upgrader: new WatchForEnvironConfigChanges

state/state_test.go

Index: state/state_test.go
=== modified file 'state/state_test.go'
--- state/state_test.go	2013-07-03 15:14:20 +0000
+++ state/state_test.go	2013-07-04 14:12:18 +0000
@@ -1093,6 +1093,49 @@
 	assertChange(attrs{"fancy-new-key": "arbitrary-value"})
 }
 
+// setAgentVersion sets the current agent version in the state's
+// environment configuration.
+func setAgentVersion(st *state.State, vers version.Number) error {
+	cfg, err := st.EnvironConfig()
+	if err != nil {
+		return err
+	}
+	cfg, err = cfg.Apply(map[string]interface{}{"agent-version": vers.String()})
+	if err != nil {
+		panic(fmt.Errorf("config refused agent-version: %v", err))
+	}
+	return st.SetEnvironConfig(cfg)
+}
+
+func (s *StateSuite) TestWatchForEnvironConfigChanges(c *C) {
+	cur := version.Current.Number
+	err := setAgentVersion(s.State, cur)
+	c.Assert(err, IsNil)
+	w := s.State.WatchForEnvironConfigChanges()
+	defer statetesting.AssertStop(c, w)
+
+	wc := statetesting.NewNotifyWatcherC(c, s.State, w)
+	// Initially we get one change notification
+	wc.AssertOneChange()
+
+	// Multiple changes will only result in a single change notification
+	newVersion := cur
+	newVersion.Minor += 1
+	err = setAgentVersion(s.State, newVersion)
+	c.Assert(err, IsNil)
+
+	newerVersion := newVersion
+	newerVersion.Minor += 1
+	err = setAgentVersion(s.State, newerVersion)
+	c.Assert(err, IsNil)
+	wc.AssertOneChange()
+
+	// Setting it to the same value does not trigger a change notification
+	err = setAgentVersion(s.State, newerVersion)
+	c.Assert(err, IsNil)
+	wc.AssertNoChange()
+}
+
 func (s *StateSuite) TestWatchEnvironConfigCorruptConfig(c *C) {
 	cfg, err := s.State.EnvironConfig()
 	c.Assert(err, IsNil)