diff -r 5866e89ef568 -r d382dacfd73f rt/vmtest/src/main/java/org/apidesign/bck2brwsr/vmtest/impl/CompareCase.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rt/vmtest/src/main/java/org/apidesign/bck2brwsr/vmtest/impl/CompareCase.java	Tue Feb 26 16:54:16 2013 +0100
@@ -0,0 +1,160 @@
+/**
+ * Back 2 Browser Bytecode Translator
+ * Copyright (C) 2012 Jaroslav Tulach <jaroslav.tulach@apidesign.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. Look for COPYING file in the top folder.
+ * If not, see http://opensource.org/licenses/GPL-2.0.
+ */
+package org.apidesign.bck2brwsr.vmtest.impl;
+
+import org.apidesign.bck2brwsr.vmtest.*;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.List;
+import org.apidesign.bck2brwsr.launcher.Launcher;
+import org.testng.Assert;
+import org.testng.ITest;
+import org.testng.annotations.Factory;
+import org.testng.annotations.Test;
+
+/** A TestNG {@link Factory} that seeks for {@link Compare} annotations
+ * in provided class and builds set of tests that compare the computations
+ * in real as well as JavaScript virtual machines. Use as:<pre>
+ * {@code @}{@link Factory} public static create() {
+ *   return @{link VMTest}.{@link #create(YourClass.class);
+ * }</pre>
+ *
+ * @author Jaroslav Tulach <jtulach@netbeans.org>
+ */
+public final class CompareCase implements ITest {
+    private final Bck2BrwsrCase first, second;
+    private final Method m;
+    
+    private CompareCase(Method m, Bck2BrwsrCase first, Bck2BrwsrCase second) {
+        this.first = first;
+        this.second = second;
+        this.m = m;
+    }
+
+    /** Inspects <code>clazz</code> and for each {@lik Compare} method creates
+     * instances of tests. Each instance runs the test in different virtual
+     * machine and at the end they compare the results.
+     * 
+     * @param clazz the class to inspect
+     * @return the set of created tests
+     */
+    public static Object[] create(Class<?> clazz) {
+        Method[] arr = clazz.getMethods();
+        List<Object> ret = new ArrayList<>();
+        
+        final LaunchSetup l = LaunchSetup.INSTANCE;
+        ret.add(l);
+        
+        String[] brwsr;
+        {
+            String p = System.getProperty("vmtest.brwsrs");
+            if (p != null) {
+                brwsr = p.split(",");
+            } else {
+                brwsr = new String[0];
+            }
+        }
+        
+        for (Method m : arr) {
+            registerCompareCases(m, l, ret, brwsr);
+            registerBrwsrCases(m, l, ret, brwsr);
+        }
+        return ret.toArray();
+    }
+
+    /** Test that compares the previous results.
+     * @throws Throwable 
+     */
+    @Test(dependsOnGroups = "run") public void compareResults() throws Throwable {
+        Object v1 = first.value;
+        Object v2 = second.value;
+        if (v1 != null) {
+            v1 = v1.toString();
+        } else {
+            v1 = "null";
+        }
+        try {
+            Assert.assertEquals(v2, v1, "Comparing results");
+        } catch (AssertionError e) {
+            StringBuilder sb = new StringBuilder();
+            sb.append(e.getMessage());
+            Bck2BrwsrCase.dumpJS(sb, second);
+            throw new AssertionError(sb.toString());
+        }
+    }
+    
+    /** Test name.
+     * @return name of the tested method followed by a suffix
+     */
+    @Override
+    public String getTestName() {
+        return m.getName() + "[Compare " + second.typeName() + "]";
+    }
+    
+    private static void registerCompareCases(Method m, final LaunchSetup l, List<Object> ret, String[] brwsr) {
+        Compare c = m.getAnnotation(Compare.class);
+        if (c == null) {
+            return;
+        }
+        final Bck2BrwsrCase real = new Bck2BrwsrCase(m, "Java", null, false, null, null);
+        ret.add(real);
+        if (c.scripting()) {
+            final Bck2BrwsrCase js = new Bck2BrwsrCase(m, "JavaScript", l.javaScript(), false, null, null);
+            ret.add(js);
+            ret.add(new CompareCase(m, real, js));
+        }
+        for (String b : brwsr) {
+            final Launcher s = l.brwsr(b);
+            ret.add(s);
+            final Bck2BrwsrCase cse = new Bck2BrwsrCase(m, b, s, false, null, null);
+            ret.add(cse);
+            ret.add(new CompareCase(m, real, cse));
+        }
+    }
+    private static void registerBrwsrCases(Method m, final LaunchSetup l, List<Object> ret, String[] brwsr) {
+        BrwsrTest c = m.getAnnotation(BrwsrTest.class);
+        if (c == null) {
+            return;
+        }
+        HtmlFragment f = m.getAnnotation(HtmlFragment.class);
+        if (f == null) {
+            f = m.getDeclaringClass().getAnnotation(HtmlFragment.class);
+        }
+        Http.Resource[] r = {};
+        Http h = m.getAnnotation(Http.class);
+        if (h == null) {
+            h = m.getDeclaringClass().getAnnotation(Http.class);
+            if (h != null) {
+                r = h.value();
+            }
+        } else {
+            r = h.value();
+        }
+        if (brwsr.length == 0) {
+            final Launcher s = l.brwsr(null);
+            ret.add(s);
+            ret.add(new Bck2BrwsrCase(m, "Brwsr", s, true, f, r));
+        } else {
+            for (String b : brwsr) {
+                final Launcher s = l.brwsr(b);
+                ret.add(s);
+                ret.add(new Bck2BrwsrCase(m, b, s, true, f, r));
+            }
+        }
+    }
+}