Finish writing tests

a/a-test.txt

@@ -0,0 +1 @@
+Nothing

a/example.md

@@ -0,0 +1 @@
+# This is an example

a/hello.txt

@@ -1 +1 @@
-Empty
+Empty

a/just-a.txt

@@ -1 +1 @@
-A
+A

b/hello.txt

@@ -1 +1 @@
-Hello World!
+Hello World!

b/just-b.txt

@@ -1 +1 @@
-B
+B

overlapfs.go

@@ -2,15 +2,16 @@ package overlapfs
 
 import (
 	"errors"
-	"fmt"
 	"io/fs"
+	"slices"
+	"strings"
 )
 
 // OverlapFS layers B on top of A
 //
-// Open and Stat reimplemented to show B unless ErrNotExist is returned then show A.
+// Open and Stat reimplemented to show B unless ErrNotExist is returned then show A
 //
-// Glob and ReadDir are reimplemented to uniquely merge the returned lists.
+// Glob and ReadDir are reimplemented to uniquely merge and sort the returned slices
 //
 // For ReadFile and Sub use the standard fs.ReadFile and fs.Sub implementations
 type OverlapFS struct {
@@ -24,8 +25,9 @@ var _ interface {
 	fs.ReadDirFS
 } = &OverlapFS{}
 
+// Open implements fs.FS, the file named will be read from B if the file exists,
+// otherwise the file named will be read from A
 func (o OverlapFS) Open(name string) (fs.File, error) {
-	fmt.Println("Open", name)
 	open, err := o.B.Open(name)
 	switch {
 	case err == nil:
@@ -36,6 +38,8 @@ func (o OverlapFS) Open(name string) (fs.File, error) {
 	return nil, err
 }
 
+// Stat implements fs.StatFS, the file named will have stats read from B if the
+// file exists, otherwise the file named will have stats read from A
 func (o OverlapFS) Stat(name string) (fs.FileInfo, error) {
 	stat, err := fs.Stat(o.B, name)
 	switch {
@@ -47,36 +51,39 @@ func (o OverlapFS) Stat(name string) (fs.FileInfo, error) {
 	return nil, err
 }
 
+// Glob implements fs.GlobFS, the pattern will be globed in B and A and the
+// result uniquely merged and sorted
 func (o OverlapFS) Glob(pattern string) ([]string, error) {
-	aSlice, err := fs.Glob(o.B, pattern)
+	bSlice, err := fs.Glob(o.B, pattern)
 	if err != nil {
 		return nil, err
 	}
-	bSlice, err := fs.Glob(o.A, pattern)
+	aSlice, err := fs.Glob(o.A, pattern)
 	if err != nil {
 		return nil, err
 	}
 
-	mergeUnique(aSlice, bSlice, func(s string) string { return s })
-	return aSlice, nil
+	return mergeUnique(aSlice, bSlice, func(s string) string { return s }), nil
 }
 
+// ReadDir implements fs.ReadDirFS, the directory named will be read in B and A
+// and the result uniquely merged and sorted
 func (o OverlapFS) ReadDir(name string) ([]fs.DirEntry, error) {
-	aSlice, err := fs.ReadDir(o.B, name)
+	bSlice, err := fs.ReadDir(o.B, name)
 	if err != nil {
 		return nil, err
 	}
-	bSlice, err := fs.ReadDir(o.A, name)
+	aSlice, err := fs.ReadDir(o.A, name)
 	if err != nil {
 		return nil, err
 	}
 
-	mergeUnique(aSlice, bSlice, func(entry fs.DirEntry) string { return entry.Name() })
-	return aSlice, nil
+	return mergeUnique(aSlice, bSlice, func(entry fs.DirEntry) string { return entry.Name() }), nil
 }
 
-// mergeUnique puts unique values from b into a
-func mergeUnique[T any](a, b []T, key func(T) string) {
+// mergeUnique puts unique values from b into a and sorts the resulting merged
+// slice
+func mergeUnique[T any](a, b []T, key func(T) string) []T {
 	m := make(map[string]struct{})
 	for _, i := range a {
 		m[key(i)] = struct{}{}
@@ -86,4 +93,8 @@ func mergeUnique[T any](a, b []T, key func(T) string) {
 			a = append(a, i)
 		}
 	}
+	slices.SortFunc(a, func(a, b T) int {
+		return strings.Compare(key(a), key(b))
+	})
+	return a
 }

overlapfs_test.go

@@ -16,16 +16,32 @@ func TestOverlapFS_Open(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "hello.txt", stat.Name())
 	bAll, err := io.ReadAll(open)
-	assert.Equal(t, "Hello World!", string(bAll))
+	assert.Equal(t, "Hello World!\n", string(bAll))
 }
 
 func TestOverlapFS_Stat(t *testing.T) {
 	o := OverlapFS{A: a.Embed, B: b.Embed}
-	open, err := o.Stat("hello.txt")
-	assert.NoError(t, err)
-	stat, err := open.Stat()
+	stat, err := o.Stat("hello.txt")
 	assert.NoError(t, err)
 	assert.Equal(t, "hello.txt", stat.Name())
-	bAll, err := io.ReadAll(open)
-	assert.Equal(t, "Hello World!", string(bAll))
+	assert.Equal(t, int64(13), stat.Size())
+	assert.False(t, stat.IsDir())
+}
+
+func TestOverlapFS_Glob(t *testing.T) {
+	o := OverlapFS{A: a.Embed, B: b.Embed}
+	glob, err := o.Glob("*.txt")
+	assert.NoError(t, err)
+	assert.Equal(t, []string{"a-test.txt", "hello.txt", "just-a.txt", "just-b.txt"}, glob)
+}
+
+func TestOverlapFS_ReadDir(t *testing.T) {
+	o := OverlapFS{A: a.Embed, B: b.Embed}
+	dir, err := o.ReadDir(".")
+	assert.NoError(t, err)
+	z := make([]string, 0, len(dir))
+	for _, i := range dir {
+		z = append(z, i.Name())
+	}
+	assert.Equal(t, []string{"a-test.txt", "a.go", "b.go", "example.md", "hello.txt", "just-a.txt", "just-b.txt"}, z)
 }