Added fail on missing plugin id

pf4j/src/test/java/ro/fortsoft/pf4j/ManifestPluginDescriptorFinderTest.java

@@ -81,6 +81,17 @@ public class ManifestPluginDescriptorFinderTest {
         PluginDescriptor result = instance.find(new File(url.getPath()));
     }
 
+    /**
+     * Test of find method, of class ManifestPluginDescriptorFinder.
+     */
+    @Test(expected = PluginException.class)
+    public void testFindMissingPluginId() throws Exception {
+
+        ManifestPluginDescriptorFinder instance = new DefaultPluginDescriptorFinder(new PluginClasspath());
+        URL url = getClass().getResource("/test-plugin-6");
+        PluginDescriptor result = instance.find(new File(url.getPath()));
+    }
+
     /**
      * Test of find method, of class ManifestPluginDescriptorFinder.
      */

pf4j/src/test/resources/test-plugin-6/classes/META-INF/MANIFEST.MF

@@ -0,0 +1,13 @@
+Manifest-Version: 1.0
+Implementation-Title: Test Plugin #2
+Implementation-Version: 0.10.0-SNAPSHOT
+Archiver-Version: Plexus Archiver
+Built-By: Mario Franco
+Specification-Title: Test Plugin #2
+Implementation-Vendor-Id: ro.fortsoft.pf4j.demo
+Plugin-Provider: Decebal Suiu
+Plugin-Class: ro.fortsoft.pf4j.plugin.TestPlugin
+Created-By: Apache Maven 3.0.5
+Build-Jdk: 1.8.0_45
+Specification-Version: 0.10.0-SNAPSHOT
+