Add test that only explicit undefined return value is awaited in async generator

test/language/statements/async-generator/return-undefined-implicit-and-explicit.js

@@ -0,0 +1,80 @@
+// Copyright (C) 2019 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-return-statement-runtime-semantics-evaluation
+description: >
+  Return with an explicit return value awaits this value.
+info: |
+  13.10.1 Runtime Semantics: Evaluation
+
+    ReturnStatement : return;
+      1. Return Completion { [[Type]]: return, [[Value]]: undefined, [[Target]]: empty }.
+
+    ReturnStatement : return Expression ;
+      1. Let exprRef be the result of evaluating Expression.
+      2. Let exprValue be ? GetValue(exprRef).
+      3. If ! GetGeneratorKind() is async, set exprValue to ? Await(exprValue).
+      4. Return Completion { [[Type]]: return, [[Value]]: exprValue, [[Target]]: empty }.
+
+  25.5.3.2 AsyncGeneratorStart ( generator, generatorBody )
+
+    ...
+    5. Set the code evaluation state of genContext such that when evaluation is resumed for that
+       execution context the following steps will be performed:
+      a. Let result be the result of evaluating generatorBody.
+      ...
+      e. If result is a normal completion, let resultValue be undefined.
+      ...
+      g. Return ! AsyncGeneratorResolve(generator, resultValue, true).
+
+includes: [compareArray.js]
+flags: [async]
+features: [async-iteration]
+---*/
+
+// 25.5.3.2, step 5.e: |generatorBody| execution ends with a normal completion.
+async function* g1() {
+  // no return
+}
+
+// 13.10.1: No expression form means direct return.
+async function* g2() {
+  return;
+}
+
+// 13.10.1: Explicit expression requires Await.
+async function* g3() {
+  return undefined; // Return undefined via global value `undefined`.
+}
+
+// 13.10.1: Explicit expression requires Await.
+async function* g4() {
+  return void 0; // Return undefined via void expression.
+}
+
+var expected = [
+  "tick 1",
+
+  "g1 ret",
+  "g2 ret",
+
+  "tick 2",
+
+  "g3 ret",
+  "g4 ret",
+];
+
+var actual = [];
+
+Promise.resolve(0)
+  .then(() => actual.push("tick 1"))
+  .then(() => actual.push("tick 2"))
+  .then(() => {
+    assert.compareArray(actual, expected, "Ticks for implicit and explicit return undefined");
+}).then($DONE, $DONE);
+
+g1().next().then(v => actual.push("g1 ret"));
+g2().next().then(v => actual.push("g2 ret"));
+g3().next().then(v => actual.push("g3 ret"));
+g4().next().then(v => actual.push("g4 ret"));