test: add test for ?. [expression] edge cases (#2297)

test/language/expressions/optional-chaining/optional-chain-expression-optional-expression.js

@@ -0,0 +1,20 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  optional chain bracket notation containing optional expresion
+info: |
+  OptionalChain:
+    ?. [OptionalExpression]
+features: [optional-chaining]
+---*/
+const a = undefined;
+const b = {e: 0};
+const c = {};
+c[undefined] = 11;
+const d = [22];
+
+assert.sameValue(undefined, a?.[a?.b]);
+assert.sameValue(11, c?.[a?.b]);
+assert.sameValue(22, d?.[b?.e]);