testing/slogtest: test nested groups

Updates #62280

src/testing/slogtest/slogtest.go

@@ -171,6 +171,22 @@ var cases = []testCase{
 			inGroup("G", missingKey("H")),
 		},
 	},
+	{
+		name:        "with-group-record-nested",
+		explanation: withSource("a Handler should not output nested groups if there are no attributes"),
+		f: func(l *slog.Logger) {
+			l.With("a", "b").WithGroup("G").With("c", "d").WithGroup("H").WithGroup("I").Info("msg")
+		},
+		checks: []check{
+			hasKey(slog.TimeKey),
+			hasKey(slog.LevelKey),
+			hasAttr(slog.MessageKey, "msg"),
+			hasAttr("a", "b"),
+			inGroup("G", hasAttr("c", "d")),
+			inGroup("G", missingKey("H")),
+			inGroup("G", missingKey("I")),
+		},
+	},
 	{
 		name:        "resolve",
 		explanation: withSource("a Handler should call Resolve on attribute values"),