Test limits in PlainDate#toPlainYearMonth.

test/built-ins/Temporal/PlainDate/prototype/toPlainYearMonth/limits.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.toplainyearmonth
+description: toPlainYearMonth works within the supported range
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const min = Temporal.PlainDate.from('-271821-04-19');
+TemporalHelpers.assertPlainYearMonth(min.toPlainYearMonth(),
+  -271821, 4, "M04", "min");
+
+const max = Temporal.PlainDate.from('+275760-09-13');
+TemporalHelpers.assertPlainYearMonth(max.toPlainYearMonth(),
+  275760, 9, "M09", "max");