Add String.prototype.split test

test/built-ins/String/prototype/split/cstm-split-is-null.js

@@ -0,0 +1,34 @@
+// 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: >
+  If separator's Symbol.split property is null, no error is thrown.
+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
+      [...]
+  [...]
+  17. Return A.
+
+  GetMethod ( V, P )
+
+  [...]
+  2. Let func be ? GetV(V, P).
+  3. If func is either undefined or null, return undefined.
+includes: [compareArray.js]
+features: [Symbol.split]
+---*/
+
+var separator = {};
+separator[Symbol.split] = null;
+separator.toString = function() { return "2"; };
+separator.valueOf = function() { throw new Test262Error("should not be called"); };
+
+assert.compareArray("a2b2c".split(separator), ["a", "b", "c"]);
+assert.compareArray("a2b2c".split(separator, 1), ["a"]);