Check for index-out-of-bound in elementAt function (KT-30051)

libraries/stdlib/test/collections/ArraysTest.kt

@@ -1490,6 +1490,16 @@ class ArraysTest {
         array.sortWith(comparator)
         array.iterator().assertSorted { a, b -> comparator.compare(a, b) <= 0 }
     }
+
+    @Test
+    fun elementAt() {
+        expect(0) { byteArrayOf(0, 1, 2).elementAt(0) }
+        expect(1) { shortArrayOf(0, 1, 2).elementAt(1) }
+        expect(2) { intArrayOf(0, 1, 2).elementAt(2) }
+
+        assertFailsWith<IndexOutOfBoundsException> { arrayOf<String>().elementAt(0) }
+        assertFailsWith<IndexOutOfBoundsException> { longArrayOf(0, 1, 2).elementAt(-1) }
+    }
 }
 
 

libraries/stdlib/test/collections/UnsignedArraysTest.kt

@@ -625,10 +625,8 @@ class UnsignedArraysTest {
         expect(1u) { ushortArrayOf(0, 1, 2).elementAt(1) }
         expect(2u) { uintArrayOf(0, 1, 2).elementAt(2) }
 
-        // TODO: Uncomment these tests after KT-30051 gets fixed.
-        // Currently JS does not throw exception on incorrect index.
-//        assertFailsWith<IndexOutOfBoundsException> { uintArrayOf().elementAt(0) }
-//        assertFailsWith<IndexOutOfBoundsException> { ulongArrayOf(0, 1, 2).elementAt(-1) }
+        assertFailsWith<IndexOutOfBoundsException> { uintArrayOf().elementAt(0) }
+        assertFailsWith<IndexOutOfBoundsException> { ulongArrayOf(0, 1, 2).elementAt(-1) }
     }
 
     @Test

libraries/stdlib/test/text/StringTest.kt

@@ -1460,4 +1460,14 @@ ${"    "}
         assertEquals("  ABC\n   \n  123", "ABC\n   \n123".prependIndent("  "))
         assertEquals("  ", "".prependIndent("  "))
     }
+
+    @Test
+    fun elementAt() {
+        expect('a') { "a c".elementAt(0) }
+        expect(' ') { "a c".elementAt(1) }
+        expect('c') { "a c".elementAt(2) }
+
+        assertFailsWith<IndexOutOfBoundsException> { "".elementAt(0) }
+        assertFailsWith<IndexOutOfBoundsException> { "a c".elementAt(-1) }
+    }
 }