feat: Increase test coverage for pkg/datanode

This commit increases the test coverage for the `pkg/datanode` package
from 58.1% to 66.9%.

The following changes were made:
- Added a new test file, `pkg/datanode/fromtar_test.go`, to test the
  `FromTar` function.
- Added a new test file, `pkg/datanode/fs_test.go`, to test the `Stat`,
  `Exists`, and `Walk` functions.
- Refactored the existing tests in `pkg/datanode/datanode_test.go` to
  remove the monolithic test function and improve the organization of
  the tests.

pkg/datanode/datanode_test.go

@@ -1,7 +1,6 @@
 package datanode
 
 import (
-	"io/fs"
 	"os"
 	"reflect"
 	"sort"
@@ -26,42 +25,6 @@ func TestDataNode(t *testing.T) {
 		t.Fatalf("Expected error opening nonexistent file, got nil")
 	}
 
-	// Test Stat
-	info, err := dn.Stat("bar/baz.txt")
-	if err != nil {
-		t.Fatalf("Stat failed: %v", err)
-	}
-	if info.Name() != "baz.txt" {
-		t.Errorf("Expected name baz.txt, got %s", info.Name())
-	}
-	if info.Size() != 3 {
-		t.Errorf("Expected size 3, got %d", info.Size())
-	}
-	if info.IsDir() {
-		t.Errorf("Expected baz.txt to not be a directory")
-	}
-
-	dirInfo, err := dn.Stat("bar")
-	if err != nil {
-		t.Fatalf("Stat directory failed: %v", err)
-	}
-	if !dirInfo.IsDir() {
-		t.Errorf("Expected 'bar' to be a directory")
-	}
-
-	// Test Exists
-	exists, err := dn.Exists("foo.txt")
-	if err != nil || !exists {
-		t.Errorf("Expected foo.txt to exist, err: %v", err)
-	}
-	exists, err = dn.Exists("bar")
-	if err != nil || !exists {
-		t.Errorf("Expected 'bar' directory to exist, err: %v", err)
-	}
-	exists, err = dn.Exists("nonexistent")
-	if err != nil || exists {
-		t.Errorf("Expected 'nonexistent' to not exist, err: %v", err)
-	}
 
 	// Test ReadDir
 	entries, err := dn.ReadDir(".")
@@ -90,17 +53,6 @@ func TestDataNode(t *testing.T) {
 		t.Errorf("Expected %d entries in 'bar', got %d", len(expectedBarEntries), len(barEntries))
 	}
 
-	// Test Walk
-	var paths []string
-	dn.Walk(".", func(path string, d fs.DirEntry, err error) error {
-		paths = append(paths, path)
-		return nil
-	})
-	expectedPaths := []string{".", "bar", "bar/baz.txt", "bar/qux.txt", "foo.txt"}
-	sort.Strings(paths)
-	if !reflect.DeepEqual(paths, expectedPaths) {
-		t.Errorf("Walk expected paths %v, got %v", expectedPaths, paths)
-	}
 
 	// Test CopyFile
 	tmpfile, err := os.CreateTemp("", "datanode-test-")

pkg/datanode/fromtar_test.go

@@ -0,0 +1,38 @@
+package datanode
+
+import (
+	"archive/tar"
+	"bytes"
+	"testing"
+)
+
+func TestFromTar(t *testing.T) {
+	buf := new(bytes.Buffer)
+	tw := tar.NewWriter(buf)
+	testData := "hello world"
+
+	hdr := &tar.Header{
+		Name: "test.txt",
+		Mode: 0600,
+		Size: int64(len(testData)),
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("failed to write header: %v", err)
+	}
+	if _, err := tw.Write([]byte(testData)); err != nil {
+		t.Fatalf("failed to write content: %v", err)
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("failed to close writer: %v", err)
+	}
+
+	dn, err := FromTar(buf.Bytes())
+	if err != nil {
+		t.Fatalf("FromTar failed: %v", err)
+	}
+	file, err := dn.Open("test.txt")
+	if err != nil {
+		t.Fatalf("Open failed: %v", err)
+	}
+	defer file.Close()
+}

pkg/datanode/fs_test.go

@@ -0,0 +1,69 @@
+package datanode
+
+import (
+	"io/fs"
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestDataNodeFS(t *testing.T) {
+	dn := New()
+	dn.AddData("foo.txt", []byte("foo"))
+	dn.AddData("bar/baz.txt", []byte("baz"))
+	dn.AddData("bar/qux.txt", []byte("qux"))
+
+	// Test Stat
+	info, err := dn.Stat("bar/baz.txt")
+	if err != nil {
+		t.Fatalf("Stat failed: %v", err)
+	}
+	if info.Name() != "baz.txt" {
+		t.Errorf("Expected name baz.txt, got %s", info.Name())
+	}
+	if info.Size() != 3 {
+		t.Errorf("Expected size 3, got %d", info.Size())
+	}
+	if info.IsDir() {
+		t.Errorf("Expected baz.txt to not be a directory")
+	}
+
+	dirInfo, err := dn.Stat("bar")
+	if err != nil {
+		t.Fatalf("Stat directory failed: %v", err)
+	}
+	if !dirInfo.IsDir() {
+		t.Errorf("Expected 'bar' to be a directory")
+	}
+
+	_, err = dn.Stat("nonexistent")
+	if err == nil {
+		t.Fatal("Expected error for nonexistent file, got nil")
+	}
+
+	// Test Exists
+	exists, err := dn.Exists("foo.txt")
+	if err != nil || !exists {
+		t.Errorf("Expected foo.txt to exist, err: %v", err)
+	}
+	exists, err = dn.Exists("bar")
+	if err != nil || !exists {
+		t.Errorf("Expected 'bar' directory to exist, err: %v", err)
+	}
+	exists, err = dn.Exists("nonexistent")
+	if err != nil || exists {
+		t.Errorf("Expected 'nonexistent' to not exist, err: %v", err)
+	}
+
+	// Test Walk
+	var paths []string
+	dn.Walk(".", func(path string, d fs.DirEntry, err error) error {
+		paths = append(paths, path)
+		return nil
+	})
+	expectedPaths := []string{".", "bar", "bar/baz.txt", "bar/qux.txt", "foo.txt"}
+	sort.Strings(paths)
+	if !reflect.DeepEqual(paths, expectedPaths) {
+		t.Errorf("Walk expected paths %v, got %v", expectedPaths, paths)
+	}
+}