Increase branch coverage: Array.prototype functions (#2796)

Added new test cases to improve branch coverage in Array.prototype routines.

The following script is made for testing branch coverage with all the test suites (--jerry-test-suite --test262 --unittests --jerry-tests), or with only one .js file.

https://github.com/matedabis/jerryscript/blob/gcov_coverage_tester/tests/gcov-tests/gcovtester.py

While measuring the branch coverage we dont count JERRY_ASSERT s. The results are measured by running all the test scripts, with the modifications in the PRs.

Branch coverage including pando-project#2682 and pando-project#2674:
	-before: 399 / 476
	-after:  472 / 476

There are 28 functions in ecma-builtin-array-prototype.c, we hit 14 from them.
The other 14 functions are either already covered, or we could not improve the coverage of it.

More information about the coverage improvement and the branches not reached:
https://gist.github.com/matedabis/d7b9fc0690aa2f4be6aa160fdf482e0e

While improving the coverage we found an unnecessary condition check, which can not be false in any cases.

Co-authored-by: Csaba Repasi repasics@inf.u-szeged.hu
JerryScript-DCO-1.0-Signed-off-by: Csaba Repasi repasics@inf.u-szeged.hu
JerryScript-DCO-1.0-Signed-off-by: Mate Dabis mdabis@inf.u-szeged.hu

tests/jerry/array-prototype-shift.js

@@ -77,3 +77,61 @@ try {
   assert(e.message === "foo");
   assert(e instanceof ReferenceError);
 }
+
+/* ES v5.1 15.4.4.9.7.c.
+   Checking behavior when the array is freezed */
+try {
+  f = function () { throw new ReferenceError("getter"); };
+  arr =  { length : 9 };
+  Object.defineProperty(arr, '8', { 'get' : f });
+  Array.prototype.shift.call(arr);
+  assert(false);
+} catch (e) {
+  assert(e instanceof ReferenceError);
+  assert(e.message == "getter");
+}
+
+/* ES v5.1 15.4.4.9.7.d.ii.
+   Checking behavior when the array is freezed */
+try {
+  arr =  { length : 9 };
+  Object.defineProperty(arr, '8', { value : 8 });
+  Object.defineProperty(arr, '7', { value : 7 });
+  Array.prototype.shift.call(arr);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+/* ES v5.1 15.4.4.9.7.e.i.
+   Checking behavior when the first element is null */
+try {
+  arr = { length : 9 };
+  Object.defineProperty(arr, '0', { value : null });
+  Array.prototype.shift.call(arr);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+/* ES v5.1 15.4.4.9.8.
+   Checking behavior when last element is not writable */
+try {
+  arr = { length : 9 };
+  Object.defineProperty(arr, '8', { writable : false });
+  Array.prototype.shift.call(arr);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+/* ES v5.1 15.4.4.9.9.
+   Checking behavior when the array is freezed */
+try {
+  arr = { length : 9 };
+  Object.freeze(arr);
+  Array.prototype.shift.call(arr);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}