diff --git a/libraries/stdlib/test/ArraysTest.kt b/libraries/stdlib/test/ArraysTest.kt
index 77620c63610..4c956fa86db 100644
--- a/libraries/stdlib/test/ArraysTest.kt
+++ b/libraries/stdlib/test/ArraysTest.kt
@@ -1,12 +1,11 @@
 package test.arrays
 
 import kotlin.test.*
+import org.junit.Test as test
 
-import junit.framework.TestCase
+class ArraysTest {
 
-class ArraysTest() : TestCase() {
-
-    fun testCopyOf() {
+    test fun copyOf() {
         checkContent(booleanArray(true, false, true, false, true, false).copyOf().iterator(), 6) { it % 2 == 0 }
         checkContent(byteArray(0, 1, 2, 3, 4, 5).copyOf().iterator(), 6) { it.toByte() }
         checkContent(shortArray(0, 1, 2, 3, 4, 5).copyOf().iterator(), 6) { it.toShort() }
@@ -17,7 +16,7 @@ class ArraysTest() : TestCase() {
         checkContent(charArray('0', '1', '2', '3', '4', '5').copyOf().iterator(), 6) { (it + '0').toChar() }
     }
 
-    fun testCopyOfRange() {
+    test fun copyOfRange() {
         checkContent(booleanArray(true, false, true, false, true, false).copyOfRange(0, 3).iterator(), 3) { it % 2 == 0 }
         checkContent(byteArray(0, 1, 2, 3, 4, 5).copyOfRange(0, 3).iterator(), 3) { it.toByte() }
         checkContent(shortArray(0, 1, 2, 3, 4, 5).copyOfRange(0, 3).iterator(), 3) { it.toShort() }
@@ -39,7 +38,7 @@ class ArraysTest() : TestCase() {
         assertFalse(iter.hasNext, "Invalid length (hasNext)")
     }
 
-    fun testEmptyArrayLastIndex() {
+    test fun emptyArrayLastIndex() {
         val arr1 = IntArray(0)
         assertEquals(-1, arr1.lastIndex)
 
@@ -47,7 +46,7 @@ class ArraysTest() : TestCase() {
         assertEquals(-1, arr2.lastIndex)
     }
 
-    fun testArrayLastIndex() {
+    test fun arrayLastIndex() {
         val arr1 = intArray(0, 1, 2, 3, 4)
         assertEquals(4, arr1.lastIndex)
         assertEquals(4, arr1[arr1.lastIndex])
@@ -57,4 +56,36 @@ class ArraysTest() : TestCase() {
         assertEquals("4", arr2[arr2.lastIndex])
     }
 
+    test fun reduce() {
+        expect(-4) { intArray(1, 2, 3) reduce { a, b -> a - b } }
+        expect(-4.toLong()) { longArray(1, 2, 3) reduce { a, b -> a - b } }
+        expect(-4.toFloat()) { floatArray(1.toFloat(), 2.toFloat(), 3.toFloat()) reduce { a, b -> a - b } }
+        expect(-4.0) { doubleArray(1.0, 2.0, 3.0) reduce { a, b -> a - b } }
+        expect('3') { charArray('1', '3', '2') reduce { a, b -> if(a > b) a else b } }
+        expect(false) { booleanArray(true, true, false) reduce { a, b -> a && b } }
+        expect(true) { booleanArray(true, true) reduce { a, b -> a && b } }
+        expect(0.toByte()) { byteArray(3, 2, 1) reduce { a, b -> (a - b).toByte() } }
+        expect(0.toShort()) { shortArray(3, 2, 1) reduce { a, b -> (a - b).toShort() } }
+
+        failsWith<UnsupportedOperationException> {
+            intArray().reduce { a, b -> a + b}
+        }
+    }
+
+    test fun reduceRight() {
+        expect(2) { intArray(1, 2, 3) reduceRight { a, b -> a - b } }
+        expect(2.toLong()) { longArray(1, 2, 3) reduceRight { a, b -> a - b } }
+        expect(2.toFloat()) { floatArray(1.toFloat(), 2.toFloat(), 3.toFloat()) reduceRight { a, b -> a - b } }
+        expect(2.0) { doubleArray(1.0, 2.0, 3.0) reduceRight { a, b -> a - b } }
+        expect('3') { charArray('1', '3', '2') reduceRight { a, b -> if(a > b) a else b } }
+        expect(false) { booleanArray(true, true, false) reduceRight { a, b -> a && b } }
+        expect(true) { booleanArray(true, true) reduceRight { a, b -> a && b } }
+        expect(2.toByte()) { byteArray(1, 2, 3) reduceRight { a, b -> (a - b).toByte() } }
+        expect(2.toShort()) { shortArray(1, 2, 3) reduceRight { a, b -> (a - b).toShort() } }
+
+        failsWith<UnsupportedOperationException> {
+            intArray().reduceRight { a, b -> a + b}
+        }
+    }
+
 }
diff --git a/libraries/stdlib/test/CollectionTest.kt b/libraries/stdlib/test/CollectionTest.kt
index 5db684f4574..d80743a32d2 100644
--- a/libraries/stdlib/test/CollectionTest.kt
+++ b/libraries/stdlib/test/CollectionTest.kt
@@ -222,11 +222,6 @@ class CollectionTest {
             list.reduce { a, b -> a + b }
         }
 
-        expect(-4) {
-            val array = array(1, 2, 3)
-            array.reduce { a, b -> a - b }
-        }
-
         failsWith<UnsupportedOperationException> {
             arrayList<Int>().reduce { a, b -> a + b}
         }
@@ -237,10 +232,6 @@ class CollectionTest {
             val list = arrayList("1", "2", "3", "4")
             list.reduceRight { a, b -> a + b }
         }
-        expect(2) {
-            val array = array(1, 2, 3)
-            array.reduceRight { a, b -> a - b }
-        }
 
         failsWith<UnsupportedOperationException> {
             arrayList<Int>().reduceRight { a, b -> a + b}