diff --git a/utils/tarsum_test.go b/utils/tarsum_test.go
new file mode 100644
index 0000000000..82aea57c69
--- /dev/null
+++ b/utils/tarsum_test.go
@@ -0,0 +1,59 @@
+package utils
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+type testLayer struct {
+	filename string
+	jsonfile string
+	gzip     bool
+	tarsum   string
+}
+
+var testLayers = []testLayer{
+	testLayer{
+		filename: "testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/layer.tar",
+		jsonfile: "testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/json",
+		tarsum:   "tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b"},
+}
+
+func TestTarSums(t *testing.T) {
+	for _, layer := range testLayers {
+		fh, err := os.Open(layer.filename)
+		if err != nil {
+			t.Errorf("failed to open %s: %s", layer.filename, err)
+			continue
+		}
+		ts := &TarSum{Reader: fh}
+		_, err = io.Copy(ioutil.Discard, ts)
+		if err != nil {
+			t.Errorf("failed to copy from %s: %s", layer.filename, err)
+			continue
+		}
+		var gotSum string
+		if len(layer.jsonfile) > 0 {
+			jfh, err := os.Open(layer.jsonfile)
+			if err != nil {
+				t.Errorf("failed to open %s: %s", layer.jsonfile, err)
+				continue
+			}
+			buf, err := ioutil.ReadAll(jfh)
+			if err != nil {
+				t.Errorf("failed to readAll %s: %s", layer.jsonfile, err)
+				continue
+			}
+			gotSum = ts.Sum(buf)
+		} else {
+			gotSum = ts.Sum(nil)
+		}
+
+		if layer.tarsum != gotSum {
+			t.Errorf("expecting [%s], but got [%s]", layer.tarsum, gotSum)
+		}
+
+	}
+}
diff --git a/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/json b/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/json
new file mode 100644
index 0000000000..0f0ba4974d
--- /dev/null
+++ b/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/json
@@ -0,0 +1 @@
+{"id":"46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457","parent":"def3f9165934325dfd027c86530b2ea49bb57a0963eb1336b3a0415ff6fd56de","created":"2014-04-07T02:45:52.610504484Z","container":"e0f07f8d72cae171a3dcc35859960e7e956e0628bce6fedc4122bf55b2c287c7","container_config":{"Hostname":"88807319f25e","Domainname":"","User":"","Memory":0,"MemorySwap":0,"CpuShares":0,"AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"PortSpecs":null,"ExposedPorts":null,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":["HOME=/","PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd":["/bin/sh","-c","sed -ri 's/^(%wheel.*)(ALL)$/\\1NOPASSWD: \\2/' /etc/sudoers"],"Image":"def3f9165934325dfd027c86530b2ea49bb57a0963eb1336b3a0415ff6fd56de","Volumes":null,"WorkingDir":"","Entrypoint":null,"NetworkDisabled":false,"OnBuild":[]},"docker_version":"0.9.1-dev","config":{"Hostname":"88807319f25e","Domainname":"","User":"","Memory":0,"MemorySwap":0,"CpuShares":0,"AttachStdin":false,"AttachStdout":false,"AttachStderr":false,"PortSpecs":null,"ExposedPorts":null,"Tty":false,"OpenStdin":false,"StdinOnce":false,"Env":["HOME=/","PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd":null,"Image":"def3f9165934325dfd027c86530b2ea49bb57a0963eb1336b3a0415ff6fd56de","Volumes":null,"WorkingDir":"","Entrypoint":null,"NetworkDisabled":false,"OnBuild":[]},"architecture":"amd64","os":"linux","Size":3425}
\ No newline at end of file
diff --git a/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/layer.tar b/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/layer.tar
new file mode 100644
index 0000000000..dfd5c204ae
Binary files /dev/null and b/utils/testdata/46af0962ab5afeb5ce6740d4d91652e69206fc991fd5328c1a94d364ad00e457/layer.tar differ