diff --git a/finder/fs/Android.bp b/finder/fs/Android.bp
index 27e3c7d..835eb0b 100644
--- a/finder/fs/Android.bp
+++ b/finder/fs/Android.bp
@@ -22,6 +22,7 @@
     srcs: [
         "fs.go",
         "readdir.go",
+        "test.go",
     ],
     testSrcs: [
         "readdir_test.go",
diff --git a/finder/fs/test.go b/finder/fs/test.go
new file mode 100644
index 0000000..cb2140e
--- /dev/null
+++ b/finder/fs/test.go
@@ -0,0 +1,146 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// 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 fs
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"testing"
+	"time"
+)
+
+func Write(t *testing.T, path string, content string, filesystem *MockFs) {
+	parent := filepath.Dir(path)
+	filesystem.MkDirs(parent)
+	err := filesystem.WriteFile(path, []byte(content), 0777)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func Create(t *testing.T, path string, filesystem *MockFs) {
+	Write(t, path, "hi", filesystem)
+}
+
+func Delete(t *testing.T, path string, filesystem *MockFs) {
+	err := filesystem.Remove(path)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func RemoveAll(t *testing.T, path string, filesystem *MockFs) {
+	err := filesystem.RemoveAll(path)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func Move(t *testing.T, oldPath string, newPath string, filesystem *MockFs) {
+	err := filesystem.Rename(oldPath, newPath)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func Link(t *testing.T, newPath string, oldPath string, filesystem *MockFs) {
+	parentPath := filepath.Dir(newPath)
+	err := filesystem.MkDirs(parentPath)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+	err = filesystem.Symlink(oldPath, newPath)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func Read(t *testing.T, path string, filesystem *MockFs) string {
+	reader, err := filesystem.Open(path)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	bytes, err := ioutil.ReadAll(reader)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+	return string(bytes)
+}
+
+func ModTime(t *testing.T, path string, filesystem *MockFs) time.Time {
+	stats, err := filesystem.Lstat(path)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+	return stats.ModTime()
+}
+
+func SetReadable(t *testing.T, path string, readable bool, filesystem *MockFs) {
+	err := filesystem.SetReadable(path, readable)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func SetReadErr(t *testing.T, path string, readErr error, filesystem *MockFs) {
+	err := filesystem.SetReadErr(path, readErr)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+}
+
+func AssertSameResponse(t *testing.T, actual []string, expected []string) {
+	t.Helper()
+	sort.Strings(actual)
+	sort.Strings(expected)
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("Expected Finder to return these %v paths:\n  %v,\ninstead returned these %v paths:  %v\n",
+			len(expected), expected, len(actual), actual)
+	}
+}
+
+func AssertSameStatCalls(t *testing.T, actual []string, expected []string) {
+	t.Helper()
+	sort.Strings(actual)
+	sort.Strings(expected)
+
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("Finder made incorrect Stat calls.\n"+
+			"Actual:\n"+
+			"%v\n"+
+			"Expected:\n"+
+			"%v\n"+
+			"\n",
+			actual, expected)
+	}
+}
+
+func AssertSameReadDirCalls(t *testing.T, actual []string, expected []string) {
+	t.Helper()
+	sort.Strings(actual)
+	sort.Strings(expected)
+
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("Finder made incorrect ReadDir calls.\n"+
+			"Actual:\n"+
+			"%v\n"+
+			"Expected:\n"+
+			"%v\n"+
+			"\n",
+			actual, expected)
+	}
+}