diff --git a/pkg/oci-delta/datasource_test.go b/pkg/oci-delta/datasource_test.go
new file mode 100644
index 0000000..6afba0d
--- /dev/null
+++ b/pkg/oci-delta/datasource_test.go
@@ -0,0 +1,320 @@
+package ocidelta
+
+import (
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestNewFilesystemDataSource(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	ds := NewFilesystemDataSource(tmpDir)
+	if ds == nil {
+		t.Fatal("NewFilesystemDataSource returned nil")
+	}
+
+	if err := ds.Cleanup(); err != nil {
+		t.Errorf("Cleanup() failed: %v", err)
+	}
+
+	if err := ds.Close(); err != nil {
+		t.Errorf("Close() failed: %v", err)
+	}
+}
+
+func TestSimpleDataSourceCleanup(t *testing.T) {
+	tmpDir := t.TempDir()
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Close()
+
+	if err := ds.Cleanup(); err != nil {
+		t.Errorf("first Cleanup() = %v, want nil", err)
+	}
+
+	// Test idempotency - calling multiple times should be safe
+	if err := ds.Cleanup(); err != nil {
+		t.Errorf("second Cleanup() = %v, want nil", err)
+	}
+
+	if err := ds.Cleanup(); err != nil {
+		t.Errorf("third Cleanup() = %v, want nil", err)
+	}
+}
+
+func TestSimpleDataSourceWithValidDirectory(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create a test file in the directory
+	testFile := filepath.Join(tmpDir, "test.txt")
+	testContent := []byte("hello world")
+	if err := os.WriteFile(testFile, testContent, 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	// Set current file
+	if err := ds.SetCurrentFile("test.txt"); err != nil {
+		t.Fatalf("SetCurrentFile() failed: %v", err)
+	}
+
+	// Read the file content
+	buf := make([]byte, len(testContent))
+
+	n, err := ds.Read(buf)
+	if err != nil && !errors.Is(err, io.EOF) {
+		t.Fatalf("Read() failed: %v", err)
+	}
+
+	if n != len(testContent) {
+		t.Errorf("Read() returned %d bytes, want %d", n, len(testContent))
+	}
+
+	if string(buf) != string(testContent) {
+		t.Errorf("Read() content = %q, want %q", buf, testContent)
+	}
+}
+
+func TestSimpleDataSourceSeek(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create a test file
+	testFile := filepath.Join(tmpDir, "seektest.txt")
+	testContent := []byte("0123456789")
+	if err := os.WriteFile(testFile, testContent, 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	if err := ds.SetCurrentFile("seektest.txt"); err != nil {
+		t.Fatalf("SetCurrentFile() failed: %v", err)
+	}
+
+	// Seek to offset 5
+	pos, err := ds.Seek(5, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek() failed: %v", err)
+	}
+
+	if pos != 5 {
+		t.Errorf("Seek() position = %d, want 5", pos)
+	}
+
+	// Read from offset 5
+	buf := make([]byte, 5)
+
+	n, err := ds.Read(buf)
+	if err != nil && !errors.Is(err, io.EOF) {
+		t.Fatalf("Read() after Seek() failed: %v", err)
+	}
+
+	expected := "56789"
+	if string(buf[:n]) != expected {
+		t.Errorf("Read() after Seek() = %q, want %q", buf[:n], expected)
+	}
+
+	// Seek back to start
+	pos, err = ds.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek() to start failed: %v", err)
+	}
+
+	if pos != 0 {
+		t.Errorf("Seek() to start position = %d, want 0", pos)
+	}
+}
+
+func TestSimpleDataSourceClose(t *testing.T) {
+	tmpDir := t.TempDir()
+	ds := NewFilesystemDataSource(tmpDir)
+
+	if err := ds.Close(); err != nil {
+		t.Errorf("Close() = %v, want nil", err)
+	}
+
+	// Test idempotency - calling multiple times should be safe
+	if err := ds.Close(); err != nil {
+		t.Errorf("second Close() = %v, want nil", err)
+	}
+}
+
+func TestSimpleDataSourceReadAfterClose(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	testFile := filepath.Join(tmpDir, "test.txt")
+	if err := os.WriteFile(testFile, []byte("hello"), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+
+	if err := ds.SetCurrentFile("test.txt"); err != nil {
+		t.Fatalf("SetCurrentFile() failed: %v", err)
+	}
+
+	if err := ds.Close(); err != nil {
+		t.Fatalf("Close() failed: %v", err)
+	}
+
+	buf := make([]byte, 5)
+
+	_, err := ds.Read(buf)
+	if err == nil {
+		t.Error("Read() after Close() should return an error")
+	}
+}
+
+func TestSimpleDataSourceMultipleFiles(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create multiple test files
+	files := map[string]string{
+		"file1.txt": "content1",
+		"file2.txt": "content2",
+		"file3.txt": "content3",
+	}
+
+	for name, content := range files {
+		path := filepath.Join(tmpDir, name)
+		if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+			t.Fatalf("failed to write test file %q: %v", name, err)
+		}
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	// Test reading each file
+	for name, expectedContent := range files {
+		if err := ds.SetCurrentFile(name); err != nil {
+			t.Errorf("SetCurrentFile(%q) = %v, want nil", name, err)
+			continue
+		}
+
+		buf := make([]byte, len(expectedContent))
+
+		n, err := ds.Read(buf)
+		if err != nil && !errors.Is(err, io.EOF) {
+			t.Errorf("Read() for %q failed: %v", name, err)
+			continue
+		}
+
+		if string(buf[:n]) != expectedContent {
+			t.Errorf("Read() for %q = %q, want %q", name, buf[:n], expectedContent)
+		}
+	}
+}
+
+func TestSimpleDataSourceReadWithoutSetCurrentFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	buf := make([]byte, 10)
+
+	_, err := ds.Read(buf)
+	if err == nil {
+		t.Error("Read() without SetCurrentFile() should return an error")
+	}
+}
+
+func TestSimpleDataSourceSeekWithoutSetCurrentFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	_, err := ds.Seek(0, io.SeekStart)
+	if err == nil {
+		t.Error("Seek() without SetCurrentFile() should return an error")
+	}
+}
+
+func TestSimpleDataSourceNonexistentFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	// Try to set a nonexistent file
+	err := ds.SetCurrentFile("does-not-exist.txt")
+	if err == nil {
+		t.Error("SetCurrentFile() for nonexistent file should fail")
+	}
+}
+
+func TestSimpleDataSourceSubdirectory(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create subdirectory with file
+	subDir := filepath.Join(tmpDir, "subdir")
+	if err := os.Mkdir(subDir, 0755); err != nil {
+		t.Fatalf("failed to create subdirectory: %v", err)
+	}
+
+	testFile := filepath.Join(subDir, "nested.txt")
+	testContent := []byte("nested content")
+	if err := os.WriteFile(testFile, testContent, 0644); err != nil {
+		t.Fatalf("failed to write nested test file: %v", err)
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	// Access file in subdirectory
+	if err := ds.SetCurrentFile("subdir/nested.txt"); err != nil {
+		t.Fatalf("SetCurrentFile() for nested file failed: %v", err)
+	}
+
+	buf := make([]byte, len(testContent))
+
+	n, err := ds.Read(buf)
+	if err != nil && !errors.Is(err, io.EOF) {
+		t.Fatalf("Read() for nested file failed: %v", err)
+	}
+
+	if string(buf[:n]) != string(testContent) {
+		t.Errorf("Read() for nested file = %q, want %q", buf[:n], testContent)
+	}
+}
+
+func TestSimpleDataSourceEmptyFile(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create an empty file
+	emptyFile := filepath.Join(tmpDir, "empty.txt")
+	if err := os.WriteFile(emptyFile, []byte{}, 0644); err != nil {
+		t.Fatalf("failed to write empty test file: %v", err)
+	}
+
+	ds := NewFilesystemDataSource(tmpDir)
+	defer ds.Cleanup()
+	defer ds.Close()
+
+	if err := ds.SetCurrentFile("empty.txt"); err != nil {
+		t.Fatalf("SetCurrentFile() for empty file failed: %v", err)
+	}
+
+	buf := make([]byte, 10)
+
+	n, err := ds.Read(buf)
+	if !errors.Is(err, io.EOF) {
+		t.Errorf("Read() for empty file error = %v, want io.EOF", err)
+	}
+
+	if n != 0 {
+		t.Errorf("Read() for empty file returned %d bytes, want 0", n)
+	}
+}