adding json decoding runtime error handling (#561)

Author: ammokhov

src/rpdk/core/contract/resource_client.py

@@ -432,9 +432,17 @@ def _call(self, payload):
         result = self._client.invoke(
             FunctionName=self._function_name, Payload=payload.encode("utf-8")
         )
-        payload = json.load(result["Payload"])
-        LOG.debug("Received response\n%s", payload)
-        return payload
+
+        try:
+            payload = json.load(result["Payload"])
+        except json.decoder.JSONDecodeError as json_error:
+            LOG.debug("Received invalid response\n%s", result["Payload"])
+            raise ValueError(
+                "Handler Output is not a valid JSON document"
+            ) from json_error
+        else:
+            LOG.debug("Received response\n%s", payload)
+            return payload
 
     def call_and_assert(
         self, action, assert_status, current_model, previous_model=None, **kwargs

tests/contract/test_resource_client.py

@@ -614,6 +614,16 @@ def test_call_and_assert_success(resource_client):
     assert error_code is None
 
 
+def test_call_and_assert_failed_invalid_payload(resource_client):
+    mock_client = resource_client._client
+    mock_client.invoke.return_value = {"Payload": StringIO("invalid json document")}
+
+    with pytest.raises(ValueError):
+        status, response, error_code = resource_client.call_and_assert(
+            Action.CREATE, OperationStatus.SUCCESS, {}, None
+        )
+
+
 def test_call_and_assert_failed(resource_client):
     mock_client = resource_client._client
     mock_client.invoke.return_value = {