Fix bundle deploy idempotency

When a bundle is deployed which contains an application which already
exists in the model, the CLI will skip adding the application but
libjuju will raise an error. This fixes the latter behavior.

Author: johnsca

juju/bundle.py

@@ -329,6 +329,10 @@ async def run(self, context):
         :param context: is used for any methods or properties required to
             perform a change.
         """
+        if self.application in context.model.applications:
+            log.debug('Skipping %s; already in model', self.application)
+            return self.application
+
         # resolve indirect references
         charm = context.resolve(self.charm)
         options = {}

tests/unit/test_bundle.py

@@ -166,6 +166,7 @@ async def test_run(self, event_loop):
         model = mock.Mock()
         model._deploy = base.AsyncMock(return_value=None)
         model._add_store_resources = base.AsyncMock(return_value=["resource1"])
+        model.applications = {}
 
         context = mock.Mock()
         context.resolve.return_value = "charm1"
@@ -192,6 +193,13 @@ async def test_run(self, event_loop):
                                          devices="devices",
                                          num_units="num_units")
 
+        # confirm that it's idempotent
+        model.applications = {"application": None}
+        result = await change.run(context)
+        assert result == "application"
+        model._add_store_resources.assert_called_once()
+        model._deploy.assert_called_once()
+
     @pytest.mark.asyncio
     async def test_run_local(self, event_loop):
         change = AddApplicationChange(1, [], params={"charm": "local:charm",
@@ -206,6 +214,7 @@ async def test_run_local(self, event_loop):
 
         model = mock.Mock()
         model._deploy = base.AsyncMock(return_value=None)
+        model.applications = {}
 
         context = mock.Mock()
         context.resolve.return_value = "local:charm1"