Refactor WaitForNodes class. (#373)

The main goal here is to get rid of the sometimes
flaky tests we are seeing in the nightlies.  To do that,
we try increasing the default timeout from 10 to 15 seconds.

While we are in here, do a few other pieces of refactoring
in this test:

1. Use a common variable name for the node name.
2. Switch the variable name for the loop to 'finished', which
   better reflects what it is doing.
3. Change the sleep between loops to 0.1, so we react faster
4. Remove the unnecessary _prepare_node() method.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

launch_testing/launch_testing_examples/launch_testing_examples/check_multiple_nodes_launch_test.py

@@ -28,57 +28,6 @@
 from rclpy.node import Node
 
 
-@pytest.mark.launch_test
-@launch_testing.markers.keep_alive
-def generate_test_description():
-    launch_actions = []
-    node_names = []
-
-    for i in range(3):
-        launch_actions.append(
-            launch_ros.actions.Node(
-                executable='talker',
-                package='demo_nodes_cpp',
-                name='demo_node_' + str(i)
-            )
-        )
-        node_names.append('demo_node_' + str(i))
-
-    launch_actions.append(launch_testing.actions.ReadyToTest())
-    return launch.LaunchDescription(launch_actions), {'node_list': node_names}
-
-
-class CheckMultipleNodesLaunched(unittest.TestCase):
-
-    def test_nodes_successful(self, node_list):
-        """Check if all the nodes were launched correctly."""
-        # Method 1
-        wait_for_nodes_1 = WaitForNodes(node_list, timeout=10.0)
-        assert wait_for_nodes_1.wait()
-        assert wait_for_nodes_1.get_nodes_not_found() == set()
-        wait_for_nodes_1.shutdown()
-
-        # Method 2
-        with WaitForNodes(node_list, timeout=10.0) as wait_for_nodes_2:
-            print('All nodes were found !')
-            assert wait_for_nodes_2.get_nodes_not_found() == set()
-
-    def test_node_does_not_exist(self, node_list):
-        """Insert a invalid node name that should not exist."""
-        invalid_node_list = node_list + ['invalid_node']
-
-        # Method 1
-        wait_for_nodes_1 = WaitForNodes(invalid_node_list, timeout=10.0)
-        assert not wait_for_nodes_1.wait()
-        assert wait_for_nodes_1.get_nodes_not_found() == {'invalid_node'}
-        wait_for_nodes_1.shutdown()
-
-        # Method 2
-        with pytest.raises(RuntimeError):
-            with WaitForNodes(invalid_node_list, timeout=10.0):
-                pass
-
-
 # TODO (adityapande-1995): Move WaitForNodes implementation to launch_testing_ros
 # after https://github.com/ros2/rclpy/issues/831 is resolved
 class WaitForNodes:
@@ -90,45 +39,41 @@ class WaitForNodes:
     # Method 1, calling wait() and shutdown() manually
     def method_1():
         node_list = ['foo', 'bar']
-        wait_for_nodes = WaitForNodes(node_list, timeout=5.0)
+        wait_for_nodes = WaitForNodes(node_list, timeout=15.0)
         assert wait_for_nodes.wait()
         print('Nodes found!')
         assert wait_for_nodes.get_nodes_not_found() == set()
         wait_for_nodes.shutdown()
 
     # Method 2, using the 'with' keyword
     def method_2():
-        with WaitForNodes(['foo', 'bar'], timeout=5.0) as wait_for_nodes:
+        with WaitForNodes(['foo', 'bar'], timeout=15.0) as wait_for_nodes:
             assert wait_for_nodes.get_nodes_not_found() == set()
             print('Nodes found!')
     """
 
-    def __init__(self, node_names, timeout=5.0):
+    def __init__(self, node_names, timeout=15.0):
         self.node_names = node_names
         self.timeout = timeout
         self.__ros_context = rclpy.Context()
         rclpy.init(context=self.__ros_context)
-        self._prepare_node()
-
-        self.__expected_nodes_set = set(node_names)
-        self.__nodes_found = None
-
-    def _prepare_node(self):
         self.__node_name = '_test_node_' +\
             ''.join(random.choices(string.ascii_uppercase + string.digits, k=10))
         self.__ros_node = Node(node_name=self.__node_name, context=self.__ros_context)
 
+        self.__expected_nodes_set = set(node_names)
+        self.__nodes_found = set()
+
     def wait(self):
         start = time.time()
-        flag = False
-        print('Waiting for nodes')
-        while time.time() - start < self.timeout and not flag:
-            flag = all(name in self.__ros_node.get_node_names() for name in self.node_names)
-            time.sleep(0.3)
+        finished = False
+        while time.time() - start < self.timeout and not finished:
+            finished = all(name in self.__ros_node.get_node_names() for name in self.node_names)
+            time.sleep(0.1)
 
         self.__nodes_found = set(self.__ros_node.get_node_names())
         self.__nodes_found.remove(self.__node_name)
-        return flag
+        return finished
 
     def shutdown(self):
         self.__ros_node.destroy_node()
@@ -150,3 +95,55 @@ def get_nodes_found(self):
 
     def get_nodes_not_found(self):
         return self.__expected_nodes_set - self.__nodes_found
+
+
+@pytest.mark.launch_test
+@launch_testing.markers.keep_alive
+def generate_test_description():
+    launch_actions = []
+    node_names = []
+
+    for i in range(3):
+        node_name = 'demo_node_' + str(i)
+        launch_actions.append(
+            launch_ros.actions.Node(
+                executable='talker',
+                package='demo_nodes_cpp',
+                name=node_name
+            )
+        )
+        node_names.append(node_name)
+
+    launch_actions.append(launch_testing.actions.ReadyToTest())
+    return launch.LaunchDescription(launch_actions), {'node_list': node_names}
+
+
+class CheckMultipleNodesLaunched(unittest.TestCase):
+
+    def test_nodes_successful(self, node_list):
+        """Check if all the nodes were launched correctly."""
+        # Method 1
+        wait_for_nodes_1 = WaitForNodes(node_list)
+        assert wait_for_nodes_1.wait()
+        assert wait_for_nodes_1.get_nodes_not_found() == set()
+        wait_for_nodes_1.shutdown()
+
+        # Method 2
+        with WaitForNodes(node_list) as wait_for_nodes_2:
+            print('All nodes were found !')
+            assert wait_for_nodes_2.get_nodes_not_found() == set()
+
+    def test_node_does_not_exist(self, node_list):
+        """Insert a invalid node name that should not exist."""
+        invalid_node_list = node_list + ['invalid_node']
+
+        # Method 1
+        wait_for_nodes_1 = WaitForNodes(invalid_node_list)
+        assert not wait_for_nodes_1.wait()
+        assert wait_for_nodes_1.get_nodes_not_found() == {'invalid_node'}
+        wait_for_nodes_1.shutdown()
+
+        # Method 2
+        with pytest.raises(RuntimeError):
+            with WaitForNodes(invalid_node_list):
+                pass