test pttodo.NewRootFromFile accepts both []Todo and Root

pttodo/root.go

@@ -1,6 +1,7 @@
 package pttodo
 
 import (
+	"bytes"
 	"os"
 
 	yaml "gopkg.in/yaml.v2"
@@ -13,6 +14,10 @@ type Root struct {
 }
 
 func NewRootFromFile(p string) (Root, error) {
+	if b, err := os.ReadFile(p); err == nil && len(bytes.TrimSpace(b)) == 0 {
+		return Root{}, nil
+	}
+
 	f, err := os.Open(p)
 	if os.IsNotExist(err) {
 		return Root{}, nil
@@ -24,7 +29,11 @@ func NewRootFromFile(p string) (Root, error) {
 
 	var result Root
 	if err := yaml.NewDecoder(f).Decode(&result); err != nil {
-		return Root{}, err
+		todos, err2 := NewTodosFromFile(p)
+		if err2 != nil {
+			return Root{}, err
+		}
+		result.Todo = todos
 	}
 
 	result.AutoMove()

pttodo/root_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"os"
+	"path"
 	"strconv"
 	"strings"
 	"testing"
@@ -180,3 +182,54 @@ done:
 		t.Fatalf("want\n\t%q, got\n\t%q", want, string(got))
 	}
 }
+
+func TestRootFromFile(t *testing.T) {
+	cases := map[string]struct {
+		given string
+		want  Root
+	}{
+		"empty": {},
+		"happy": {
+			given: `{"todo":["a", "b"],"scheduled":["c"], "done":[{"todo": "d"}]}`,
+			want: Root{
+				Todo: []Todo{
+					Todo{Todo: "a"},
+					Todo{Todo: "b"},
+				},
+				Scheduled: []Todo{
+					Todo{Todo: "c"},
+				},
+				Done: []Todo{
+					Todo{Todo: "d"},
+				},
+			},
+		},
+		"todos": {
+			given: `["a", {"todo": "b"}]`,
+			want: Root{
+				Todo: []Todo{
+					{Todo: "a"},
+					{Todo: "b"},
+				},
+			},
+		},
+	}
+
+	for name, d := range cases {
+		c := d
+		t.Run(name, func(t *testing.T) {
+			d := t.TempDir()
+			p := path.Join(d, "input.yaml")
+			if err := os.WriteFile(p, []byte(c.given), os.ModePerm); err != nil {
+				t.Fatal(err)
+			}
+			got, err := NewRootFromFile(p)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if fmt.Sprintf("%+v", got) != fmt.Sprintf("%+v", c.want) {
+				t.Errorf("want\n\t%+v, got\n\t%+v", c.want, got)
+			}
+		})
+	}
+}