Merge pull request #1443 from tc39/async-iteration-builtins

async-iteration: add tests for AsyncGenerationFunction and AsyncIteratorPrototype built-in

test/built-ins/AsyncGeneratorFunction/extensibility.js

@@ -0,0 +1,14 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-properties-of-asyncgeneratorfunction
+description: Object extensibility
+info: |
+  The value of the [[Extensible]] internal slot of the AsyncGeneratorFunction
+  constructor is true.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+assert(Object.isExtensible(AsyncGeneratorFunction));

test/built-ins/AsyncGeneratorFunction/has-instance.js

@@ -0,0 +1,34 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-properties-of-asyncgeneratorfunction
+description: >
+    AsyncGenerator function instances are correctly reported as instances of the
+    AsyncGeneratorFunction intrinsic.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+async function* agDecl() {}
+var agExpr = async function* () {};
+
+assert(
+  agDecl instanceof AsyncGeneratorFunction,
+  'AsyncGenerators created via AsyncGeneratorDeclaration syntax are proper instances of AsyncGeneratorFunction'
+);
+
+assert(
+  agExpr instanceof AsyncGeneratorFunction,
+  'AsyncGenerators created via AsyncGeneratorExpression syntax are proper instances of AsyncGeneratorFunction'
+);
+
+assert(
+  new AsyncGeneratorFunction() instanceof AsyncGeneratorFunction,
+  'AsyncGenerators created via constructor invocation of AsyncGeneratorFunction are proper instances of AsyncGeneratorFunction'
+);
+
+assert(
+  AsyncGeneratorFunction() instanceof AsyncGeneratorFunction,
+  'AsyncGenerators created via function invocation of AsyncGeneratorFunction are proper instances of AsyncGeneratorFunction'
+);

test/built-ins/AsyncGeneratorFunction/instance-await-expr-in-param.js

@@ -0,0 +1,42 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: Definition of instance `length` property
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    Runtime Semantics: CreateDynamicFunction
+    ...
+    29. If kind is "async" or "async generator", then
+        a. If parameters Contains AwaitExpression is true, throw a SyntaxError
+           exception.
+features: [async-iteration]
+flags: [async]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+// AwaitExpression is permitted in function body.
+AsyncGeneratorFunction('x = await 42');
+
+assert.throws(SyntaxError, function() {
+  AsyncGeneratorFunction('x = await 42', '');
+}, 'AwaitExpression not permitted in parameters');
+
+var withinAsyncGenerator = async function*() {
+  AsyncGeneratorFunction('x = await 42', '');
+};
+
+withinAsyncGenerator().next().then(
+ function () {
+   throw new Test262Error("AwaitExpression not permitted when calling context is a async generator");
+ },
+ function (e) {
+   if (!(e instanceof SyntaxError)) {
+    throw new Test262Error("Expected SyntaxError but got " + e);
+   }
+ }
+).then($DONE, $DONE);

test/built-ins/AsyncGeneratorFunction/instance-construct-throws.js

@@ -0,0 +1,31 @@
+// Copyright 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-asyncgeneratorfunction
+description: The instance created by AsyncGeneratorFunction is not a constructor
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return ? CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    Runtime Semantics: CreateDynamicFunction( constructor, newTarget, kind, args )
+    ...
+    32. Let F be FunctionAllocate(proto, strict, kind).
+    ...
+
+    FunctionAllocate ( functionPrototype, strict, functionKind )
+    // [[Construct]] and [[ConstructKind]] are not set for functionKind="async generators"
+
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var instance = AsyncGeneratorFunction();
+
+assert.throws(TypeError, function() {
+    new instance();
+})
+
+

test/built-ins/AsyncGeneratorFunction/instance-length.js

@@ -0,0 +1,45 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: Definition of instance `length` property
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    Runtime Semantics: CreateDynamicFunction
+    ...
+    // the parameter "args" is sliced into "parameters" and "body"
+    26. Perform FunctionInitialize(F, Normal, parameters, body, scope).
+    ...
+
+    FunctionInitialize
+    ...
+    2. Let len be the ExpectedArgumentCount of ParameterList.
+    3. Perform ! DefinePropertyOrThrow(F, "length",
+       PropertyDescriptor{[[Value]]: len, [[Writable]]: false, [[Enumerable]]:
+       false, [[Configurable]]: true}).
+    ...
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var instance = AsyncGeneratorFunction()
+
+verifyProperty(AsyncGeneratorFunction(), "length", {
+  value: 0,
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});
+
+assert.sameValue(AsyncGeneratorFunction('').length, 0, "test 1");
+assert.sameValue(AsyncGeneratorFunction('x').length, 0, "test 2");
+assert.sameValue(AsyncGeneratorFunction('x', '').length, 1, "test 3");
+assert.sameValue(AsyncGeneratorFunction('x', 'y', '').length, 2, "test 4");
+assert.sameValue(AsyncGeneratorFunction('x, y', '').length, 2, "test 5");
+
+

test/built-ins/AsyncGeneratorFunction/instance-name.js

@@ -0,0 +1,28 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-asyncgeneratorfunction
+description: Assignment of function `name` attribute
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    RuntimeSemantics: CreateDynamicFunction(constructor, newTarget, kind, args)
+    ...
+    29. Perform SetFunctionName(F, "anonymous").
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var instance = AsyncGeneratorFunction()
+
+verifyProperty(instance, "name", {
+  value: "anonymous",
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncGeneratorFunction/instance-prototype.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: Definition of instance `prototype` property
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    Runtime Semantics: CreateDynamicFunction
+    ...
+    37. Else if kind is "async generator", then
+        a. Let prototype be ObjectCreate(%AsyncGeneratorPrototype%).
+        b. Perform DefinePropertyOrThrow(F, "prototype",
+           PropertyDescriptor{[[Value]]: prototype, [[Writable]]: true,
+           [[Enumerable]]: false, [[Configurable]]: false}).
+    ...
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var instance = AsyncGeneratorFunction();
+
+assert.sameValue(typeof instance.prototype, 'object');
+assert.sameValue(
+  Object.getPrototypeOf(instance.prototype),
+  Object.getPrototypeOf(instance).prototype
+);
+
+verifyProperty(instance, "prototype", {
+  enumerable: false,
+  writable: true,
+  configurable: false,
+});

test/built-ins/AsyncGeneratorFunction/instance-yield-expr-in-param.js

@@ -0,0 +1,42 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: Definition of instance `length` property
+info: |
+    AsyncGeneratorFunction ( p1, p2, … , pn, body )
+    ...
+    3. Return CreateDynamicFunction(C, NewTarget, "async generator", args).
+
+    Runtime Semantics: CreateDynamicFunction
+    ...
+    28. If kind is "generator" or "async generator", then
+        a. If parameters Contains YieldExpression is true, throw a SyntaxError
+           exception.
+features: [async-iteration]
+flags: [async]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+// YieldExpression is permitted in function body.
+AsyncGeneratorFunction('x = yield');
+
+assert.throws(SyntaxError, function() {
+  AsyncGeneratorFunction('x = yield', '');
+}, 'YieldExpression not permitted generally');
+
+var withinAsyncGenerator = async function*() {
+  AsyncGeneratorFunction('x = yield', '');
+};
+
+withinAsyncGenerator().next().then(
+ function () {
+   throw new Test262Error("YieldExpression not permitted when calling context is a async generator");
+ },
+ function (e) {
+   if (!(e instanceof SyntaxError)) {
+    throw new Test262Error("Expected SyntaxError but got " + e);
+   }
+ }
+).then($DONE, $DONE);

test/built-ins/AsyncGeneratorFunction/invoked-as-constructor-no-arguments.js

@@ -0,0 +1,20 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: >
+    When invoked via the constructor invocation pattern without arguments, the
+    GeneratorFunction intrinsic returns a valid async generator with an empty body.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var g = new AsyncGeneratorFunction();
+var iter = g();
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Result `value`');
+  assert.sameValue(result.done, true, 'Result `done` flag');
+}).then($DONE, $DONE)
+

test/built-ins/AsyncGeneratorFunction/invoked-as-function-multiple-arguments.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: >
+    When invoked via the function invocation pattern with multiple arguments,
+    the AsyncGeneratorFunction intrinsic creates a valid generator whose body is the
+    last argument evaluated as source code and whose formal parameters are
+    defined by the preceeding arguments.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var g = AsyncGeneratorFunction('x', 'y', 'yield x + y;');
+var iter = g(2, 3);
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, 5, 'First result `value`');
+  assert.sameValue(result.done, false, 'First result `done` flag');
+}).then(undefined, $DONE)
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Final result `value`');
+  assert.sameValue(result.done, true, 'Final result `done` flag');
+}).then($DONE, $DONE)

test/built-ins/AsyncGeneratorFunction/invoked-as-function-no-arguments.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: >
+    When invoked via the function invocation pattern without arguments, the
+    AsyncGeneratorFunction intrinsic returns a valid generator with an empty body.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var g = AsyncGeneratorFunction();
+var iter = g();
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Result `value`');
+  assert.sameValue(result.done, true, 'Result `done` flag');
+}).then($DONE, $DONE)

test/built-ins/AsyncGeneratorFunction/invoked-as-function-single-argument.js

@@ -0,0 +1,28 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction
+description: >
+    When invoked via the function invocation pattern with a single argument,
+    the AsyncGeneratorFunction intrinsic creates a valid async generator whose body is the
+    first argument evaluated as source code.
+features: [async-iteration]
+flags: [async]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+var g = AsyncGeneratorFunction('yield 1;');
+var iter = g();
+var result;
+
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, 1, 'First result `value`');
+  assert.sameValue(result.done, false, 'First result `done` flag');
+}).then(undefined, $DONE)
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Final result `value`');
+  assert.sameValue(result.done, true, 'Final result `done` flag');
+}).then($DONE, $DONE)

test/built-ins/AsyncGeneratorFunction/length.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction-length
+description: >
+  This is a data property with a value of 1. This property has the attributes
+  { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+verifyProperty(AsyncGeneratorFunction, "length", {
+  value: 1,
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncGeneratorFunction/name.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-properties-of-asyncgeneratorfunction
+description: Function "name" property
+info: |
+  The value of the name property of the AsyncGeneratorFunction
+  is "AsyncGeneratorFunction".
+
+  17 ECMAScript Standard Built-in Objects:
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String.
+
+  Unless otherwise specified, the name property of a built-in Function object,
+  if it exists, has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+verifyProperty(AsyncGeneratorFunction, "name", {
+  value: "AsyncGeneratorFunction",
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncGeneratorFunction/prototype/Symbol.toStringTag.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-asyncgeneratorfunction-prototype-tostringtag
+description: >
+    `Symbol.toStringTag` property descriptor
+info: |
+  The initial value of the @@toStringTag property is the String
+  value "AsyncGeneratorFunction".
+
+  This property has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [async-iteration, Symbol.toStringTag]
+---*/
+
+var AsyncGeneratorFunctionPrototype = Object.getPrototypeOf(async function*() {});
+
+verifyProperty(AsyncGeneratorFunctionPrototype, Symbol.toStringTag, {
+  value: 'AsyncGeneratorFunction',
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncGeneratorFunction/prototype/constructor.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction-prototype-constructor
+description: >
+  `constructor` property of the AsyncGeneratorFunction.prototype object
+info: |
+  The initial value of AsyncGeneratorFunction.prototype.constructor is the intrinsic
+  object %AsyncGeneratorFunction%.
+
+  This property has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+assert.sameValue(AsyncGeneratorFunction.prototype.constructor, AsyncGeneratorFunction);
+
+verifyProperty(AsyncGeneratorFunction.prototype, "constructor", {
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncGeneratorFunction/prototype/extensibility.js

@@ -0,0 +1,14 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-properties-of-asyncgenerator-prototype
+description: Object extensibility
+info: |
+  The initial value of the [[Extensible]] internal slot of the
+  AsyncGeneratorFunction prototype object is true.
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+assert(Object.isExtensible(AsyncGeneratorFunction.prototype));

test/built-ins/AsyncGeneratorFunction/prototype/prop-desc.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: AsyncGeneratorFunction.prototype property descriptor
+esid: sec-asyncgeneratorfunction-prototype
+info: |
+  This property has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: false }.
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
+
+verifyProperty(AsyncGeneratorFunction, "prototype", {
+  enumerable: false,
+  writable: false,
+  configurable: false,
+});

test/built-ins/AsyncGeneratorFunction/prototype/prototype.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asyncgeneratorfunction-prototype-prototype
+description: >
+    The value of AsyncGeneratorFunction.prototype.prototype is the
+    %AsyncGeneratorPrototype% intrinsic object.
+
+    This property has the attributes { [[Writable]]: false,
+    [[Enumerable]]: false, [[Configurable]]: true }.
+includes: [propertyHelper.js]
+features: [async-iteration]
+---*/
+
+var AsyncGeneratorFunctionPrototype = Object.getPrototypeOf(async function*() {});
+
+assert.sameValue(
+  AsyncGeneratorFunctionPrototype.prototype,
+  Object.getPrototypeOf(async function*() {}.prototype)
+);
+
+verifyProperty(AsyncGeneratorFunctionPrototype, "prototype", {
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncIteratorPrototype/Symbol.asyncIterator/length.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asynciteratorprototype-asynciterator
+description: Length of AsyncIteratorPrototype[ @@asyncIterator ]
+info: |
+    ECMAScript Standard Built-in Objects
+    ...
+    Every built-in Function object, including constructors, has a length
+    property whose value is an integer. Unless otherwise specified, this value
+    is equal to the largest number of named arguments shown in the subclause
+    headings for the function description, including optional parameters.
+    ...
+    Unless otherwise specified, the length property of a built-in Function
+    object has the attributes { [[Writable]]: false, [[Enumerable]]: false,
+    [[Configurable]]: true }.
+features: [Symbol.asyncIterator, async-iteration]
+includes: [propertyHelper.js]
+---*/
+
+async function* generator() {}
+var AsyncIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf(generator.prototype))
+
+verifyProperty(AsyncIteratorPrototype[Symbol.asyncIterator], "length", {
+  value: 0,
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncIteratorPrototype/Symbol.asyncIterator/name.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asynciteratorprototype-asynciterator
+description: Descriptor for `name` property
+info: |
+  %AsyncIteratorPrototype% [ @@asyncIterator ] ( )
+  ...
+  The value of the name property of this function is "[Symbol.asyncIterator]".
+
+  ECMAScript Standard Built-in Objects
+  ...
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String. Unless otherwise specified, this value is the name that is given to
+  the function in this specification.
+  ...
+  Unless otherwise specified, the name property of a built-in Function
+  object, if it exists, has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+features: [Symbol.asyncIterator, async-iteration]
+includes: [propertyHelper.js]
+---*/
+
+async function* generator() {}
+var AsyncIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf(generator.prototype))
+
+verifyProperty(AsyncIteratorPrototype[Symbol.asyncIterator], "name", {
+  value: '[Symbol.asyncIterator]',
+  enumerable: false,
+  writable: false,
+  configurable: true,
+});

test/built-ins/AsyncIteratorPrototype/Symbol.asyncIterator/prop-desc.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asynciteratorprototype
+description: Property descriptor
+info: |
+    ECMAScript Standard Built-in Objects
+
+    Every other data property described in clauses 18 through 26 and in Annex
+    B.2 has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+    [[Configurable]]: true } unless otherwise specified.
+features: [Symbol.asyncIterator, async-iteration]
+includes: [propertyHelper.js]
+---*/
+
+async function* generator() {}
+var AsyncIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf(generator.prototype))
+
+assert.sameValue(typeof AsyncIteratorPrototype[Symbol.asyncIterator], 'function');
+
+verifyProperty(AsyncIteratorPrototype, Symbol.asyncIterator, {
+  enumerable: false,
+  writable: true,
+  configurable: true,
+});
+

test/built-ins/AsyncIteratorPrototype/Symbol.asyncIterator/return-val.js

@@ -0,0 +1,20 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-asynciteratorprototype-asynciterator
+description: Return value of @@asyncIterator
+info: |
+  %AsyncIteratorPrototype% [ @@asyncIterator ] ( )
+    1. Return the this value.
+features: [Symbol.asyncIterator, async-iteration]
+---*/
+
+async function* generator() {}
+var AsyncIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf(generator.prototype))
+
+var thisValue = {};
+
+assert.sameValue(
+  AsyncIteratorPrototype[Symbol.asyncIterator].call(thisValue),
+  thisValue
+);