JS: move expressions test to box tests

js/js.translator/testData/box/expression/stringTemplates/objectWithToString.kt

@@ -0,0 +1,15 @@
+package foo
+
+class Foo(val name: String) {
+    override public fun toString(): String {
+        return name + "S"
+    }
+}
+
+fun box(): String {
+    val a = Foo("abc")
+    val b = Foo("def")
+    val message = "a = $a, b = $b"
+    assertEquals("a = abcS, b = defS", message)
+    return "OK"
+}