diff --git a/app/fs_test.go b/app/fs_test.go
new file mode 100644
index 0000000..c8f9ea0
--- /dev/null
+++ b/app/fs_test.go
@@ -0,0 +1,233 @@
+package app
+
+import (
+	"context"
+	"testing"
+	"os"
+	"path/filepath"
+	"time"
+	"strconv"
+)
+
+func TestDirResolveUser(t *testing.T) {
+	configTmp := createTestConfig("/tmp")
+
+	ctx := context.Background()
+	admin := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "admin", Authenticated: true})
+	user1 := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "user1", Authenticated: true})
+	anon := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "user1", Authenticated: false})
+
+	tests := []struct {
+		name string
+		ctx  context.Context
+		want string
+	}{
+		{"", admin, "admin"},
+		{"", user1, "user1"},
+		{"", anon, ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d := Dir{
+				Config: configTmp,
+			}
+			if got := d.resolveUser(tt.ctx); got != tt.want {
+				t.Errorf("Dir.resolveUser() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestDirResolve(t *testing.T) {
+	configTmp := createTestConfig("/tmp")
+	configRoot := createTestConfig("/")
+	configCurrentDir := createTestConfig(".")
+	configEmpty := createTestConfig("")
+
+	ctx := context.Background()
+	admin := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "admin", Authenticated: true})
+	user1 := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "user1", Authenticated: true})
+	user2 := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "user2", Authenticated: true})
+
+	tests := []struct {
+		cfg  *Config
+		name string
+		ctx  context.Context
+		want string
+	}{
+		{configTmp, "", admin, "/tmp"},
+		{configTmp, ".", admin, "/tmp"},
+		{configTmp, "/", admin, "/tmp"},
+		{configTmp, "./a", admin, "/tmp/a"},
+		{configTmp, "..", admin, "/tmp"},
+		{configTmp, "../", admin, "/tmp"},
+		{configTmp, "../.", admin, "/tmp"},
+		{configTmp, "../a", admin, "/tmp/a"},
+		{configTmp, "../..", admin, "/tmp"},
+		{configTmp, "../bar/a", admin, "/tmp/bar/a"},
+		{configTmp, "../baz/a", admin, "/tmp/baz/a"},
+		{configTmp, "...", admin, "/tmp/..."},
+		{configTmp, ".../a", admin, "/tmp/.../a"},
+		{configTmp, ".../..", admin, "/tmp"},
+		{configTmp, "a", admin, "/tmp/a"},
+		{configTmp, "a/./b", admin, "/tmp/a/b"},
+		{configTmp, "a/../../b", admin, "/tmp/b"},
+		{configTmp, "a/../b", admin, "/tmp/b"},
+		{configTmp, "a/b", admin, "/tmp/a/b"},
+		{configTmp, "a/b/c/../../d", admin, "/tmp/a/d"},
+		{configTmp, "a/b/c/../../../d", admin, "/tmp/d"},
+		{configTmp, "a/b/c/../../../../d", admin, "/tmp/d"},
+		{configTmp, "a/b/c/d", admin, "/tmp/a/b/c/d"},
+		{configTmp, "/a/b/c/d", admin, "/tmp/a/b/c/d"},
+
+		{configTmp, "ab/c\x00d/ef", admin, ""},
+
+		{configRoot, "", admin, "/"},
+		{configRoot, ".", admin, "/"},
+		{configRoot, "/", admin, "/"},
+		{configRoot, "./a", admin, "/a"},
+		{configRoot, "..", admin, "/"},
+		{configRoot, "../", admin, "/"},
+		{configRoot, "../.", admin, "/"},
+		{configRoot, "../a", admin, "/a"},
+		{configRoot, "../..", admin, "/"},
+		{configRoot, "../bar/a", admin, "/bar/a"},
+		{configRoot, "../baz/a", admin, "/baz/a"},
+		{configRoot, "...", admin, "/..."},
+		{configRoot, ".../a", admin, "/.../a"},
+		{configRoot, ".../..", admin, "/"},
+		{configRoot, "a", admin, "/a"},
+		{configRoot, "a/./b", admin, "/a/b"},
+		{configRoot, "a/../../b", admin, "/b"},
+		{configRoot, "a/../b", admin, "/b"},
+		{configRoot, "a/b", admin, "/a/b"},
+		{configRoot, "a/b/c/../../d", admin, "/a/d"},
+		{configRoot, "a/b/c/../../../d", admin, "/d"},
+		{configRoot, "a/b/c/../../../../d", admin, "/d"},
+		{configRoot, "a/b/c/d", admin, "/a/b/c/d"},
+		{configRoot, "/a/b/c/d", admin, "/a/b/c/d"},
+
+		{configCurrentDir, "", admin, "."},
+		{configCurrentDir, ".", admin, "."},
+		{configCurrentDir, "/", admin, "."},
+		{configCurrentDir, "./a", admin, "a"},
+		{configCurrentDir, "..", admin, "."},
+		{configCurrentDir, "../", admin, "."},
+		{configCurrentDir, "../.", admin, "."},
+		{configCurrentDir, "../a", admin, "a"},
+		{configCurrentDir, "../..", admin, "."},
+		{configCurrentDir, "../bar/a", admin, "bar/a"},
+		{configCurrentDir, "../baz/a", admin, "baz/a"},
+		{configCurrentDir, "...", admin, "..."},
+		{configCurrentDir, ".../a", admin, ".../a"},
+		{configCurrentDir, ".../..", admin, "."},
+		{configCurrentDir, "a", admin, "a"},
+		{configCurrentDir, "a/./b", admin, "a/b"},
+		{configCurrentDir, "a/../../b", admin, "b"},
+		{configCurrentDir, "a/../b", admin, "b"},
+		{configCurrentDir, "a/b", admin, "a/b"},
+		{configCurrentDir, "a/b/c/../../d", admin, "a/d"},
+		{configCurrentDir, "a/b/c/../../../d", admin, "d"},
+		{configCurrentDir, "a/b/c/../../../../d", admin, "d"},
+		{configCurrentDir, "a/b/c/d", admin, "a/b/c/d"},
+		{configCurrentDir, "/a/b/c/d", admin, "a/b/c/d"},
+
+		{configEmpty, "", admin, "."},
+
+		{configTmp, "", user1, "/tmp/subdir1"},
+		{configTmp, ".", user1, "/tmp/subdir1"},
+		{configTmp, "/", user1, "/tmp/subdir1"},
+		{configTmp, "./a", user1, "/tmp/subdir1/a"},
+		{configTmp, "..", user1, "/tmp/subdir1"},
+		{configTmp, "../", user1, "/tmp/subdir1"},
+		{configTmp, "../.", user1, "/tmp/subdir1"},
+		{configTmp, "../a", user1, "/tmp/subdir1/a"},
+		{configTmp, "../..", user1, "/tmp/subdir1"},
+		{configTmp, "../bar/a", user1, "/tmp/subdir1/bar/a"},
+		{configTmp, "../baz/a", user1, "/tmp/subdir1/baz/a"},
+		{configTmp, "...", user1, "/tmp/subdir1/..."},
+		{configTmp, ".../a", user1, "/tmp/subdir1/.../a"},
+		{configTmp, ".../..", user1, "/tmp/subdir1"},
+		{configTmp, "a", user1, "/tmp/subdir1/a"},
+		{configTmp, "a/./b", user1, "/tmp/subdir1/a/b"},
+		{configTmp, "a/../../b", user1, "/tmp/subdir1/b"},
+		{configTmp, "a/../b", user1, "/tmp/subdir1/b"},
+		{configTmp, "a/b", user1, "/tmp/subdir1/a/b"},
+		{configTmp, "a/b/c/../../d", user1, "/tmp/subdir1/a/d"},
+		{configTmp, "a/b/c/../../../d", user1, "/tmp/subdir1/d"},
+		{configTmp, "a/b/c/../../../../d", user1, "/tmp/subdir1/d"},
+		{configTmp, "a/b/c/d", user1, "/tmp/subdir1/a/b/c/d"},
+		{configTmp, "/a/b/c/d", user1, "/tmp/subdir1/a/b/c/d"},
+		{configTmp, "", user2, "/tmp/subdir2"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d := Dir{
+				Config: tt.cfg,
+			}
+			if got := d.resolve(tt.ctx, tt.name); got != tt.want {
+				t.Errorf("Dir.resolve() = %v, want %v. Base dir is %v", got, tt.want, tt.cfg.Dir)
+			}
+		})
+	}
+}
+
+func TestDirMkdir(t *testing.T) {
+	tmpDir := filepath.Join(os.TempDir(), "dave__"+strconv.FormatInt(time.Now().Unix(), 10))
+	os.Mkdir(tmpDir, 0700)
+	defer os.RemoveAll(tmpDir)
+
+	t.Logf("using test dir: %s", tmpDir)
+	configTmp := createTestConfig(tmpDir)
+
+	ctx := context.Background()
+	admin := context.WithValue(ctx, authInfoKey, &AuthInfo{Username: "admin", Authenticated: true})
+
+	tests := []struct {
+		name    string
+		ctx     context.Context
+		perm    os.FileMode
+		wantErr bool
+	}{
+		{"a", admin, 0700, false},
+		{"/a/", admin, 0700, true}, // already exists
+		{"ab/c\x00d/ef", admin, 0700, true},
+		{"/a/a/a/a", admin, 0700, true},
+		{"a/a/a/a", admin, 0700, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			d := Dir{
+				Config: configTmp,
+			}
+			if err := d.Mkdir(admin, tt.name, tt.perm); (err != nil) != tt.wantErr {
+				t.Errorf("Dir.Mkdir() name = %v, error = %v, wantErr %v", tt.name, err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func createTestConfig(dir string) *Config {
+	subdirs := [2]string{"subdir1", "subdir2"}
+	userInfos := map[string]*UserInfo{
+		"admin": {},
+		"user1": {
+			Subdir: &subdirs[0],
+		},
+		"user2": {
+			Subdir: &subdirs[1],
+		},
+	}
+	config := &Config{
+		Dir:   dir,
+		Users: userInfos,
+		Log: Logging{
+			Error:  true,
+			Create: true,
+			Read:   true,
+			Update: true,
+			Delete: true,
+		},
+	}
+	return config
+}