diff --git a/core/src/test/java/org/elasticsearch/bootstrap/JarHellTests.java b/core/src/test/java/org/elasticsearch/bootstrap/JarHellTests.java
new file mode 100644
index 00000000000..d87a7e295f1
--- /dev/null
+++ b/core/src/test/java/org/elasticsearch/bootstrap/JarHellTests.java
@@ -0,0 +1,206 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.bootstrap;
+
+import org.elasticsearch.test.ElasticsearchTestCase;
+
+import java.io.ByteArrayOutputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.net.URL;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.jar.Attributes;
+import java.util.jar.JarOutputStream;
+import java.util.jar.Manifest;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipOutputStream;
+
+public class JarHellTests extends ElasticsearchTestCase {
+
+    URL makeJar(Path dir, String name, Manifest manifest, String... files) throws IOException {
+        Path jarpath = dir.resolve(name);
+        ZipOutputStream out;
+        if (manifest == null) {
+            out = new JarOutputStream(Files.newOutputStream(jarpath, StandardOpenOption.CREATE));
+        } else {
+            out = new JarOutputStream(Files.newOutputStream(jarpath, StandardOpenOption.CREATE), manifest);
+        }
+        for (String file : files) {
+            out.putNextEntry(new ZipEntry(file));
+        }
+        out.close();
+        return jarpath.toUri().toURL();
+    }
+
+    URL makeFile(Path dir, String name) throws IOException {
+        Path filepath = dir.resolve(name);
+        Files.newOutputStream(filepath, StandardOpenOption.CREATE).close();
+        return filepath.toUri().toURL();
+    }
+
+    public void testDifferentJars() throws Exception {
+        Path dir = createTempDir();
+        URL[] jars = {makeJar(dir, "foo.jar", null, "DuplicateClass.class"), makeJar(dir, "bar.jar", null, "DuplicateClass.class")};
+        try {
+            JarHell.checkJarHell(jars);
+        } catch (IllegalStateException e) {
+            assertTrue(e.getMessage().contains("jar hell!"));
+            assertTrue(e.getMessage().contains("DuplicateClass"));
+            assertTrue(e.getMessage().contains("foo.jar"));
+            assertTrue(e.getMessage().contains("bar.jar"));
+        }
+    }
+
+    public void testBootclasspathLeniency() throws Exception {
+        Path dir = createTempDir();
+        String previousJavaHome = System.getProperty("java.home");
+        System.setProperty("java.home", dir.toString());
+        URL[] jars = {makeJar(dir, "foo.jar", null, "DuplicateClass.class"), makeJar(dir, "bar.jar", null, "DuplicateClass.class")};
+        try {
+            JarHell.checkJarHell(jars);
+        } finally {
+            System.setProperty("java.home", previousJavaHome);
+        }
+    }
+
+    public void testDuplicateClasspathLeniency() throws Exception {
+        Path dir = createTempDir();
+        URL jar = makeJar(dir, "foo.jar", null, "Foo.class");
+        URL[] jars = {jar, jar};
+        JarHell.checkJarHell(jars);
+    }
+
+    public void testDirsOnClasspath() throws Exception {
+        Path dir1 = createTempDir();
+        Path dir2 = createTempDir();
+        URL[] dirs = {makeFile(dir1, "DuplicateClass.class"), makeFile(dir2, "DuplicateClass.class")};
+        try {
+            JarHell.checkJarHell(dirs);
+        } catch (IllegalStateException e) {
+            assertTrue(e.getMessage().contains("jar hell!"));
+            assertTrue(e.getMessage().contains("DuplicateClass"));
+            assertTrue(e.getMessage().contains(dir1.toString()));
+            assertTrue(e.getMessage().contains(dir2.toString()));
+        }
+    }
+
+    public void testDirAndJar() throws Exception {
+        Path dir1 = createTempDir();
+        Path dir2 = createTempDir();
+        URL[] dirs = {makeJar(dir1, "foo.jar", null, "DuplicateClass.class"), makeFile(dir2, "DuplicateClass.class")};
+        try {
+            JarHell.checkJarHell(dirs);
+        } catch (IllegalStateException e) {
+            assertTrue(e.getMessage().contains("jar hell!"));
+            assertTrue(e.getMessage().contains("DuplicateClass"));
+            assertTrue(e.getMessage().contains("foo.jar"));
+            assertTrue(e.getMessage().contains(dir2.toString()));
+        }
+    }
+
+    public void testLog4jLeniency() throws Exception {
+        Path dir = createTempDir();
+        URL[] jars = {makeJar(dir, "foo.jar", null, "org/apache/log4j/DuplicateClass.class"), makeJar(dir, "bar.jar", null, "org/apache/log4j/DuplicateClass.class")};
+        JarHell.checkJarHell(jars);
+    }
+
+    public void testBaseDateTimeLeniency() throws Exception {
+        Path dir = createTempDir();
+        URL[] jars = {makeJar(dir, "foo.jar", null, "org/joda/time/base/BaseDateTime.class"), makeJar(dir, "bar.jar", null, "org/joda/time/base/BaseDateTime.class")};
+        JarHell.checkJarHell(jars);
+    }
+
+    public void testWithinSingleJar() throws Exception {
+        // the java api for zip file does not allow creating duplicate entries (good!) so
+        // this bogus jar had to be constructed with ant
+        URL[] jars = {JarHellTests.class.getResource("duplicate-classes.jar")};
+        try {
+            JarHell.checkJarHell(jars);
+        } catch (IllegalStateException e) {
+            assertTrue(e.getMessage().contains("jar hell!"));
+            assertTrue(e.getMessage().contains("DuplicateClass"));
+            assertTrue(e.getMessage().contains("duplicate-classes.jar"));
+            assertTrue(e.getMessage().contains("exists multiple times in jar"));
+        }
+    }
+
+    public void testXmlBeansLeniency() throws Exception {
+        URL[] jars = {JarHellTests.class.getResource("duplicate-xmlbeans-classes.jar")};
+        JarHell.checkJarHell(jars);
+    }
+
+    public void testRequiredJDKVersionTooOld() throws Exception {
+        Path dir = createTempDir();
+        String previousJavaVersion = System.getProperty("java.specification.version");
+        System.setProperty("java.specification.version", "1.7");
+
+        Manifest manifest = new Manifest();
+        manifest.getMainAttributes().put(new Attributes.Name("X-Compile-Target-JDK"), "1.8");
+        URL[] jars = {makeJar(dir, "foo.jar", manifest, "Foo.class")};
+        try {
+            JarHell.checkJarHell(jars);
+        } catch (IllegalStateException e) {
+            assertTrue(e.getMessage().contains("requires java 1.8"));
+            assertTrue(e.getMessage().contains("your system: 1.7"));
+        } finally {
+            System.setProperty("java.specification.version", previousJavaVersion);
+        }
+    }
+
+    public void testRequiredJDKVersionIsOK() throws Exception {
+        Path dir = createTempDir();
+        String previousJavaVersion = System.getProperty("java.specification.version");
+        System.setProperty("java.specification.version", "1.7");
+
+        Manifest manifest = new Manifest();
+        manifest.getMainAttributes().put(new Attributes.Name("X-Compile-Target-JDK"), "1.7");
+        URL[] jars = {makeJar(dir, "foo.jar", manifest, "Foo.class")};
+        try {
+            JarHell.checkJarHell(jars);
+        } finally {
+            System.setProperty("java.specification.version", previousJavaVersion);
+        }
+    }
+
+    public void testBadJDKVersionProperty() throws Exception {
+        Path dir = createTempDir();
+        String previousJavaVersion = System.getProperty("java.specification.version");
+        System.setProperty("java.specification.version", "bogus");
+
+        Manifest manifest = new Manifest();
+        manifest.getMainAttributes().put(new Attributes.Name("X-Compile-Target-JDK"), "1.7");
+        URL[] jars = {makeJar(dir, "foo.jar", manifest, "Foo.class")};
+        try {
+            JarHell.checkJarHell(jars);
+        } finally {
+            System.setProperty("java.specification.version", previousJavaVersion);
+        }
+    }
+
+    public void testBadJDKVersionInJar() throws Exception {
+        Path dir = createTempDir();
+        Manifest manifest = new Manifest();
+        manifest.getMainAttributes().put(new Attributes.Name("X-Compile-Target-JDK"), "bogus");
+        URL[] jars = {makeJar(dir, "foo.jar", manifest, "Foo.class")};
+        JarHell.checkJarHell(jars);
+    }
+}
diff --git a/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-classes.jar b/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-classes.jar
new file mode 100644
index 00000000000..a7d9c55bff3
Binary files /dev/null and b/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-classes.jar differ
diff --git a/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-xmlbeans-classes.jar b/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-xmlbeans-classes.jar
new file mode 100644
index 00000000000..a5d3abca13e
Binary files /dev/null and b/core/src/test/resources/org/elasticsearch/bootstrap/duplicate-xmlbeans-classes.jar differ