added a few classes for doing property change listening (using pure kotlin code so its easier to work with JS and Java)

testlib/test/properties/PropertiesTest.kt

@@ -0,0 +1,51 @@
+package test.properties
+
+import std.*
+import std.properties.*
+import std.util.*
+import stdhack.test.*
+import java.util.*
+import junit.framework.TestCase
+
+class Customer() : ChangeSupport() {
+    // TODO the setter code should be generated
+    // via KT-1299
+    var name: String? = null
+    set(value) {
+        changeProperty("name", $name, value)
+        $name = value
+    }
+
+    var city: String? = null
+    set(value) {
+        changeProperty("city", $city, value)
+        $city = value
+    }
+
+    fun toString() = "Customer($name, $city)"
+}
+
+class MyChangeListener() : ChangeListener {
+    val events = ArrayList<ChangeEvent>()
+
+    override fun onPropertyChange(event: ChangeEvent): Unit {
+        println("Property changed: $event")
+        events.add(event)
+    }
+}
+
+class PropertiesTest() : TestCase() {
+
+    fun testModel() {
+        val c = Customer()
+        c.name = "James"
+        c.city = "Mells"
+
+        val listener = MyChangeListener()
+        c.addChangeListener(listener)
+        c.name = "Andrey"
+        println("Customer $c and raised change events ${listener.events}")
+
+        assertEquals(1, listener.events.size(), "Should have received a change event ${listener.events}")
+    }
+}