diff -r ed48023d1d85 -r 3485327d3080 vmtest/src/main/java/org/apidesign/bck2brwsr/vmtest/impl/CompareCase.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/vmtest/src/main/java/org/apidesign/bck2brwsr/vmtest/impl/CompareCase.java	Sun Dec 23 23:30:06 2012 +0100
@@ -0,0 +1,114 @@
+/**
+ * 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.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.List;
+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 Launchers l = Launchers.INSTANCE;
+    
+        ret.add(l);
+        
+        for (Method m : arr) {
+            Compare c = m.getAnnotation(Compare.class);
+            if (c == null) {
+                continue;
+            }
+            final Bck2BrwsrCase real = new Bck2BrwsrCase(m, 0, null);
+            final Bck2BrwsrCase js = new Bck2BrwsrCase(m, 1, l);
+            final Bck2BrwsrCase brwsr = new Bck2BrwsrCase(m, 2, l);
+            
+            ret.add(real);
+            ret.add(js);
+            ret.add(brwsr);
+            
+            ret.add(new CompareCase(m, real, js));
+            ret.add(new CompareCase(m, real, 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";
+        }
+        Assert.assertEquals(v2, v1, "Comparing results");
+    }
+    
+    /** Test name.
+     * @return name of the tested method followed by a suffix
+     */
+    @Override
+    public String getTestName() {
+        return m.getName() + "[Compare " + second.typeName() + "]";
+    }
+    
+    static StringBuilder dumpJS(CharSequence sb) throws IOException {
+        File f = File.createTempFile("execution", ".js");
+        try (FileWriter w = new FileWriter(f)) {
+            w.append(sb);
+        }
+        return new StringBuilder(f.getPath());
+    }
+}