events: add conversion tests

Other: How do you know these event conversions work?
Steve: Well, they've been tested and benchmarked, of course!
Other: Where are the tests?
Steve: It's easy, just check out the branch you want to test on my
       machine and the tests are right there. So easy!
Other: <facepalm>

Signed-off-by: Stephen J Day <stephen.day@docker.com>

events/convert_test.go

@@ -0,0 +1,62 @@
+package events
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	events "github.com/containerd/containerd/api/services/events/v1"
+)
+
+func TestMarshalEvent(t *testing.T) {
+	for _, testcase := range []struct {
+		event Event
+		url   string
+	}{
+		{
+			event: &events.TaskStart{},
+			url:   "types.containerd.io/containerd.services.events.v1.TaskStart",
+		},
+
+		{
+			event: &events.NamespaceUpdate{},
+			url:   "types.containerd.io/containerd.services.events.v1.NamespaceUpdate",
+		},
+	} {
+		t.Run(fmt.Sprintf("%T", testcase.event), func(t *testing.T) {
+			a, err := MarshalEvent(testcase.event)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if a.TypeUrl != testcase.url {
+				t.Fatalf("unexpected url: %v != %v", a.TypeUrl, testcase.url)
+			}
+
+			var de DynamicEvent
+			if err := UnmarshalEvent(a, &de); err != nil {
+				t.Fatal(err)
+			}
+
+			if !reflect.DeepEqual(de.Event, testcase.event) {
+				t.Fatalf("round trip failed %v != %v", de.Event, testcase.event)
+			}
+		})
+	}
+}
+
+func BenchmarkMarshalEvent(b *testing.B) {
+	ev := &events.TaskStart{}
+	expected, err := MarshalEvent(ev)
+	if err != nil {
+		b.Fatal(err)
+	}
+	for i := 0; i < b.N; i++ {
+		a, err := MarshalEvent(ev)
+		if err != nil {
+			b.Fatal(err)
+		}
+		if a.TypeUrl != expected.TypeUrl {
+			b.Fatalf("incorrect type url: %v != %v", a, expected)
+		}
+	}
+}