diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-done.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-done.js
new file mode 100644
index 0000000000..58dd2b6e32
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-done.js
@@ -0,0 +1,52 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: next() will reject promise if getter `done` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let nextResult be IteratorNext(syncIteratorRecord, value).
+  6. IfAbruptRejectPromise(nextResult, promiseCapability).
+  7. Let nextDone be IteratorComplete(nextResult).
+  8. IfAbruptRejectPromise(nextDone, promiseCapability).
+  ...
+  18. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return {
+	  get done() {
+	    throw thrownError;
+	  },
+	  value: 1
+	}
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+asyncg().next().then(
+  function (result) {
+    throw new Test262Error("Promise should be rejected.");
+  },
+  function (err) {
+    assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+  }
+).then($DONE, $DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-value.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-value.js
new file mode 100644
index 0000000000..ba76169daf
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-poisoned-value.js
@@ -0,0 +1,54 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: next() will reject promise if getter `value` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let nextResult be IteratorNext(syncIteratorRecord, value).
+  6. IfAbruptRejectPromise(nextResult, promiseCapability).
+  7. Let nextDone be IteratorComplete(nextResult).
+  8. If AbruptRejectPromise(nextDone, promiseCapability).
+  9. Let nextValue be IteratorValue(nextResult).
+  10. IfAbruptRejectPromise(nextValue, promiseCapability).
+  ...
+  18. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return {
+	  get value() {
+	    throw thrownError;
+	  },
+	  done: false
+	}
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+asyncg().next().then(
+  function (result) {
+    throw new Test262Error("Promise should be rejected.");
+  },
+  function (err) {
+    assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+  }
+).then($DONE, $DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-prototype.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-prototype.js
new file mode 100644
index 0000000000..06ebc60d80
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-prototype.js
@@ -0,0 +1,42 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: next() returns a promise for an IteratorResult object
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let nextResult be IteratorNext(syncIteratorRecord, value).
+  6. IfAbruptRejectPromise(nextResult, promiseCapability).
+  7. Let nextDone be IteratorComplete(nextResult).
+  8. If AbruptRejectPromise(nextDone, promiseCapability).
+  9. Let nextValue be IteratorValue(nextResult).
+  10. IfAbruptRejectPromise(nextValue, promiseCapability).
+  ...
+  14. Let steps be the algorithm steps defined in Async-from-Sync Iterator Value Unwrap Functions.
+
+  Async-from-Sync Iterator Value Unwrap Functions
+  1. Return ! CreateIterResultObject(value, F.[[Done]]).
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+function* g() {}
+
+async function* asyncg() {
+  yield* g();
+}
+
+asyncg().next().then(function (result) {
+  assert(
+    Object.hasOwnProperty.call(result, 'value'), 'Has "own" property `value`'
+  );
+  assert(
+    Object.hasOwnProperty.call(result, 'done'), 'Has "own" property `done`'
+  );
+  assert.sameValue(Object.getPrototypeOf(result), Object.prototype);
+}).then($DONE, $DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-rejected.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-rejected.js
new file mode 100644
index 0000000000..2aa943188d
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-rejected.js
@@ -0,0 +1,43 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: next() will reject promise if sync iterator next() function returns an aburpt completion
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let nextResult be IteratorNext(syncIteratorRecord, value).
+  6. IfAbruptRejectPromise(nextResult, promiseCapability).
+  7. Let nextDone be IteratorComplete(nextResult).
+  8. If AbruptRejectPromise(nextDone, promiseCapability).
+  9. Let nextValue be IteratorValue(nextResult).
+  10. IfAbruptRejectPromise(nextValue, promiseCapability).
+  ...
+  18. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+function* g() {
+  throw thrownError;
+}
+
+async function* asyncg() {
+  yield* g();
+}
+
+asyncg().next().then(
+  function (result) {
+    throw new Test262Error("Promise should be rejected.");
+  },
+  function (err) {
+    assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+  }
+).then($DONE, $DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-unwrap-promise.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-unwrap-promise.js
new file mode 100644
index 0000000000..d3ccdcaebc
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/iterator-result-unwrap-promise.js
@@ -0,0 +1,43 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: next() will unwrap a Promise value return by the sync iterator
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let nextResult be IteratorNext(syncIteratorRecord, value).
+  6. IfAbruptRejectPromise(nextResult, promiseCapability).
+  7. Let nextDone be IteratorComplete(nextResult).
+  8. If AbruptRejectPromise(nextDone, promiseCapability).
+  9. Let nextValue be IteratorValue(nextResult).
+  10. IfAbruptRejectPromise(nextValue, promiseCapability).
+  ...
+  14. Let steps be the algorithm steps defined in Async-from-Sync Iterator Value Unwrap Functions.
+
+  Async-from-Sync Iterator Value Unwrap Functions
+  An async-from-sync iterator value unwrap function is an anonymous built-in
+  function that is used by methods of %AsyncFromSyncIteratorPrototype% when
+  processing the value field of an IteratorResult object, in order to wait for
+  its value if it is a promise and re-package the result in a new "unwrapped"
+  IteratorResult object. Each async iterator value unwrap function has a
+  [[Done]] internal slot.
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+function* g() {
+  yield Promise.resolve(1);
+}
+
+async function* asyncg() {
+  yield* g();
+}
+
+asyncg().next().then(function (result) {
+  assert.sameValue(result.value, 1, "result.value should be unwrapped promise, got: " + result.value)
+}).then($DONE, $DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/next/return-promise.js b/test/built-ins/AsyncFromSyncIteratorPrototype/next/return-promise.js
new file mode 100644
index 0000000000..d3bb1be2f4
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/next/return-promise.js
@@ -0,0 +1,27 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.next
+description: >
+  "next" returns a promise for an IteratorResult object
+info: |
+  %AsyncFromSyncIteratorPrototype%.next ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  18. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+function* g() {
+}
+
+async function* asyncg() {
+  yield* g();
+}
+
+var result = asyncg().next();
+assert(result instanceof Promise)
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-done.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-done.js
new file mode 100644
index 0000000000..e3c4c09b65
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-done.js
@@ -0,0 +1,70 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will reject promise if getter `done` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  ...
+  8. Let returnResult be Call(return, syncIterator, « value »).
+  9. IfAbruptRejectPromise(returnResult, promiseCapability).
+  ...
+  11. Let returnDone be IteratorComplete(returnResult).
+  12. IfAbruptRejectPromise(returnDone, promiseCapability).
+  13. Let returnValue be IteratorValue(returnResult).
+  14. IfAbruptRejectPromise(returnValue, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      return() {
+	return {
+	  get done() {
+	    throw thrownError;
+	  },
+	  value: 1
+	}
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-value.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-value.js
new file mode 100644
index 0000000000..181d8aa99f
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-poisoned-value.js
@@ -0,0 +1,70 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will reject promise if getter `value` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  ...
+  8. Let returnResult be Call(return, syncIterator, « value »).
+  9. IfAbruptRejectPromise(returnResult, promiseCapability).
+  ...
+  11. Let returnDone be IteratorComplete(returnResult).
+  12. IfAbruptRejectPromise(returnDone, promiseCapability).
+  13. Let returnValue be IteratorValue(returnResult).
+  14. IfAbruptRejectPromise(returnValue, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+
+var thrownError = new Error("Catch me.");
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      return() {
+	return {
+	  get value() {
+	    throw thrownError;
+	  },
+	  done: false
+	}
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-unwrap-promise.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-unwrap-promise.js
new file mode 100644
index 0000000000..08ed58ec30
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result-unwrap-promise.js
@@ -0,0 +1,63 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will unwrap a Promise value return by the sync iterator
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  ...
+  17. Let steps be the algorithm steps defined in Async-from-Sync Iterator Value Unwrap Functions.
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+  Async-from-Sync Iterator Value Unwrap Functions
+  An async-from-sync iterator value unwrap function is an anonymous built-in
+  function that is used by methods of %AsyncFromSyncIteratorPrototype% when
+  processing the value field of an IteratorResult object, in order to wait for
+  its value if it is a promise and re-package the result in a new "unwrapped"
+  IteratorResult object. Each async iterator value unwrap function has a
+  [[Done]] internal slot.
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      return() {
+	return {
+	  value: Promise.resolve(42),
+	  done: true
+	};
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+let iter = asyncg();
+
+iter.next().then(function (result) {
+  iter.return().then(
+    function (result) {
+      assert.sameValue(result.value, 42, "Result.value should be unwrapped, got: " + result.value);
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+}).then($DONE, $DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result.js
new file mode 100644
index 0000000000..9b4cbd2c0c
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/iterator-result.js
@@ -0,0 +1,55 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will return a iterator result object when built-in sync throw is called
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  ...
+  8. Let returnResult be Call(return, syncIterator, « value »).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+  Generator.prototype.return ( value )
+  1. Let g be the this value.
+  2. Let C be Completion{[[Type]]: return, [[Value]]: value, [[Target]]: empty}.
+  3. Return ? GeneratorResumeAbrupt(g, C).
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+function* g() {
+  yield 42;
+  throw new Test262Error('return closes iter');
+  yield 43;
+}
+
+async function* asyncg() {
+  yield* g();
+}
+
+var iter = asyncg();
+var val = 'some specific return value'
+
+iter.next().then(function(result) {
+
+  // return will call sync generator prototype built-in function return
+  iter.return(val).then(function(result) {
+
+    assert.sameValue(result.done, true, 'the iterator is completed');
+    assert.sameValue(result.value, val, 'expect agrument to `return`');
+
+    iter.next().then(({ done, value }) => {
+      assert.sameValue(done, true, 'the iterator is completed');
+      assert.sameValue(value, undefined, 'value is undefined');
+    }).then($DONE, $DONE);
+
+  }).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-get-return.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-get-return.js
new file mode 100644
index 0000000000..01dd66eb4a
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-get-return.js
@@ -0,0 +1,59 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will return rejected promise if getter of `return` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  6. IfAbruptRejectPromise(return, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      get return() {
+	throw thrownError;
+      }
+    }
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-return.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-return.js
new file mode 100644
index 0000000000..4616739ce1
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/poisoned-return.js
@@ -0,0 +1,65 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will return rejected promise if getter of `return` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  6. IfAbruptRejectPromise(return, promiseCapability).
+  ...
+  8. Let returnResult be Call(return, syncIterator, « value »).
+  ...
+  10. If Type(returnResult) is not Object,
+    a. Perform ! Call(promiseCapability.[[Reject]], undefined, « a TypeError exception »).
+    b. Return promiseCapability.[[Promise]].
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      return() {
+	throw thrownError;
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/result-object-error.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/result-object-error.js
new file mode 100644
index 0000000000..9014adafbe
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/result-object-error.js
@@ -0,0 +1,64 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.return
+description: return() will return rejected promise if getter of `return` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  6. IfAbruptRejectPromise(return, promiseCapability).
+  ...
+  8. Let returnResult be Call(return, syncIterator, « value »).
+  ...
+  10. If Type(returnResult) is not Object,
+    a. Perform ! Call(promiseCapability.[[Reject]], undefined, « a TypeError exception »).
+    b. Return promiseCapability.[[Promise]].
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      return() {
+	return 1;
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      let typeerror = err instanceof TypeError;
+      assert(typeerror, "Expect TypeError, got: " + err);
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/return/return-undefined.js b/test/built-ins/AsyncFromSyncIteratorPrototype/return/return-undefined.js
new file mode 100644
index 0000000000..5e7243eae7
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/return/return-undefined.js
@@ -0,0 +1,54 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: return() will return value undefined if sync `return` is undefined
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "return").
+  6. IfAbruptRejectPromise(return, promiseCapability).
+  7. If return is undefined, then
+    a. Let iterResult be ! CreateIterResultObject(value, true).
+    b. Perform ! Call(promiseCapability.[[Resolve]], undefined, « iterResult »).
+    c. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.return().then(function(result) {
+
+    assert.sameValue(result.done, true, 'the iterator is completed');
+    assert.sameValue(result.value, undefined, 'expect value to be undefined');
+
+    iter.next().then(({ done, value }) => {
+      assert.sameValue(done, true, 'the iterator is completed');
+      assert.sameValue(value, undefined, 'value is undefined');
+    }).then($DONE, $DONE);
+
+  }).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-done.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-done.js
new file mode 100644
index 0000000000..0bae74492e
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-done.js
@@ -0,0 +1,69 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will reject promise if getter `done` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  ...
+  8. Let throwResult be Call(throw, syncIterator, « value »).
+  ...
+  11. Let throwDone be IteratorComplete(throwResult).
+  12. IfAbruptRejectPromise(throwDone, promiseCapability).
+  13. Let throwValue be IteratorValue(throwResult).
+  14. IfAbruptRejectPromise(throwValue, promiseCapability).
+  ...
+  20. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      throw() {
+	return {
+	  get done() {
+	    throw thrownError;
+	  },
+	  value: 1
+	}
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-value.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-value.js
new file mode 100644
index 0000000000..a04f988a2d
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-poisoned-value.js
@@ -0,0 +1,69 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will reject promise if getter `value` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  ...
+  8. Let throwResult be Call(throw, syncIterator, « value »).
+  ...
+  11. Let throwDone be IteratorComplete(throwResult).
+  12. IfAbruptRejectPromise(throwDone, promiseCapability).
+  13. Let throwValue be IteratorValue(throwResult).
+  14. IfAbruptRejectPromise(throwValue, promiseCapability).
+  ...
+  20. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      throw() {
+	return {
+	  get value() {
+	    throw thrownError;
+	  },
+	  done: false
+	}
+      }
+    }
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-unwrap-promise.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-unwrap-promise.js
new file mode 100644
index 0000000000..521f513111
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result-unwrap-promise.js
@@ -0,0 +1,65 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will unwrap a Promise value return by the sync iterator
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  ...
+  17. Let steps be the algorithm steps defined in Async-from-Sync Iterator Value Unwrap Functions.
+  ...
+  20. Return promiseCapability.[[Promise]].
+
+  Async-from-Sync Iterator Value Unwrap Functions
+  An async-from-sync iterator value unwrap function is an anonymous built-in
+  function that is used by methods of %AsyncFromSyncIteratorPrototype% when
+  processing the value field of an IteratorResult object, in order to wait for
+  its value if it is a promise and re-package the result in a new "unwrapped"
+  IteratorResult object. Each async iterator value unwrap function has a
+  [[Done]] internal slot.
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Don't catch me.")
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      throw() {
+	return {
+	  value: Promise.resolve(42),
+	  done: true
+	};
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+let iter = asyncg();
+
+iter.next().then(function (result) {
+  iter.throw(thrownError).then(
+    function (result) {
+      assert.sameValue(result.value, 42, "Result.value should be unwrapped, got: " + result.value);
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+}).then($DONE, $DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result.js
new file mode 100644
index 0000000000..041ca20099
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/iterator-result.js
@@ -0,0 +1,59 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will call default sync throw
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  ...
+  8. Let throwResult be Call(throw, syncIterator, « value »)
+  9. IfAbruptRejectPromise(throwResult, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+  Generator.prototype.throw ( exception )
+  1. Let g be the this value.
+  2. Let C be Completion{[[Type]]: throw, [[Value]]: exception, [[Target]]: empty}.
+  3. Return ? GeneratorResumeAbrupt(g, C).
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.")
+
+function* g() {
+  yield 42;
+  throw new Test262Error('throw closes iter');
+  yield 43;
+}
+
+async function* asyncg() {
+  yield* g();
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  // throw will call sync generator prototype built-in function throw
+  iter.throw(thrownError).then(
+    function(result) {
+      throw new Test262Error('throw should cause rejection of promise');
+    },
+    function(err) {
+      assert.sameValue(err, thrownError, "promise should be reject with custom error, got: " + err)
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-get-throw.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-get-throw.js
new file mode 100644
index 0000000000..87609bebbb
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-get-throw.js
@@ -0,0 +1,59 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will return rejected promise if getter of `throw` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.return ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "throw").
+  6. IfAbruptRejectPromise(throw, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      get throw() {
+	throw thrownError;
+      }
+    }
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-throw.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-throw.js
new file mode 100644
index 0000000000..25bfc5b286
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/poisoned-throw.js
@@ -0,0 +1,61 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will return rejected promise if getter of `throw` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  6. IfAbruptRejectPromise(throw, promiseCapability).
+  ...
+  8. Let throwResult be Call(throw, syncIterator, « value »).
+  9. IfAbruptRejectPromise(throwResult, promiseCapability).
+  ...
+  22. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Catch me.");
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      throw() {
+	throw thrownError;
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, thrownError, "Promise should be rejected with thrown error");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/result-object-error.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/result-object-error.js
new file mode 100644
index 0000000000..35e9f8336f
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/result-object-error.js
@@ -0,0 +1,64 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will return rejected promise if getter of `throw` abrupt completes
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let throw be GetMethod(syncIterator, "throw").
+  6. IfAbruptRejectPromise(thow, promiseCapability).
+  ...
+  8. Let throwResult be Call(throw, syncIterator, « value »).
+  ...
+  10. If Type(throwResult) is not Object,
+    a. Perform ! Call(promiseCapability.[[Reject]], undefined, « a TypeError exception »).
+    b. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var thrownError = new Error("Don't catch me.")
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      },
+      throw() {
+	return 1;
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw(thrownError).then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      let typeerror = err instanceof TypeError;
+      assert(typeerror, "Expect TypeError, got: " + err);
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+
diff --git a/test/built-ins/AsyncFromSyncIteratorPrototype/throw/throw-undefined.js b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/throw-undefined.js
new file mode 100644
index 0000000000..94863e2c5a
--- /dev/null
+++ b/test/built-ins/AsyncFromSyncIteratorPrototype/throw/throw-undefined.js
@@ -0,0 +1,55 @@
+// Copyright (C) 2018 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%asyncfromsynciteratorprototype%.throw
+description: throw() will return rejected promise if sync `throw` undefined
+info: |
+  %AsyncFromSyncIteratorPrototype%.throw ( value )
+  ...
+  2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  ...
+  5. Let return be GetMethod(syncIterator, "throw").
+  6. IfAbruptRejectPromise(throw, promiseCapability).
+  7. If throw is undefined, then
+    a. Perform ! Call(promiseCapability.[[Reject]], undefined, « value »).
+    b. Return promiseCapability.[[Promise]].
+
+flags: [async]
+features: [async-iteration]
+---*/
+
+var obj = {
+  [Symbol.iterator]() {
+    return {
+      next() {
+	return { value: 1, done: false };
+      }
+    };
+  }
+};
+
+async function* asyncg() {
+  yield* obj;
+}
+
+var iter = asyncg();
+
+iter.next().then(function(result) {
+
+  iter.throw().then(
+    function (result) {
+      throw new Test262Error("Promise should be rejected, got: " + result.value);
+    },
+    function (err) {
+      assert.sameValue(err, undefined, "Promise should be rejected with undefined");
+
+      iter.next().then(({ done, value }) => {
+	assert.sameValue(done, true, 'the iterator is completed');
+	assert.sameValue(value, undefined, 'value is undefined');
+      }).then($DONE, $DONE);
+    }
+  ).catch($DONE);
+
+}).catch($DONE);
+