[java/cs] Add test

Closes #2688

tests/unit/src/unit/issues/Issue2688.hx

@@ -0,0 +1,36 @@
+package unit.issues;
+
+class Issue2688 extends Test {
+#if (java || cs)
+  public function test() {
+    var x = 0;
+    var b = new B(function() {
+      x++;
+    });
+    b.tasks(10);
+    eq(x, 10);
+  }
+#end
+}
+
+#if (java || cs)
+@:nativeGen
+private class A {
+  public function new() {
+  }
+}
+
+@:nativeGen
+private class B extends A {
+  public var tasks:Int->Void;
+
+  public function new(task:Void->Void) {
+    super();
+    tasks = function(i) {
+      for (j in 0...i) {
+        task();
+      }
+    }
+  }
+}
+#end