func (s *DiscoverySuite) TestWatch(c *check.C) {
	d := &Discovery{}
	d.Initialize("1.1.1.1:1111,2.2.2.2:2222", 0, 0, nil)
	expected := discovery.Entries{
		&discovery.Entry{Host: "1.1.1.1", Port: "1111"},
		&discovery.Entry{Host: "2.2.2.2", Port: "2222"},
	}
	ch, _ := d.Watch(nil)
	c.Assert(expected.Equals(<-ch), check.Equals, true)
}

func TestWatch(t *testing.T) {
	d := &Discovery{}
	d.Initialize("1.1.1.1:1111,2.2.2.2:2222", 0, 0)
	expected := discovery.Entries{
		&discovery.Entry{Host: "1.1.1.1", Port: "1111"},
		&discovery.Entry{Host: "2.2.2.2", Port: "2222"},
	}
	ch, _ := d.Watch(nil)
	assert.True(t, expected.Equals(<-ch))
}

// Entries are Docker Engines
func (c *Cluster) monitorDiscovery(ch <-chan discovery.Entries, errCh <-chan error) {
	// Watch changes on the discovery channel.
	currentEntries := discovery.Entries{}
	for {
		select {
		case entries := <-ch:
			added, removed := currentEntries.Diff(entries)
			currentEntries = entries

			// Remove engines first. `addEngine` will refuse to add an engine
			// if there's already an engine with the same ID.  If an engine
			// changes address, we have to first remove it then add it back.
			for _, entry := range removed {
				c.removeEngine(entry.String())
			}

			for _, entry := range added {
				c.addEngine(entry.String())
			}
		case err := <-errCh:
			log.Errorf("Discovery error: %v", err)
		}
	}
}