StringBuilder builder and appendln

libraries/stdlib/test/text/StringBuilderTest.kt

@@ -0,0 +1,28 @@
+package test.text
+
+import kotlin.test.*
+import org.junit.Test as test
+
+class StringBuilderTest {
+
+    test fun stringBuild() {
+        val s = StringBuilder {
+            append("a")
+            append(true)
+        }.toString()
+        assertEquals("atrue", s)
+    }
+
+    test fun appendMany() {
+        assertEquals("a1", StringBuilder().append("a", "1").toString())
+        assertEquals("a1", StringBuilder().append("a", 1).toString())
+        assertEquals("a1", StringBuilder().append("a", StringBuilder().append("1")).toString())
+    }
+
+    test fun append() {
+        // this test is needed for JS implementation
+        assertEquals("em", StringBuilder {
+            append("element", 2, 4)
+        }.toString())
+    }
+}