if cli -f is a dir, then edit each file+clean each file+keep each as individual file

cmd/pttodo-cli/cli_test.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"strconv"
+	"testing"
+)
+
+func TestListDir(t *testing.T) {
+	d := t.TempDir()
+	want := []string{}
+	for i := 0; i < 3; i++ {
+		p := path.Join(d, strconv.Itoa(i))
+		ioutil.WriteFile(p, []byte{}, os.ModePerm)
+		want = append(want, p)
+	}
+	os.Mkdir(path.Join(d, "d"), os.ModePerm)
+
+	got, err := listDir(d)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if fmt.Sprint(want) != fmt.Sprint(got) {
+		t.Fatal(want, got)
+	}
+}