diff --git a/datasource/configdrive/configdrive_test.go b/datasource/configdrive/configdrive_test.go
index 5d72a19..fa42209 100644
--- a/datasource/configdrive/configdrive_test.go
+++ b/datasource/configdrive/configdrive_test.go
@@ -15,83 +15,75 @@
 package configdrive
 
 import (
-	"os"
 	"testing"
+
+	"github.com/coreos/coreos-cloudinit/datasource/test"
 )
 
-type mockFilesystem []string
-
-func (m mockFilesystem) readFile(filename string) ([]byte, error) {
-	for _, file := range m {
-		if file == filename {
-			return []byte(filename), nil
-		}
-	}
-	return nil, os.ErrNotExist
-}
-
 func TestFetchMetadata(t *testing.T) {
 	for _, tt := range []struct {
-		root     string
-		filename string
-		files    mockFilesystem
+		root  string
+		files test.MockFilesystem
+
+		metadata string
 	}{
 		{
 			"/",
+			test.MockFilesystem{},
 			"",
-			mockFilesystem{},
 		},
 		{
 			"/",
-			"/openstack/latest/meta_data.json",
-			mockFilesystem([]string{"/openstack/latest/meta_data.json"}),
+			test.MockFilesystem{"/openstack/latest/meta_data.json": "metadata"},
+			"metadata",
 		},
 		{
 			"/media/configdrive",
-			"/media/configdrive/openstack/latest/meta_data.json",
-			mockFilesystem([]string{"/media/configdrive/openstack/latest/meta_data.json"}),
+			test.MockFilesystem{"/media/configdrive/openstack/latest/meta_data.json": "metadata"},
+			"metadata",
 		},
 	} {
-		cd := configDrive{tt.root, tt.files.readFile}
-		filename, err := cd.FetchMetadata()
+		cd := configDrive{tt.root, tt.files.ReadFile}
+		metadata, err := cd.FetchMetadata()
 		if err != nil {
 			t.Fatalf("bad error for %q: want %v, got %q", tt, nil, err)
 		}
-		if string(filename) != tt.filename {
-			t.Fatalf("bad path for %q: want %q, got %q", tt, tt.filename, filename)
+		if string(metadata) != tt.metadata {
+			t.Fatalf("bad path for %q: want %q, got %q", tt, tt.metadata, metadata)
 		}
 	}
 }
 
 func TestFetchUserdata(t *testing.T) {
 	for _, tt := range []struct {
-		root     string
-		filename string
-		files    mockFilesystem
+		root  string
+		files test.MockFilesystem
+
+		userdata string
 	}{
 		{
 			"/",
+			test.MockFilesystem{},
 			"",
-			mockFilesystem{},
 		},
 		{
 			"/",
-			"/openstack/latest/user_data",
-			mockFilesystem([]string{"/openstack/latest/user_data"}),
+			test.MockFilesystem{"/openstack/latest/user_data": "userdata"},
+			"userdata",
 		},
 		{
 			"/media/configdrive",
-			"/media/configdrive/openstack/latest/user_data",
-			mockFilesystem([]string{"/media/configdrive/openstack/latest/user_data"}),
+			test.MockFilesystem{"/media/configdrive/openstack/latest/user_data": "userdata"},
+			"userdata",
 		},
 	} {
-		cd := configDrive{tt.root, tt.files.readFile}
-		filename, err := cd.FetchUserdata()
+		cd := configDrive{tt.root, tt.files.ReadFile}
+		userdata, err := cd.FetchUserdata()
 		if err != nil {
 			t.Fatalf("bad error for %q: want %v, got %q", tt, nil, err)
 		}
-		if string(filename) != tt.filename {
-			t.Fatalf("bad path for %q: want %q, got %q", tt, tt.filename, filename)
+		if string(userdata) != tt.userdata {
+			t.Fatalf("bad path for %q: want %q, got %q", tt, tt.userdata, userdata)
 		}
 	}
 }
diff --git a/datasource/test/test.go b/datasource/test/test.go
new file mode 100644
index 0000000..84696e2
--- /dev/null
+++ b/datasource/test/test.go
@@ -0,0 +1,28 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package test
+
+import (
+	"os"
+)
+
+type MockFilesystem map[string]string
+
+func (m MockFilesystem) ReadFile(filename string) ([]byte, error) {
+	if contents, ok := m[filename]; ok {
+		return []byte(contents), nil
+	}
+	return nil, os.ErrNotExist
+}
diff --git a/datasource/waagent/waagent_test.go b/datasource/waagent/waagent_test.go
index 464d551..326c6a0 100644
--- a/datasource/waagent/waagent_test.go
+++ b/datasource/waagent/waagent_test.go
@@ -16,44 +16,36 @@ package waagent
 
 import (
 	"encoding/json"
-	"os"
 	"reflect"
 	"testing"
+
+	"github.com/coreos/coreos-cloudinit/datasource/test"
 )
 
-type mockFilesystem map[string][]byte
-
-func (m mockFilesystem) readFile(filename string) ([]byte, error) {
-	if contents := m[filename]; contents != nil {
-		return contents, nil
-	}
-	return nil, os.ErrNotExist
-}
-
 func TestFetchMetadata(t *testing.T) {
 	for _, tt := range []struct {
 		root     string
-		files    mockFilesystem
+		files    test.MockFilesystem
 		metadata map[string]string
 	}{
 		{
 			"/",
-			mockFilesystem{},
+			test.MockFilesystem{},
 			nil,
 		},
 		{
 			"/",
-			mockFilesystem{"/SharedConfig.xml": []byte("")},
+			test.MockFilesystem{"/SharedConfig.xml": ""},
 			nil,
 		},
 		{
 			"/var/lib/waagent",
-			mockFilesystem{"/var/lib/waagent/SharedConfig.xml": []byte("")},
+			test.MockFilesystem{"/var/lib/waagent/SharedConfig.xml": ""},
 			nil,
 		},
 		{
 			"/var/lib/waagent",
-			mockFilesystem{"/var/lib/waagent/SharedConfig.xml": []byte(`<?xml version="1.0" encoding="utf-8"?>
+			test.MockFilesystem{"/var/lib/waagent/SharedConfig.xml": `<?xml version="1.0" encoding="utf-8"?>
 <SharedConfig version="1.0.0.0" goalStateIncarnation="1">
   <Deployment name="c8f9e4c9c18948e1bebf57c5685da756" guid="{1d10394f-c741-4a1a-a6bb-278f213c5a5e}" incarnation="0" isNonCancellableTopologyChangeEnabled="false">
     <Service name="core-test-1" guid="{00000000-0000-0000-0000-000000000000}" />
@@ -89,14 +81,14 @@ func TestFetchMetadata(t *testing.T) {
       </InputEndpoints>
     </Instance>
   </Instances>
-</SharedConfig>`)},
+</SharedConfig>`},
 			map[string]string{
 				"local-ipv4":  "100.73.202.64",
 				"public-ipv4": "191.239.39.77",
 			},
 		},
 	} {
-		a := waagent{tt.root, tt.files.readFile}
+		a := waagent{tt.root, tt.files.ReadFile}
 		metadataBytes, err := a.FetchMetadata()
 		if err != nil {
 			t.Fatalf("bad error for %q: want %v, got %q", tt, nil, err)
@@ -116,22 +108,22 @@ func TestFetchMetadata(t *testing.T) {
 func TestFetchUserdata(t *testing.T) {
 	for _, tt := range []struct {
 		root  string
-		files mockFilesystem
+		files test.MockFilesystem
 	}{
 		{
 			"/",
-			mockFilesystem{},
+			test.MockFilesystem{},
 		},
 		{
 			"/",
-			mockFilesystem{"/CustomData": []byte{}},
+			test.MockFilesystem{"/CustomData": ""},
 		},
 		{
 			"/var/lib/waagent/",
-			mockFilesystem{"/var/lib/waagent/CustomData": []byte{}},
+			test.MockFilesystem{"/var/lib/waagent/CustomData": ""},
 		},
 	} {
-		a := waagent{tt.root, tt.files.readFile}
+		a := waagent{tt.root, tt.files.ReadFile}
 		_, err := a.FetchUserdata()
 		if err != nil {
 			t.Fatalf("bad error for %q: want %v, got %q", tt, nil, err)