JS: move expressions test to box tests

js/js.translator/testData/box/expression/cast/castToNotNull.kt

@@ -0,0 +1,18 @@
+package foo
+
+interface A
+
+class AImpl: A
+
+fun test(x: Any?): A = x as A
+
+fun box(): String {
+    var a: A = AImpl()
+    assertEquals(a, test(a), "a = AImpl()")
+    a = object : A {}
+    assertEquals(a, test(a), "a = object : A{}")
+    failsClassCast("test(null)") { test(null) }
+    failsClassCast("test(object{})") { test(object{}) }
+
+    return "OK"
+}