diff --git a/mqtttest/mqtttest.go b/mqtttest/mqtttest.go
new file mode 100644
index 0000000..c2f003c
--- /dev/null
+++ b/mqtttest/mqtttest.go
@@ -0,0 +1,104 @@
+// Package mqtttest provides utilities for MQTT testing.
+package mqtttest
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/pascaldekloe/mqtt"
+)
+
+// Transfer defines a message exchange.
+type Transfer struct {
+	Message []byte // payload
+	Topic   string // destination
+	Err     error  // result
+}
+
+// PublishMock returns a new mock for mqtt.Client Publish, which compares the
+// invocation with want in order of appearance.
+func PublishMock(t *testing.T, want ...Transfer) func(message []byte, topic string) error {
+	var i int
+
+	t.Cleanup(func() {
+		if n := len(want) - i; n > 0 {
+			t.Errorf("want %d more MQTT publishes", n)
+		}
+	})
+
+	return func(message []byte, topic string) error {
+		if i >= len(want) {
+			t.Errorf("unwanted MQTT publish of %#x to %q", message, topic)
+			return nil
+		}
+		transfer := want[i]
+		i++
+
+		if !bytes.Equal(message, transfer.Message) && topic != transfer.Topic {
+			t.Errorf("got MQTT publish of %#x to %q, want %#x to %q", message, topic, transfer.Message, transfer.Topic)
+		}
+		return transfer.Err
+	}
+}
+
+// Filter defines a (un)subscription exchange.
+type Filter struct {
+	Topics []string // order is ignored
+	Err    error    // result
+}
+
+// SubscribeMock returns a new mock for mqtt.Client Subscribe,
+// SubscribeLimitAtMostOnce and SubscribeLimitAtLeastOnce, which compares the
+// invocation with want in order of appearece.
+func SubscribeMock(t *testing.T, want ...Filter) func(quit <-chan struct{}, topicFilters ...string) error {
+	var i int
+
+	t.Cleanup(func() {
+		if i < len(want) {
+			t.Errorf("want %d more MQTT subscribes", len(want)-i)
+		}
+	})
+
+	return func(quit <-chan struct{}, topicFilters ...string) error {
+		if len(topicFilters) == 0 {
+			t.Fatal("MQTT subscribe without topic filters")
+		}
+		select {
+		case <-quit:
+			return mqtt.ErrCanceled
+		default:
+			break
+		}
+
+		if i >= len(want) {
+			t.Errorf("unwanted MQTT subscribe of %q", topicFilters)
+		}
+		filter := want[i]
+		i++
+
+		todo := make(map[string]struct{}, len(filter.Topics))
+		for _, topic := range filter.Topics {
+			todo[topic] = struct{}{}
+		}
+		var wrong []string
+		for _, filter := range topicFilters {
+			if _, ok := todo[filter]; ok {
+				delete(todo, filter)
+			} else {
+				wrong = append(wrong, filter)
+			}
+		}
+		if len(wrong) != 0 {
+			t.Errorf("unwanted MQTT subscribe of %q (out of %q)", wrong, filter.Topics)
+		}
+		if len(todo) != 0 {
+			var miss []string
+			for filter := range todo {
+				miss = append(miss, filter)
+			}
+			t.Errorf("no MQTT subscribe of %q (out of %q)", miss, filter.Topics)
+		}
+
+		return filter.Err
+	}
+}