Introduce 'pairwise' function, KEEP-11

libraries/stdlib/test/text/StringTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -837,6 +837,18 @@ class StringTest {
         assertContentEquals("abc", pair.second, "pair.second")
     }
 
+    @Test fun pairwise() = withOneCharSequenceArg { arg1 ->
+        assertEquals(listOf("ab", "bc"), arg1("abc").pairwise { a, b -> a.toString() + b })
+        assertTrue(arg1("").pairwise { a, b -> a.toString() + b }.isEmpty())
+        assertTrue(arg1("a").pairwise { a, b -> a.toString() + b }.isEmpty())
+    }
+
+    @Test fun pairwisePairs() = withOneCharSequenceArg { arg1 ->
+        assertEquals(listOf('a' to 'b', 'b' to 'c'), arg1("abc").pairwise())
+        assertTrue(arg1("").pairwise().isEmpty())
+        assertTrue(arg1("a").pairwise().isEmpty())
+    }
+
     @Test fun map() = withOneCharSequenceArg { arg1 ->
         assertEquals(listOf('a', 'b', 'c'), arg1("abc").map { it })