diff -r 2291e553464a -r b9318fe303cd vm/src/test/java/org/apidesign/vm4brwsr/InstanceTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/vm/src/test/java/org/apidesign/vm4brwsr/InstanceTest.java	Mon Sep 24 11:07:38 2012 +0200
@@ -0,0 +1,101 @@
+/*
+ * To change this template, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package org.apidesign.vm4brwsr;
+
+import javax.script.Invocable;
+import javax.script.ScriptException;
+import org.testng.annotations.Test;
+import static org.testng.Assert.*;
+
+/**
+ *
+ * @author Jaroslav Tulach <jtulach@netbeans.org>
+ */
+public class InstanceTest {
+    @Test public void verifyDefaultDoubleValue() throws Exception {
+        assertExec(
+            "Will be zero",
+            "org_apidesign_vm4brwsr_Instance_defaultDblValueD",
+            Double.valueOf(0)
+        );
+    }
+    @Test public void verifyAssignedByteValue() throws Exception {
+        assertExec(
+            "Will one thirty one",
+            "org_apidesign_vm4brwsr_Instance_assignedByteValueB",
+            Double.valueOf(31)
+        );
+    }
+    @Test public void verifyMagicOne() throws Exception {
+        assertExec(
+            "Should be three and something",
+            "org_apidesign_vm4brwsr_Instance_magicOneD",
+            Double.valueOf(3.3)
+        );
+    }
+    @Test public void verifyInstanceMethods() throws Exception {
+        assertExec(
+            "Should be eleven as we invoke overwritten method, plus 44",
+            "org_apidesign_vm4brwsr_Instance_virtualBytesI",
+            Double.valueOf(55)
+        );
+    }
+    @Test public void verifyInterfaceMethods() throws Exception {
+        assertExec(
+            "Retruns default value",
+            "org_apidesign_vm4brwsr_Instance_interfaceBytesF",
+            Double.valueOf(31)
+        );
+    }
+
+    @Test public void isNull() throws Exception {
+        assertExec(
+            "Yes, we are instance",
+            "org_apidesign_vm4brwsr_Instance_isNullZ",
+            Double.valueOf(0.0)
+        );
+    }
+
+    @Test public void isInstanceOf() throws Exception {
+        assertExec(
+            "Yes, we are instance",
+            "org_apidesign_vm4brwsr_Instance_instanceOfZZ",
+            Double.valueOf(1.0), true
+        );
+    }
+
+    @Test public void notInstanceOf() throws Exception {
+        assertExec(
+            "No, we are not an instance",
+            "org_apidesign_vm4brwsr_Instance_instanceOfZZ",
+            Double.valueOf(0.0), false
+        );
+    }
+    
+    private static void assertExec(String msg, String methodName, Object expRes, Object... args) throws Exception {
+        StringBuilder sb = new StringBuilder();
+        Invocable i = StaticMethodTest.compileClass(sb, 
+            "org/apidesign/vm4brwsr/Instance"
+        );
+        
+        Object ret = null;
+        try {
+            ret = i.invokeFunction(methodName, args);
+        } catch (ScriptException ex) {
+            fail("Execution failed in " + sb, ex);
+        } catch (NoSuchMethodException ex) {
+            fail("Cannot find method in " + sb, ex);
+        }
+        if (ret == null && expRes == null) {
+            return;
+        }
+        if (expRes.equals(ret)) {
+            return;
+        }
+        assertEquals(ret, expRes, msg + "was: " + ret + "\n" + sb);
+        
+    }
+    
+}