[JS IR BE] Fix and refactor interop tests

js/js.translator/testData/box/trait/checkImplementationCharacteristics.kt

@@ -1,6 +1,4 @@
-// IGNORE_BACKEND: JS_IR
 // EXPECTED_REACHABLE_NODES: 1301
-package foo
 
 public interface A {
     fun foo() {
@@ -11,7 +9,7 @@ public interface B : A {
     }
 }
 
-external class Function(vararg args: String)
+external class Function(args: String, body: String)
 
 val hasProp = Function("obj, prop", "return obj[prop] !== undefined") as ((Any, String) -> Boolean)
 
@@ -27,7 +25,7 @@ fun box(): String {
     if (!hasProp(b, "foo")) return "B hasn't foo"
     if (!hasProp(b, "boo")) return "B hasn't boo"
 
-    val PREFIX = "_.foo"
+    val PREFIX = "_"
     if (eval("$PREFIX.A") == null) return "$PREFIX.A not found"
     if (eval("$PREFIX.B") == null) return "$PREFIX.B not found"
     if (eval("$PREFIX.A === $PREFIX.B") as Boolean) return "A and B refer to the same object"