test(message): test custom CID type (#309)

This got dropped from my other patch.

message/pb/cid_test.go

+package bitswap_message_pb_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ipfs/go-cid"
+	u "github.com/ipfs/go-ipfs-util"
+
+	pb "github.com/ipfs/go-bitswap/message/pb"
+)
+
+func TestCID(t *testing.T) {
+	var expected = [...]byte{
+		10, 34, 18, 32, 195, 171,
+		143, 241, 55, 32, 232, 173,
+		144, 71, 221, 57, 70, 107,
+		60, 137, 116, 229, 146, 194,
+		250, 56, 61, 74, 57, 96,
+		113, 76, 174, 240, 196, 242,
+	}
+
+	c := cid.NewCidV0(u.Hash([]byte("foobar")))
+	msg := pb.Message_BlockPresence{Cid: pb.Cid{Cid: c}}
+	actual, err := msg.Marshal()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(actual, expected[:]) {
+		t.Fatal("failed to correctly encode custom CID type")
+	}
+}