[JS BE] add tests for es6-classes

js/js.translator/testData/box/es6classes/isInitializedFieldBeforeObjectCreation.kt

@@ -0,0 +1,19 @@
+// EXPECTED_REACHABLE_NODES: 1342
+//WITH_RUNTIME
+
+package test
+
+import test.A.p
+
+object A {
+    lateinit var p: String
+    var result: String
+
+    init {
+        result = if (::p.isInitialized) "FAIL" else "OK"
+    }
+}
+
+fun box(): String {
+    return A.result
+}