diff --git a/tools/compliance/testfs/testfs.go b/tools/compliance/testfs/testfs.go
new file mode 100644
index 0000000..2c75c5b
--- /dev/null
+++ b/tools/compliance/testfs/testfs.go
@@ -0,0 +1,129 @@
+// Copyright 2022 Google LLC
+//
+// 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 testfs
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"strings"
+	"time"
+)
+
+// TestFS implements a test file system (fs.FS) simulated by a map from filename to []byte content.
+type TestFS map[string][]byte
+
+var _ fs.FS = (*TestFS)(nil)
+var _ fs.StatFS = (*TestFS)(nil)
+
+// Open implements fs.FS.Open() to open a file based on the filename.
+func (tfs *TestFS) Open(name string) (fs.File, error) {
+	if _, ok := (*tfs)[name]; !ok {
+		return nil, fmt.Errorf("unknown file %q", name)
+	}
+	return &TestFile{tfs, name, 0}, nil
+}
+
+// Stat implements fs.StatFS.Stat() to examine a file based on the filename.
+func (tfs *TestFS) Stat(name string) (fs.FileInfo, error) {
+	if content, ok := (*tfs)[name]; ok {
+		return &TestFileInfo{name, len(content), 0666}, nil
+	}
+	dirname := name
+	if !strings.HasSuffix(dirname, "/") {
+		dirname = dirname + "/"
+	}
+	for name := range (*tfs) {
+		if strings.HasPrefix(name, dirname) {
+			return &TestFileInfo{name, 8, fs.ModeDir | fs.ModePerm}, nil
+		}
+	}
+	return nil, fmt.Errorf("file not found: %q", name)
+}
+
+// TestFileInfo implements a file info (fs.FileInfo) based on TestFS above.
+type TestFileInfo struct {
+	name string
+	size int
+	mode fs.FileMode
+}
+
+var _ fs.FileInfo = (*TestFileInfo)(nil)
+
+// Name returns the name of the file
+func (fi *TestFileInfo) Name() string {
+	return fi.name
+}
+
+// Size returns the size of the file in bytes.
+func (fi *TestFileInfo) Size() int64 {
+	return int64(fi.size)
+}
+
+// Mode returns the fs.FileMode bits.
+func (fi *TestFileInfo) Mode() fs.FileMode {
+	return fi.mode
+}
+
+// ModTime fakes a modification time.
+func (fi *TestFileInfo) ModTime() time.Time {
+	return time.UnixMicro(0xb0bb)
+}
+
+// IsDir is a synonym for Mode().IsDir()
+func (fi *TestFileInfo) IsDir() bool {
+	return fi.mode.IsDir()
+}
+
+// Sys is unused and returns nil.
+func (fi *TestFileInfo) Sys() any {
+	return nil
+}
+
+// TestFile implements a test file (fs.File) based on TestFS above.
+type TestFile struct {
+	fs   *TestFS
+	name string
+	posn int
+}
+
+var _ fs.File = (*TestFile)(nil)
+
+// Stat not implemented to obviate implementing fs.FileInfo.
+func (f *TestFile) Stat() (fs.FileInfo, error) {
+	return f.fs.Stat(f.name)
+}
+
+// Read copies bytes from the TestFS map.
+func (f *TestFile) Read(b []byte) (int, error) {
+	if f.posn < 0 {
+		return 0, fmt.Errorf("file not open: %q", f.name)
+	}
+	if f.posn >= len((*f.fs)[f.name]) {
+		return 0, io.EOF
+	}
+	n := copy(b, (*f.fs)[f.name][f.posn:])
+	f.posn += n
+	return n, nil
+}
+
+// Close marks the TestFile as no longer in use.
+func (f *TestFile) Close() error {
+	if f.posn < 0 {
+		return fmt.Errorf("file already closed: %q", f.name)
+	}
+	f.posn = -1
+	return nil
+}