Add "lastIndex" init test

test/built-ins/RegExp/prototype/Symbol.search/set-lastindex-init-samevalue.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-regexp.prototype-@@search
+description: >
+  `previousLastIndex` value is compared using SameValue. 
+info: |
+  RegExp.prototype [ @@search ] ( string )
+
+  [...]
+  4. Let previousLastIndex be ? Get(rx, "lastIndex").
+  5. If SameValue(previousLastIndex, 0) is false, then
+    a. Perform ? Set(rx, "lastIndex", 0, true).
+  6. Let result be ? RegExpExec(rx, S).
+  [...]
+features: [Symbol.search]
+---*/
+
+var re = /(?:)/;
+var execLastIndex;
+
+re.lastIndex = -0;
+re.exec = function() {
+  execLastIndex = re.lastIndex;
+  return null;
+};
+
+assert.sameValue(re[Symbol.search](""), -1);
+assert.sameValue(execLastIndex, 0);