Add unit tests for checker/scanner and validate input paths

- Add comprehensive unit tests for internal/checker (88.5% coverage)
  - Status string representations
  - NewChecker validation
  - Check operation (OK, missing, size/hash mismatch)
  - Progress reporting and context cancellation
  - FindExtraFiles functionality

- Add comprehensive unit tests for internal/scanner (80.1% coverage)
  - Constructors and options
  - File/path enumeration
  - Dotfile exclusion/inclusion
  - ToManifest with progress and cancellation
  - Non-blocking status channel sends

- Validate input paths before scanning in generate command
  - Fail fast with clear error if paths don't exist
  - Prevents confusing errors deep in enumeration

internal/checker/checker_test.go

@@ -0,0 +1,405 @@
+package checker
+
+import (
+	"bytes"
+	"context"
+	"testing"
+	"time"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/mfer/mfer"
+)
+
+func TestStatusString(t *testing.T) {
+	tests := []struct {
+		status   Status
+		expected string
+	}{
+		{StatusOK, "OK"},
+		{StatusMissing, "MISSING"},
+		{StatusSizeMismatch, "SIZE_MISMATCH"},
+		{StatusHashMismatch, "HASH_MISMATCH"},
+		{StatusExtra, "EXTRA"},
+		{StatusError, "ERROR"},
+		{Status(99), "UNKNOWN"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.expected, func(t *testing.T) {
+			assert.Equal(t, tt.expected, tt.status.String())
+		})
+	}
+}
+
+// createTestManifest creates a manifest file in the filesystem with the given files.
+func createTestManifest(t *testing.T, fs afero.Fs, manifestPath string, files map[string][]byte) {
+	t.Helper()
+
+	builder := mfer.NewBuilder()
+	for path, content := range files {
+		reader := bytes.NewReader(content)
+		_, err := builder.AddFile(path, int64(len(content)), time.Now(), reader, nil)
+		require.NoError(t, err)
+	}
+
+	var buf bytes.Buffer
+	require.NoError(t, builder.Build(&buf))
+	require.NoError(t, afero.WriteFile(fs, manifestPath, buf.Bytes(), 0644))
+}
+
+// createFilesOnDisk creates the given files on the filesystem.
+func createFilesOnDisk(t *testing.T, fs afero.Fs, basePath string, files map[string][]byte) {
+	t.Helper()
+
+	for path, content := range files {
+		fullPath := basePath + "/" + path
+		require.NoError(t, fs.MkdirAll(basePath, 0755))
+		require.NoError(t, afero.WriteFile(fs, fullPath, content, 0644))
+	}
+}
+
+func TestNewChecker(t *testing.T) {
+	t.Run("valid manifest", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		files := map[string][]byte{
+			"file1.txt": []byte("hello"),
+			"file2.txt": []byte("world"),
+		}
+		createTestManifest(t, fs, "/manifest.mf", files)
+
+		chk, err := NewChecker("/manifest.mf", "/", fs)
+		require.NoError(t, err)
+		assert.NotNil(t, chk)
+		assert.Equal(t, int64(2), chk.FileCount())
+	})
+
+	t.Run("missing manifest", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		_, err := NewChecker("/nonexistent.mf", "/", fs)
+		assert.Error(t, err)
+	})
+
+	t.Run("invalid manifest", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		require.NoError(t, afero.WriteFile(fs, "/bad.mf", []byte("not a manifest"), 0644))
+		_, err := NewChecker("/bad.mf", "/", fs)
+		assert.Error(t, err)
+	})
+}
+
+func TestCheckerFileCountAndTotalBytes(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"small.txt":  []byte("hi"),
+		"medium.txt": []byte("hello world"),
+		"large.txt":  bytes.Repeat([]byte("x"), 1000),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+
+	chk, err := NewChecker("/manifest.mf", "/", fs)
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(3), chk.FileCount())
+	assert.Equal(t, int64(2+11+1000), chk.TotalBytes())
+}
+
+func TestCheckAllFilesOK(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"file1.txt": []byte("content one"),
+		"file2.txt": []byte("content two"),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	var resultList []Result
+	for r := range results {
+		resultList = append(resultList, r)
+	}
+
+	assert.Len(t, resultList, 2)
+	for _, r := range resultList {
+		assert.Equal(t, StatusOK, r.Status, "file %s should be OK", r.Path)
+	}
+}
+
+func TestCheckMissingFile(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"exists.txt":  []byte("I exist"),
+		"missing.txt": []byte("I don't exist on disk"),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	// Only create one file
+	createFilesOnDisk(t, fs, "/data", map[string][]byte{
+		"exists.txt": []byte("I exist"),
+	})
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	var okCount, missingCount int
+	for r := range results {
+		switch r.Status {
+		case StatusOK:
+			okCount++
+		case StatusMissing:
+			missingCount++
+			assert.Equal(t, "missing.txt", r.Path)
+		}
+	}
+
+	assert.Equal(t, 1, okCount)
+	assert.Equal(t, 1, missingCount)
+}
+
+func TestCheckSizeMismatch(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"file.txt": []byte("original content"),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	// Create file with different size
+	createFilesOnDisk(t, fs, "/data", map[string][]byte{
+		"file.txt": []byte("short"),
+	})
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	r := <-results
+	assert.Equal(t, StatusSizeMismatch, r.Status)
+	assert.Equal(t, "file.txt", r.Path)
+}
+
+func TestCheckHashMismatch(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	originalContent := []byte("original content")
+	files := map[string][]byte{
+		"file.txt": originalContent,
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	// Create file with same size but different content
+	differentContent := []byte("different contnt") // same length (16 bytes) but different
+	require.Equal(t, len(originalContent), len(differentContent), "test requires same length")
+	createFilesOnDisk(t, fs, "/data", map[string][]byte{
+		"file.txt": differentContent,
+	})
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	r := <-results
+	assert.Equal(t, StatusHashMismatch, r.Status)
+	assert.Equal(t, "file.txt", r.Path)
+}
+
+func TestCheckWithProgress(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"file1.txt": bytes.Repeat([]byte("a"), 100),
+		"file2.txt": bytes.Repeat([]byte("b"), 200),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	progress := make(chan CheckStatus, 10)
+
+	err = chk.Check(context.Background(), results, progress)
+	require.NoError(t, err)
+
+	// Drain results
+	for range results {
+	}
+
+	// Check progress was sent
+	var progressUpdates []CheckStatus
+	for p := range progress {
+		progressUpdates = append(progressUpdates, p)
+	}
+
+	assert.NotEmpty(t, progressUpdates)
+	// Final progress should show all files checked
+	final := progressUpdates[len(progressUpdates)-1]
+	assert.Equal(t, int64(2), final.TotalFiles)
+	assert.Equal(t, int64(2), final.CheckedFiles)
+	assert.Equal(t, int64(300), final.TotalBytes)
+	assert.Equal(t, int64(300), final.CheckedBytes)
+	assert.Equal(t, int64(0), final.Failures)
+}
+
+func TestCheckContextCancellation(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	// Create many files to ensure we have time to cancel
+	files := make(map[string][]byte)
+	for i := 0; i < 100; i++ {
+		files[string(rune('a'+i%26))+".txt"] = bytes.Repeat([]byte("x"), 1000)
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // Cancel immediately
+
+	results := make(chan Result, 200)
+	err = chk.Check(ctx, results, nil)
+	assert.ErrorIs(t, err, context.Canceled)
+}
+
+func TestFindExtraFiles(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	// Manifest only contains file1
+	manifestFiles := map[string][]byte{
+		"file1.txt": []byte("in manifest"),
+	}
+	createTestManifest(t, fs, "/manifest.mf", manifestFiles)
+
+	// Disk has file1 and file2
+	createFilesOnDisk(t, fs, "/data", map[string][]byte{
+		"file1.txt": []byte("in manifest"),
+		"file2.txt": []byte("extra file"),
+	})
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.FindExtraFiles(context.Background(), results)
+	require.NoError(t, err)
+
+	var extras []Result
+	for r := range results {
+		extras = append(extras, r)
+	}
+
+	assert.Len(t, extras, 1)
+	assert.Equal(t, "file2.txt", extras[0].Path)
+	assert.Equal(t, StatusExtra, extras[0].Status)
+	assert.Equal(t, "not in manifest", extras[0].Message)
+}
+
+func TestFindExtraFilesContextCancellation(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{"file.txt": []byte("data")}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // Cancel immediately
+
+	results := make(chan Result, 10)
+	err = chk.FindExtraFiles(ctx, results)
+	assert.ErrorIs(t, err, context.Canceled)
+}
+
+func TestCheckNilChannels(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{"file.txt": []byte("data")}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	// Should not panic with nil channels
+	err = chk.Check(context.Background(), nil, nil)
+	assert.NoError(t, err)
+}
+
+func TestFindExtraFilesNilChannel(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{"file.txt": []byte("data")}
+	createTestManifest(t, fs, "/manifest.mf", files)
+	createFilesOnDisk(t, fs, "/data", files)
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	// Should not panic with nil channel
+	err = chk.FindExtraFiles(context.Background(), nil)
+	assert.NoError(t, err)
+}
+
+func TestCheckSubdirectories(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	files := map[string][]byte{
+		"dir1/file1.txt":          []byte("content1"),
+		"dir1/dir2/file2.txt":     []byte("content2"),
+		"dir1/dir2/dir3/deep.txt": []byte("deep content"),
+	}
+	createTestManifest(t, fs, "/manifest.mf", files)
+
+	// Create files with full directory structure
+	for path, content := range files {
+		fullPath := "/data/" + path
+		require.NoError(t, fs.MkdirAll("/data/dir1/dir2/dir3", 0755))
+		require.NoError(t, afero.WriteFile(fs, fullPath, content, 0644))
+	}
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	var okCount int
+	for r := range results {
+		assert.Equal(t, StatusOK, r.Status, "file %s should be OK", r.Path)
+		okCount++
+	}
+	assert.Equal(t, 3, okCount)
+}
+
+func TestCheckEmptyManifest(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	// Create manifest with no files
+	createTestManifest(t, fs, "/manifest.mf", map[string][]byte{})
+
+	chk, err := NewChecker("/manifest.mf", "/data", fs)
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(0), chk.FileCount())
+	assert.Equal(t, int64(0), chk.TotalBytes())
+
+	results := make(chan Result, 10)
+	err = chk.Check(context.Background(), results, nil)
+	require.NoError(t, err)
+
+	var count int
+	for range results {
+		count++
+	}
+	assert.Equal(t, 0, count)
+}

internal/cli/entry_test.go

@@ -485,6 +485,42 @@ func TestGenerateAtomicWriteCleansUpOnError(t *testing.T) {
 	assert.False(t, tmpExists, "temp file should be cleaned up after failed generation")
 }
 
+func TestGenerateValidatesInputPaths(t *testing.T) {
+	fs := afero.NewMemMapFs()
+
+	// Create one valid directory
+	require.NoError(t, fs.MkdirAll("/validdir", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/validdir/file.txt", []byte("content"), 0644))
+
+	t.Run("nonexistent path fails fast", func(t *testing.T) {
+		opts := testOpts([]string{"mfer", "generate", "-q", "-o", "/output.mf", "/nonexistent"}, fs)
+		exitCode := RunWithOptions(opts)
+		assert.Equal(t, 1, exitCode)
+		stderr := opts.Stderr.(*bytes.Buffer).String()
+		assert.Contains(t, stderr, "path does not exist")
+		assert.Contains(t, stderr, "/nonexistent")
+	})
+
+	t.Run("mix of valid and invalid paths fails fast", func(t *testing.T) {
+		opts := testOpts([]string{"mfer", "generate", "-q", "-o", "/output.mf", "/validdir", "/alsononexistent"}, fs)
+		exitCode := RunWithOptions(opts)
+		assert.Equal(t, 1, exitCode)
+		stderr := opts.Stderr.(*bytes.Buffer).String()
+		assert.Contains(t, stderr, "path does not exist")
+		assert.Contains(t, stderr, "/alsononexistent")
+
+		// Output file should not have been created
+		exists, _ := afero.Exists(fs, "/output.mf")
+		assert.False(t, exists, "output file should not exist when path validation fails")
+	})
+
+	t.Run("valid paths succeed", func(t *testing.T) {
+		opts := testOpts([]string{"mfer", "generate", "-q", "-o", "/output.mf", "/validdir"}, fs)
+		exitCode := RunWithOptions(opts)
+		assert.Equal(t, 0, exitCode)
+	})
+}
+
 func TestCheckDetectsManifestCorruption(t *testing.T) {
 	fs := afero.NewMemMapFs()
 	rng := rand.New(rand.NewSource(42))

internal/cli/gen.go

@@ -54,13 +54,18 @@ func (mfa *CLIApp) generateManifestOperation(ctx *cli.Context) error {
 			return err
 		}
 	} else {
-		// Collect all paths first
+		// Collect and validate all paths first
 		paths := make([]string, 0, args.Len())
 		for i := 0; i < args.Len(); i++ {
-			ap, err := filepath.Abs(args.Get(i))
+			inputPath := args.Get(i)
+			ap, err := filepath.Abs(inputPath)
 			if err != nil {
 				return err
 			}
+			// Validate path exists before adding to list
+			if exists, _ := afero.Exists(mfa.Fs, ap); !exists {
+				return fmt.Errorf("path does not exist: %s", inputPath)
+			}
 			log.Debugf("enumerating path: %s", ap)
 			paths = append(paths, ap)
 		}

internal/scanner/scanner_test.go

@@ -0,0 +1,362 @@
+package scanner
+
+import (
+	"bytes"
+	"context"
+	"testing"
+	"time"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNew(t *testing.T) {
+	s := New()
+	assert.NotNil(t, s)
+	assert.Equal(t, int64(0), s.FileCount())
+	assert.Equal(t, int64(0), s.TotalBytes())
+}
+
+func TestNewWithOptions(t *testing.T) {
+	t.Run("nil options", func(t *testing.T) {
+		s := NewWithOptions(nil)
+		assert.NotNil(t, s)
+	})
+
+	t.Run("with options", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		opts := &Options{
+			IncludeDotfiles: true,
+			FollowSymLinks:  true,
+			Fs:              fs,
+		}
+		s := NewWithOptions(opts)
+		assert.NotNil(t, s)
+	})
+}
+
+func TestEnumerateFile(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, afero.WriteFile(fs, "/test.txt", []byte("hello world"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumerateFile("/test.txt")
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(1), s.FileCount())
+	assert.Equal(t, int64(11), s.TotalBytes())
+
+	files := s.Files()
+	require.Len(t, files, 1)
+	assert.Equal(t, "test.txt", files[0].Path)
+	assert.Equal(t, int64(11), files[0].Size)
+}
+
+func TestEnumerateFileMissing(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumerateFile("/nonexistent.txt")
+	assert.Error(t, err)
+}
+
+func TestEnumeratePath(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir/subdir", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file1.txt", []byte("one"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file2.txt", []byte("two"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/subdir/file3.txt", []byte("three"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumeratePath("/testdir", nil)
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(3), s.FileCount())
+	assert.Equal(t, int64(3+3+5), s.TotalBytes())
+}
+
+func TestEnumeratePathWithProgress(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file1.txt", []byte("one"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file2.txt", []byte("two"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	progress := make(chan EnumerateStatus, 10)
+
+	err := s.EnumeratePath("/testdir", progress)
+	require.NoError(t, err)
+
+	var updates []EnumerateStatus
+	for p := range progress {
+		updates = append(updates, p)
+	}
+
+	assert.NotEmpty(t, updates)
+	// Final update should show all files
+	final := updates[len(updates)-1]
+	assert.Equal(t, int64(2), final.FilesFound)
+	assert.Equal(t, int64(6), final.BytesFound)
+}
+
+func TestEnumeratePaths(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/dir1", 0755))
+	require.NoError(t, fs.MkdirAll("/dir2", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/dir1/a.txt", []byte("aaa"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/dir2/b.txt", []byte("bbb"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumeratePaths(nil, "/dir1", "/dir2")
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(2), s.FileCount())
+}
+
+func TestExcludeDotfiles(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir/.hidden", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/visible.txt", []byte("visible"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/.hidden.txt", []byte("hidden"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/.hidden/inside.txt", []byte("inside"), 0644))
+
+	t.Run("exclude by default", func(t *testing.T) {
+		s := NewWithOptions(&Options{Fs: fs, IncludeDotfiles: false})
+		err := s.EnumeratePath("/testdir", nil)
+		require.NoError(t, err)
+
+		assert.Equal(t, int64(1), s.FileCount())
+		files := s.Files()
+		assert.Equal(t, "visible.txt", files[0].Path)
+	})
+
+	t.Run("include when enabled", func(t *testing.T) {
+		s := NewWithOptions(&Options{Fs: fs, IncludeDotfiles: true})
+		err := s.EnumeratePath("/testdir", nil)
+		require.NoError(t, err)
+
+		assert.Equal(t, int64(3), s.FileCount())
+	})
+}
+
+func TestPathIsHidden(t *testing.T) {
+	tests := []struct {
+		path   string
+		hidden bool
+	}{
+		{"file.txt", false},
+		{".hidden", true},
+		{"dir/file.txt", false},
+		{"dir/.hidden", true},
+		{".dir/file.txt", true},
+		{"/absolute/path", false},
+		{"/absolute/.hidden", true},
+		{"./relative", false}, // path.Clean removes leading ./
+		{"a/b/c/.d/e", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			assert.Equal(t, tt.hidden, pathIsHidden(tt.path), "pathIsHidden(%q)", tt.path)
+		})
+	}
+}
+
+func TestToManifest(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file1.txt", []byte("content one"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file2.txt", []byte("content two"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumeratePath("/testdir", nil)
+	require.NoError(t, err)
+
+	var buf bytes.Buffer
+	err = s.ToManifest(context.Background(), &buf, nil)
+	require.NoError(t, err)
+
+	// Manifest should have magic bytes
+	assert.True(t, buf.Len() > 0)
+	assert.Equal(t, "ZNAVSRFG", string(buf.Bytes()[:8]))
+}
+
+func TestToManifestWithProgress(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file.txt", bytes.Repeat([]byte("x"), 1000), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumeratePath("/testdir", nil)
+	require.NoError(t, err)
+
+	var buf bytes.Buffer
+	progress := make(chan ScanStatus, 10)
+
+	err = s.ToManifest(context.Background(), &buf, progress)
+	require.NoError(t, err)
+
+	var updates []ScanStatus
+	for p := range progress {
+		updates = append(updates, p)
+	}
+
+	assert.NotEmpty(t, updates)
+	// Final update should show completion
+	final := updates[len(updates)-1]
+	assert.Equal(t, int64(1), final.TotalFiles)
+	assert.Equal(t, int64(1), final.ScannedFiles)
+	assert.Equal(t, int64(1000), final.TotalBytes)
+	assert.Equal(t, int64(1000), final.ScannedBytes)
+}
+
+func TestToManifestContextCancellation(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir", 0755))
+	// Create many files to ensure we have time to cancel
+	for i := 0; i < 100; i++ {
+		name := string(rune('a'+i%26)) + string(rune('0'+i/26)) + ".txt"
+		require.NoError(t, afero.WriteFile(fs, "/testdir/"+name, bytes.Repeat([]byte("x"), 100), 0644))
+	}
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumeratePath("/testdir", nil)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // Cancel immediately
+
+	var buf bytes.Buffer
+	err = s.ToManifest(ctx, &buf, nil)
+	assert.ErrorIs(t, err, context.Canceled)
+}
+
+func TestToManifestEmptyScanner(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	s := NewWithOptions(&Options{Fs: fs})
+
+	var buf bytes.Buffer
+	err := s.ToManifest(context.Background(), &buf, nil)
+	require.NoError(t, err)
+
+	// Should still produce a valid manifest
+	assert.True(t, buf.Len() > 0)
+	assert.Equal(t, "ZNAVSRFG", string(buf.Bytes()[:8]))
+}
+
+func TestFilesCopiesSlice(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, afero.WriteFile(fs, "/test.txt", []byte("hello"), 0644))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	require.NoError(t, s.EnumerateFile("/test.txt"))
+
+	files1 := s.Files()
+	files2 := s.Files()
+
+	// Should be different slices
+	assert.NotSame(t, &files1[0], &files2[0])
+}
+
+func TestEnumerateFS(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir/sub", 0755))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/file.txt", []byte("hello"), 0644))
+	require.NoError(t, afero.WriteFile(fs, "/testdir/sub/nested.txt", []byte("world"), 0644))
+
+	// Create a basepath filesystem
+	baseFs := afero.NewBasePathFs(fs, "/testdir")
+
+	s := NewWithOptions(&Options{Fs: fs})
+	err := s.EnumerateFS(baseFs, "/testdir", nil)
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(2), s.FileCount())
+}
+
+func TestSendEnumerateStatusNonBlocking(t *testing.T) {
+	// Channel with no buffer - send should not block
+	ch := make(chan EnumerateStatus)
+
+	// This should not block
+	done := make(chan bool)
+	go func() {
+		sendEnumerateStatus(ch, EnumerateStatus{FilesFound: 1})
+		done <- true
+	}()
+
+	select {
+	case <-done:
+		// Success - did not block
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("sendEnumerateStatus blocked on full channel")
+	}
+}
+
+func TestSendScanStatusNonBlocking(t *testing.T) {
+	// Channel with no buffer - send should not block
+	ch := make(chan ScanStatus)
+
+	done := make(chan bool)
+	go func() {
+		sendScanStatus(ch, ScanStatus{ScannedFiles: 1})
+		done <- true
+	}()
+
+	select {
+	case <-done:
+		// Success - did not block
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("sendScanStatus blocked on full channel")
+	}
+}
+
+func TestSendStatusNilChannel(t *testing.T) {
+	// Should not panic with nil channel
+	sendEnumerateStatus(nil, EnumerateStatus{})
+	sendScanStatus(nil, ScanStatus{})
+}
+
+func TestFileEntryFields(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	now := time.Now().Truncate(time.Second)
+	require.NoError(t, afero.WriteFile(fs, "/test.txt", []byte("content"), 0644))
+	require.NoError(t, fs.Chtimes("/test.txt", now, now))
+
+	s := NewWithOptions(&Options{Fs: fs})
+	require.NoError(t, s.EnumerateFile("/test.txt"))
+
+	files := s.Files()
+	require.Len(t, files, 1)
+
+	entry := files[0]
+	assert.Equal(t, "test.txt", entry.Path)
+	assert.Contains(t, entry.AbsPath, "test.txt")
+	assert.Equal(t, int64(7), entry.Size)
+	// Mtime should be set (within a second of now)
+	assert.WithinDuration(t, now, entry.Mtime, 2*time.Second)
+}
+
+func TestLargeFileEnumeration(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/testdir", 0755))
+
+	// Create 100 files
+	for i := 0; i < 100; i++ {
+		name := "/testdir/" + string(rune('a'+i%26)) + string(rune('0'+i/26%10)) + ".txt"
+		require.NoError(t, afero.WriteFile(fs, name, []byte("data"), 0644))
+	}
+
+	s := NewWithOptions(&Options{Fs: fs})
+	progress := make(chan EnumerateStatus, 200)
+
+	err := s.EnumeratePath("/testdir", progress)
+	require.NoError(t, err)
+
+	// Drain channel
+	for range progress {
+	}
+
+	assert.Equal(t, int64(100), s.FileCount())
+	assert.Equal(t, int64(400), s.TotalBytes()) // 100 * 4 bytes
+}