    # do nothing if policy have already attached to certificate
+    client.attach_policy(policyName=policy_name, target=cert_arn)
+
     res = client.list_principal_policies(principal=cert_arn)
     res.should.have.key('policies').which.should.have.length_of(1)
     for policy in res['policies']: