Minor in JS backend tests: use checkFooBoxIsOk instead of fooBoxIsValue

js/js.translator/testData/expression/invoke/cases/invokeMethod.kt

@@ -8,5 +8,6 @@ class Foo(val postfix: String) {
 
 fun box(): String {
     val a = Foo(" world!")
-    return a("hello")
-}
+    assertEquals("hello world!", a("hello"))
+    return "OK"
+}