generic: generalise json check

This code is shared for all json checks.

Signed-off-by: Yonah <contrib@gensokyo.uk>

albums_test.go

@@ -1,10 +1,7 @@
 package monstersirenfetch_test
 
 import (
-	"bytes"
 	_ "embed"
-	"encoding/json"
-	"reflect"
 	"testing"
 
 	. "git.gensokyo.uk/yonah/monstersirenfetch"
@@ -14,7 +11,7 @@ import (
 var albumsJSON []byte
 
 func TestAlbums(t *testing.T) {
-	want := Albums{Code: 0, Msg: "", Data: []Album{
+	checkJSONRoundTrip(t, Albums{Code: 0, Msg: "", Data: []Album{
 		{CID: 2444, Name: "无忧梦呓OST", CoverURL: "https://web.hycdn.cn/siren/pic/20250905/2039eb5cf7f7d3a951d5f653c6d33f64.jpg", Artists: []string{"塞壬唱片-MSR"}},
 		{CID: 5192, Name: "焰烬曙明OST", CoverURL: "https://web.hycdn.cn/siren/pic/20250905/6e32685dcc113791d9e90c14e18634c6.jpg", Artists: []string{"塞壬唱片-MSR"}},
 		{CID: 1019, Name: "in your blue eyes", CoverURL: "https://web.hycdn.cn/siren/pic/20250903/63d83dcec8698fde96edcd039d9f4fcf.jpg", Artists: []string{"Ave Mujica"}},
@@ -261,31 +258,5 @@ func TestAlbums(t *testing.T) {
 		{CID: 1030, Name: "Speed of Light", CoverURL: "https://web.hycdn.cn/siren/pic/20210322/56cbcd1d0093d8ee8ee22bf6d68ab4a6.jpg", Artists: []string{"塞壬唱片-MSR", "DJ Okawari"}},
 		{CID: 8947, Name: "火蓝之心原声带", CoverURL: "https://web.hycdn.cn/siren/pic/20210322/199df150e1370a4138fa0352ff95a5b5.jpg", Artists: []string{"Alive Until Sunset", " Emperor", " D.D.D."}},
 		{CID: 4527, Name: "明日方舟OST1", CoverURL: "https://web.hycdn.cn/siren/pic/20210322/bb51040a1dfe53b97590451156852bd6.jpg", Artists: []string{"塞壬唱片-MSR"}},
-	}}
+	}}, albumsJSON)
-
-	t.Run("marshal", func(t *testing.T) {
-		buf := new(bytes.Buffer)
-		buf.Grow(len(albumsJSON))
-		e := json.NewEncoder(buf)
-		// to match upstream behaviour
-		e.SetEscapeHTML(false)
-		err := e.Encode(&want)
-		if err != nil {
-			t.Fatalf("Marshal: error = %v", err)
-		}
-		got := bytes.TrimSuffix(buf.Bytes(), []byte{'\n'})
-		if string(got) != string(albumsJSON) {
-			t.Errorf("Marshal:\n%s\nwant\n%s", buf, string(albumsJSON))
-		}
-	})
-
-	t.Run("unmarshal", func(t *testing.T) {
-		var got Albums
-		if err := json.Unmarshal(albumsJSON, &got); err != nil {
-			t.Fatalf("Unmarshal: error = %v", err)
-		}
-		if !reflect.DeepEqual(&got, &want) {
-			t.Errorf("Unmarshal:\n%#v\nwant\n%#v", got, want)
-		}
-	})
 }

generic_test.go

@@ -1,6 +1,7 @@
 package monstersirenfetch_test
 
 import (
+	"bytes"
 	"encoding/json"
 	"reflect"
 	"strconv"
@@ -59,3 +60,31 @@ func newSyntaxError(msg string, offset int64) *json.SyntaxError {
 	reflect.NewAt(msgV.Type(), unsafe.Pointer(msgV.UnsafeAddr())).Elem().SetString(msg)
 	return e
 }
+
+func checkJSONRoundTrip[T any](t *testing.T, v T, data []byte) {
+	t.Run("marshal", func(t *testing.T) {
+		buf := new(bytes.Buffer)
+		buf.Grow(len(data))
+		e := json.NewEncoder(buf)
+		// to match upstream behaviour
+		e.SetEscapeHTML(false)
+		err := e.Encode(&v)
+		if err != nil {
+			t.Fatalf("Marshal: error = %v", err)
+		}
+		got := buf.Bytes()[:buf.Len()-1]
+		if string(got) != string(data) {
+			t.Errorf("Marshal:\n%s\nwant\n%s", string(got), string(data))
+		}
+	})
+
+	t.Run("unmarshal", func(t *testing.T) {
+		var got T
+		if err := json.Unmarshal(data, &got); err != nil {
+			t.Fatalf("Unmarshal: error = %v", err)
+		}
+		if !reflect.DeepEqual(&got, &v) {
+			t.Errorf("Unmarshal:\n%#v\nwant\n%#v", got, v)
+		}
+	})
+}