Fix: Calling dynamodb:UpdateItem with non-existent table name should raise ResourceNotFoundException

moto/dynamodb2/responses.py

@@ -947,7 +947,13 @@ class DynamoHandler(BaseResponse):
                 "Can not use both expression and non-expression parameters in the same request: Non-expression parameters: {AttributeUpdates} Expression parameters: {UpdateExpression}",
             )
         # We need to copy the item in order to avoid it being modified by the update_item operation
-        existing_item = copy.deepcopy(self.dynamodb_backend.get_item(name, key))
+        try:
+            existing_item = copy.deepcopy(self.dynamodb_backend.get_item(name, key))
+        except ValueError:
+            return self.error(
+                "com.amazonaws.dynamodb.v20111205#ResourceNotFoundException",
+                "Requested resource not found",
+            )
         if existing_item:
             existing_attributes = existing_item.to_json()["Attributes"]
         else:

tests/test_dynamodb2/exceptions/test_dynamodb_exceptions.py

@@ -534,3 +534,18 @@ def test_transact_write_items__too_many_transactions():
     err = exc.value.response["Error"]
     err["Code"].should.equal("ValidationException")
     err["Message"].should.match("Member must have length less than or equal to 25")
+
+
+@mock_dynamodb2
+def test_update_item_non_existent_table():
+    client = boto3.client("dynamodb", region_name="us-west-2")
+    with pytest.raises(client.exceptions.ResourceNotFoundException) as exc:
+        client.update_item(
+            TableName="non-existent",
+            Key={"forum_name": {"S": "LOLCat Forum"}},
+            UpdateExpression="set Body=:Body",
+            ExpressionAttributeValues={":Body": {"S": ""}},
+        )
+    err = exc.value.response["Error"]
+    assert err["Code"].should.equal("ResourceNotFoundException")
+    assert err["Message"].should.equal("Requested resource not found")