diff --git a/main.go b/main.go
index 700f2b6..7b2b34c 100644
--- a/main.go
+++ b/main.go
@@ -15,7 +15,6 @@ type (
 	}
 
 	cmdManifest struct{} // stub
-
 )
 
 func main() {
diff --git a/rootfs/BUILD b/rootfs/BUILD
index ca38d4e..eaef33a 100644
--- a/rootfs/BUILD
+++ b/rootfs/BUILD
@@ -2,7 +2,10 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "rootfs_lib",
-    srcs = ["rootfs.go"],
+    srcs = [
+        "rootfs.go",
+        "rootfs_tests.go",
+    ],
     importpath = "github.com/motiejus/code/undocker/rootfs",
     visibility = ["//visibility:public"],
 )
diff --git a/rootfs/rootfs.go b/rootfs/rootfs.go
index 4c3f1e8..bf99fce 100644
--- a/rootfs/rootfs.go
+++ b/rootfs/rootfs.go
@@ -26,7 +26,7 @@ type dockerManifestJSON []struct {
 //       I) layer name
 //       II) offset (0 being the first file in the layer)
 // 4. go through
-func Rootfs(in io.ReadSeeker, out io.Writer) error {
+func RootFS(in io.ReadSeeker, out io.Writer) error {
 	tr := tar.NewReader(in)
 	tw := tar.NewWriter(out)
 	// layerOffsets maps a layer name (a9b123c0daa/layer.tar) to it's offset
diff --git a/rootfs/rootfs_tests.go b/rootfs/rootfs_tests.go
new file mode 100644
index 0000000..a858792
--- /dev/null
+++ b/rootfs/rootfs_tests.go
@@ -0,0 +1,82 @@
+package rootfs
+
+import (
+	"archive/tar"
+	"bytes"
+	"encoding/json"
+	"testing"
+)
+
+type layers []string
+
+func (l layers) bytes() []byte {
+	dockerManifest := dockerManifestJSON{{Layers: l}}
+	b, err := json.Marshal(dockerManifest)
+	if err != nil {
+		panic("panic in a unit test")
+	}
+	return b
+}
+
+type tarrable interface {
+	tar(*tar.Writer)
+}
+
+type file struct {
+	name     string
+	contents []byte
+	uid      int
+}
+
+func (f file) tar(tw *tar.Writer) {
+	hdr := &tar.Header{Typeflag: tar.TypeReg, Uid: f.uid}
+	tw.WriteHeader(hdr)
+	tw.Write(f.contents)
+}
+
+type dir struct {
+	name string
+	uid  int
+}
+
+func (f dir) tar(tw *tar.Writer) {
+	hdr := &tar.Header{Typeflag: tar.TypeDir, Uid: f.uid}
+	tw.WriteHeader(hdr)
+}
+
+type tarball []tarrable
+
+func (t tarball) bytes() []byte {
+	buf := bytes.Buffer{}
+	tw := tar.NewWriter(&buf)
+	for _, member := range t {
+		member.tar(tw)
+	}
+	tw.Close()
+	return buf.Bytes()
+}
+
+var (
+	_layer0 = tarball{
+		dir{name: "/", uid: 0},
+		file{name: "/file", uid: 1, contents: []byte("from 0")},
+	}
+
+	_layer1 = tarball{
+		dir{name: "/", uid: 1},
+		file{name: "/file", uid: 0, contents: []byte("from 1")},
+	}
+
+	_image = tarball{
+		file{name: "layer1/layer.tar", contents: _layer1.bytes()},
+		file{name: "layer0/layer.tar", contents: _layer0.bytes()},
+		file{
+			name:     "manifest.json",
+			contents: layers{"layer0/layer.tar", "layer1/layer0.tar"}.bytes(),
+		},
+	}
+)
+
+func RootFSTest(t *testing.T) {
+
+}