add tests for `for ( async of`

test/language/statements/for-of/head-lhs-async-dot.js

@@ -0,0 +1,15 @@
+// Copyright (C) 2021 Kevin Gibbons. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: leading `async` token in for-of LHS
+info: |
+  The `async` token is allowed in the LHS if not followed by `of`
+esid: sec-for-in-and-for-of-statements
+---*/
+
+var async = { x: 0 };
+
+for (async.x of [1]) ;
+
+assert.sameValue(async.x, 1);

test/language/statements/for-of/head-lhs-async-invalid.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2021 Kevin Gibbons. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: leading `async` token in for-of LHS
+info: |
+  The `async` token is disallowed in the LHS when followed by `of`
+esid: sec-for-in-and-for-of-statements
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+$DONOTEVALUATE();
+
+var async;
+for (async of [1]) ;

test/language/statements/for/head-init-async-of.js

@@ -0,0 +1,16 @@
+// Copyright (C) 2021 Kevin Gibbons. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: for statement beginning with `async of`
+info: |
+  `for (async of =>` is the begining of a regular for loop, rather than a for-of
+esid: sec-for-statement
+---*/
+
+var i = 0;
+var counter = 0;
+for (async of => {}; i < 10; ++i) {
+  ++counter;
+}
+assert.sameValue(counter, 10);