diff --git a/provider/mesh/peer_test.go b/provider/mesh/peer_test.go
new file mode 100644
index 00000000..7c4ec363
--- /dev/null
+++ b/provider/mesh/peer_test.go
@@ -0,0 +1,141 @@
+package mesh
+
+import (
+	"bytes"
+	"encoding/gob"
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/prometheus/common/log"
+	"github.com/weaveworks/mesh"
+)
+
+func TestNotificationInfosOnGossip(t *testing.T) {
+	var (
+		t0 = time.Now()
+		t1 = t0.Add(time.Minute)
+	)
+	cases := []struct {
+		initial map[string]notificationEntry
+		msg     map[string]notificationEntry
+		delta   map[string]notificationEntry
+		final   map[string]notificationEntry
+	}{
+		{
+			initial: map[string]notificationEntry{},
+			msg: map[string]notificationEntry{
+				"123:recv1": {true, t0},
+			},
+			delta: map[string]notificationEntry{
+				"123:recv1": {true, t0},
+			},
+			final: map[string]notificationEntry{
+				"123:recv1": {true, t0},
+			},
+		}, {
+			initial: map[string]notificationEntry{
+				"123:recv1": {true, t0},
+			},
+			msg: map[string]notificationEntry{
+				"123:recv1": {false, t1},
+			},
+			delta: map[string]notificationEntry{
+				"123:recv1": {false, t1},
+			},
+			final: map[string]notificationEntry{
+				"123:recv1": {false, t1},
+			},
+		}, {
+			initial: map[string]notificationEntry{
+				"123:recv1": {true, t1},
+			},
+			msg: map[string]notificationEntry{
+				"123:recv1": {false, t0},
+			},
+			delta: map[string]notificationEntry{},
+			final: map[string]notificationEntry{
+				"123:recv1": {true, t1},
+			},
+		},
+	}
+
+	for _, c := range cases {
+		ni := NewNotificationInfos(log.Base())
+
+		ni.st.mergeComplete(c.initial)
+		var buf bytes.Buffer
+		if err := gob.NewEncoder(&buf).Encode(c.msg); err != nil {
+			t.Fatal(err)
+		}
+		// OnGossip expects the delta but an empty set to be replaced with nil.
+		d, err := ni.OnGossip(buf.Bytes())
+		if err != nil {
+			t.Errorf("%v OnGossip %v: %s", c.initial, c.msg, err)
+			continue
+		}
+		want := c.final
+		if have := ni.st.set; !reflect.DeepEqual(want, have) {
+			t.Errorf("%v OnGossip %v: want %v, have %v", c.initial, c.msg, want, have)
+		}
+
+		want = c.delta
+		if len(c.delta) == 0 {
+			want = nil
+		}
+		if d != nil {
+			if have := d.(*notificationState).set; !reflect.DeepEqual(want, have) {
+				t.Errorf("%v OnGossip %v: want %v, have %v", c.initial, c.msg, want, have)
+			}
+		} else if want != nil {
+			t.Errorf("%v OnGossip %v: want nil", c.initial, c.msg)
+		}
+	}
+
+	for _, c := range cases {
+		ni := NewNotificationInfos(log.Base())
+
+		ni.st.mergeComplete(c.initial)
+		var buf bytes.Buffer
+		if err := gob.NewEncoder(&buf).Encode(c.msg); err != nil {
+			t.Fatal(err)
+		}
+
+		// OnGossipBroadcast expects the provided delta as is.
+		d, err := ni.OnGossipBroadcast(mesh.UnknownPeerName, buf.Bytes())
+		if err != nil {
+			t.Errorf("%v OnGossipBroadcast %v: %s", c.initial, c.msg, err)
+			continue
+		}
+		want := c.final
+		if have := ni.st.set; !reflect.DeepEqual(want, have) {
+			t.Errorf("%v OnGossip %v: want %v, have %v", c.initial, c.msg, want, have)
+		}
+
+		want = c.delta
+		if have := d.(*notificationState).set; !reflect.DeepEqual(want, have) {
+			t.Errorf("%v OnGossipBroadcast %v: want %v, have %v", c.initial, c.msg, want, have)
+		}
+	}
+
+	for _, c := range cases {
+		ni := NewNotificationInfos(log.Base())
+
+		ni.st.mergeComplete(c.initial)
+		var buf bytes.Buffer
+		if err := gob.NewEncoder(&buf).Encode(c.msg); err != nil {
+			t.Fatal(err)
+		}
+		// OnGossipUnicast always expects the full state back.
+		err := ni.OnGossipUnicast(mesh.UnknownPeerName, buf.Bytes())
+		if err != nil {
+			t.Errorf("%v OnGossip %v: %s", c.initial, c.msg, err)
+			continue
+		}
+
+		want := c.final
+		if have := ni.st.set; !reflect.DeepEqual(want, have) {
+			t.Errorf("%v OnGossip %v: want %v, have %v", c.initial, c.msg, want, have)
+		}
+	}
+}