Add String.prototype.split test

test/annexB/built-ins/String/prototype/split/custom-splitter-emulates-undefined.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-string.prototype.split
+description: >
+  [[IsHTMLDDA]] object as @@split method gets called.
+info: |
+  String.prototype.split ( separator, limit )
+
+  [...]
+  2. If separator is neither undefined nor null, then
+    a. Let splitter be ? GetMethod(separator, @@split).
+    b. If splitter is not undefined, then
+      i. Return ? Call(splitter, separator, « O, limit »).
+features: [Symbol.split, IsHTMLDDA]
+---*/
+
+var separator = $262.IsHTMLDDA;
+var splitterGets = 0;
+Object.defineProperty(separator, Symbol.split, {
+  get: function() {
+    splitterGets += 1;
+    return separator;
+  },
+  configurable: true,
+});
+
+assert.sameValue("".split(separator), null);
+assert.sameValue(splitterGets, 1);