diff --git a/common/testutil/tarfile.go b/common/testutil/tarfile.go
new file mode 100644
index 00000000..08b796f5
--- /dev/null
+++ b/common/testutil/tarfile.go
@@ -0,0 +1,95 @@
+package testutil
+
+import (
+	"archive/tar"
+	"bytes"
+	"crypto/rand"
+	"fmt"
+	"io"
+	"io/ioutil"
+	mrand "math/rand"
+	"time"
+
+	"github.com/docker/docker/pkg/tarsum"
+)
+
+// CreateRandomTarFile creates a random tarfile, returning it as an
+// io.ReadSeeker along with its tarsum. An error is returned if there is a
+// problem generating valid content.
+func CreateRandomTarFile() (rs io.ReadSeeker, tarSum string, err error) {
+	nFiles := mrand.Intn(10) + 10
+	target := &bytes.Buffer{}
+	wr := tar.NewWriter(target)
+
+	// Perturb this on each iteration of the loop below.
+	header := &tar.Header{
+		Mode:       0644,
+		ModTime:    time.Now(),
+		Typeflag:   tar.TypeReg,
+		Uname:      "randocalrissian",
+		Gname:      "cloudcity",
+		AccessTime: time.Now(),
+		ChangeTime: time.Now(),
+	}
+
+	for fileNumber := 0; fileNumber < nFiles; fileNumber++ {
+		fileSize := mrand.Int63n(1<<20) + 1<<20
+
+		header.Name = fmt.Sprint(fileNumber)
+		header.Size = fileSize
+
+		if err := wr.WriteHeader(header); err != nil {
+			return nil, "", err
+		}
+
+		randomData := make([]byte, fileSize)
+
+		// Fill up the buffer with some random data.
+		n, err := rand.Read(randomData)
+
+		if n != len(randomData) {
+			return nil, "", fmt.Errorf("short read creating random reader: %v bytes != %v bytes", n, len(randomData))
+		}
+
+		if err != nil {
+			return nil, "", err
+		}
+
+		nn, err := io.Copy(wr, bytes.NewReader(randomData))
+		if nn != fileSize {
+			return nil, "", fmt.Errorf("short copy writing random file to tar")
+		}
+
+		if err != nil {
+			return nil, "", err
+		}
+
+		if err := wr.Flush(); err != nil {
+			return nil, "", err
+		}
+	}
+
+	if err := wr.Close(); err != nil {
+		return nil, "", err
+	}
+
+	reader := bytes.NewReader(target.Bytes())
+
+	// A tar builder that supports tarsum inline calculation would be awesome
+	// here.
+	ts, err := tarsum.NewTarSum(reader, true, tarsum.Version1)
+	if err != nil {
+		return nil, "", err
+	}
+
+	nn, err := io.Copy(ioutil.Discard, ts)
+	if nn != int64(len(target.Bytes())) {
+		return nil, "", fmt.Errorf("short copy when getting tarsum of random layer: %v != %v", nn, len(target.Bytes()))
+	}
+
+	if err != nil {
+		return nil, "", err
+	}
+
+	return bytes.NewReader(target.Bytes()), ts.Sum(nil), nil
+}