JS backend: testFiles -> testData

js/js.translator/testData/operatorOverloading/cases/prefixDecOverload.kt

@@ -0,0 +1,18 @@
+package foo
+
+class MyInt() {
+    var b = 0
+
+    fun dec(): MyInt {
+        val res = MyInt()
+        res.b++;
+        return res;
+    }
+}
+
+
+fun box(): Boolean {
+    var c = MyInt()
+    --c;
+    return (c.b == 1);
+}