test/language/expressions: Add nullish coalescing tests

Copies a few tests for nullish coalescing straight from the newest
test262 master branch so that we can test
https://codereview.qt-project.org/c/qt/qtdeclarative/+/283241 .

Change-Id: I312e96c1e2934d2933421371d58bfce670f244ae
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 26 insertions, 0 deletions

diff --git a/test/language/expressions/coalesce/tco-pos-undefined.js b/test/language/expressions/coalesce/tco-pos-undefined.js
new file mode 100644
index 000000000..0065123eb
--- /dev/null
+++ b/test/language/expressions/coalesce/tco-pos-undefined.js
@@ -0,0 +1,26 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Expression is a candidate for tail-call optimization.
+esid: sec-static-semantics-hascallintailposition
+info: |
+  Expression Rules
+
+  CoalesceExpression : CoalesceExpressionHead ?? BitwiseORExpression
+
+  1. Return HasCallInTailPosition of BitwiseORExpression with argument call.
+flags: [onlyStrict]
+features: [tail-call-optimization, coalesce-expression]
+includes: [tcoHelper.js]
+---*/
+
+var callCount = 0;
+(function f(n) {
+  if (n === 0) {
+    callCount += 1
+    return;
+  }
+  return undefined ?? f(n - 1);
+}($MAX_ITERATIONS));
+assert.sameValue(callCount, 1);