add xmllint linter test (ros2/rosidl_python#53)

* add ament_xmllint test

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

* fix xmllint error

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

* instead of leveling the schema up level the format down since the manifest doesn't use format 3 features

Signed-off-by: Dirk Thomas <dirk-thomas@users.noreply.github.com>

package.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
-<package format="3">
+<package format="2">
   <name>rosidl_runtime_py</name>
   <version>0.7.1</version>
   <description>Runtime utilities for working with generated ROS interfaces in Python.</description>
@@ -16,6 +16,7 @@
   <test_depend>ament_copyright</test_depend>
   <test_depend>ament_flake8</test_depend>
   <test_depend>ament_pep257</test_depend>
+  <test_depend>ament_xmllint</test_depend>
   <test_depend>python3-pytest</test_depend>
   <test_depend>test_msgs</test_depend>
 

test/test_xmllint.py

@@ -0,0 +1,23 @@
+# Copyright 2019 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ament_xmllint.main import main
+import pytest
+
+
+@pytest.mark.linter
+@pytest.mark.xmllint
+def test_xmllint():
+    rc = main(argv=[])
+    assert rc == 0, 'Found errors'