--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mx/JUnitWrapper.java	Mon Mar 18 19:18:42 2013 +0100
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code 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
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+
+/* Execute testcases by reading names from a given file, due to limits of
+ * the operating system regarding command line size (windows: 32k,
+ * linux [depending on the settings]: ~2097k)
+ * see http://msdn.microsoft.com/en-us/library/ms682425%28VS.85%29.aspx
+ */
+
+import org.junit.runner.*;
+import java.io.*;
+import java.util.*;
+
+public class JUnitWrapper {
+
+    /**
+     * @param args
+     *            args[0] is the path where to read the names of the testclasses.
+     */
+    public static void main(String[] args) {
+        if (args.length == 0) {
+            System.err.printf("wrong usage. provide a filename\n");
+            System.exit(1);
+        }
+        ArrayList<String> tests = new ArrayList<String>(1000);
+        BufferedReader br = null;
+        try {
+            br = new BufferedReader(new FileReader(args[0]));
+
+            String buf;
+            while ((buf = br.readLine()) != null) {
+                tests.add(buf);
+            }
+        } catch (IOException ioe) {
+            ioe.printStackTrace();
+            System.exit(2);
+        } finally {
+            try {
+                if (br != null) {
+                    br.close();
+                }
+            } catch (IOException ioe) {
+                ioe.printStackTrace();
+                System.exit(3);
+            }
+        }
+
+        String[] strargs = tests.toArray(new String[tests.size()]);
+        System.out.printf("executing junit tests now... (%d testclasses)\n", strargs.length);
+        JUnitCore.main(strargs);
+    }
+}

--- a/mx/commands.py	Wed Mar 20 18:38:55 2013 +0100
+++ b/mx/commands.py	Mon Mar 18 19:18:42 2013 +0100
@@ -27,7 +27,7 @@
 # ----------------------------------------------------------------------------------------------------
 
 import os, sys, shutil, zipfile, tempfile, re, time, datetime, platform, subprocess, multiprocessing
-from os.path import join, exists, dirname, basename
+from os.path import join, exists, dirname, basename, getmtime
 from argparse import ArgumentParser, REMAINDER
 import mx
 import sanitycheck
@@ -719,7 +719,7 @@
     matches = lambda line : len([a for a in annotations if line == a or line.startswith(a + '(')]) != 0
     return p.find_classes_with_matching_source_line(pkgRoot, matches, includeInnerClasses)
 
-def _run_tests(args, harness, annotations):
+def _run_tests(args, harness, annotations, testfile):
     pos = [a for a in args if a[0] != '-' and a[0] != '@' ]
     neg = [a[1:] for a in args if a[0] == '-']
     vmArgs = [a[1:] for a in args if a[0] == '@']
@@ -742,13 +742,27 @@
     projectscp = mx.classpath([pcp.name for pcp in mx.projects()])
 
     if len(classes) != 0:
-        harness(projectscp, vmArgs, classes)
+        f_testfile = open(testfile, 'w')
+        for c in classes:
+            f_testfile.write(c + '\n')
+        f_testfile.close()
+        harness(projectscp, vmArgs)
 
 def _unittest(args, annotations):
-    def harness(projectscp, vmArgs, classes):
+    mxdir = dirname(__file__)
+    name = 'JUnitWrapper'
+    javaSource = join(mxdir, name + '.java')
+    javaClass = join(mxdir, name + '.class')
+    (_, testfile) = tempfile.mkstemp(".testclasses", "graal")
+
+    def harness(projectscp, vmArgs):
+        if not exists(javaClass) or getmtime(javaClass) < getmtime(javaSource):
+            subprocess.check_call([mx.java().javac, '-cp', projectscp, '-d', mxdir, javaSource])
         prefixArgs = ['-XX:-BootstrapGraal', '-esa', '-ea']
-        vm(prefixArgs + vmArgs + ['-cp', projectscp, 'org.junit.runner.JUnitCore'] + classes)
-    _run_tests(args, harness, annotations)
+        vm(prefixArgs + vmArgs + ['-cp', projectscp + ':' + mxdir, name] + [testfile])
+
+    _run_tests(args, harness, annotations, testfile)
+    os.remove(testfile)
 
 def unittest(args):
     """run the JUnit tests (all testcases)