[Tests] add coverage

From tc39/test262#4477

Author: ljharb

test/tests.js

@@ -133,4 +133,27 @@ module.exports = function (arrayWith, t) {
 
 		st.end();
 	});
+
+	t.test('test262: test/built-ins/Array/prototype/with/index-throw-completion', function (st) {
+		function MyError() {} // eslint-disable-line func-style
+
+		var index = {
+			valueOf: function () { throw new MyError(); }
+		};
+
+		st['throws'](
+			function () { arrayWith([], index, null); },
+			MyError,
+			'throws on index valueOf'
+		);
+
+		st.end();
+	});
+
+	t.test('test262: test/built-ins/Array/prototype/with/negative-fractional-index-truncated-to-zero', function (st) {
+		var result = arrayWith([0], -0.5, 123);
+		st.equal(result[0], 123);
+
+		st.end();
+	});
 };