test: polyfill Promise.allSettled for Node.js <12

test/sandbox-coverage.js

@@ -13,3 +13,21 @@ sandbox.configure({
     },
   },
 });
+
+// polyfill for Node.js <12
+Promise.allSettled =
+  Promise.allSettled ||
+  ((promises) =>
+    Promise.all(
+      promises.map((p) =>
+        p
+          .then((value) => ({
+            status: 'fulfilled',
+            value,
+          }))
+          .catch((reason) => ({
+            status: 'rejected',
+            reason,
+          }))
+      )
+    ));