add test for tc39/proposal-iterator-sequencing#19 (#4485)

test/built-ins/Iterator/concat/get-value-after-done.js

@@ -0,0 +1,47 @@
+// Copyright (C) 2025 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator.concat
+description: >
+  Iterator.concat accesses the value of a done IteratorResult, matching the behaviour of yield*
+info: |
+  Iterator.concat ( ...items )
+
+  ...
+  3. Let closure be a new Abstract Closure with no parameters that captures iterables and performs the following steps when called:
+    a. For each Record iterable of iterables, do
+      ...
+      v. Repeat, while innerAlive is true,
+        1. Let iteratorResult be ? IteratorNext(iteratorRecord).
+        2. Let done be Completion(IteratorComplete(iteratorResult)).
+        3. If done is a throw completion, then
+          a. Set iteratorRecord.[[Done]] to true.
+          b. Return ? done.
+        4. Set done to ! done.
+        5. If done is true, then
+          a. Set iteratorRecord.[[Done]] to true.
+          b. Perform ? IteratorValue(iteratorResult).
+          ...
+features: [iterator-sequencing]
+---*/
+
+let valueAccesses = 0;
+let iter = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+        return {
+          get value() {
+            ++valueAccesses;
+          },
+          done: true,
+        };
+      },
+    };
+  }
+};
+
+Array.from(Iterator.concat(iter, iter, iter));
+
+assert.sameValue(valueAccesses, 3, 'Iterator.concat also accesses value getter after each iterator is done');