Fix for problem with file lock on Windows platform. Introduce unloadPlugins method. (#387)

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pf4j/src/main/java/org/pf4j/AbstractPluginManager.java

         }
     }
 
+    /**
+     * Unload all plugins
+     */
+    @Override
+    public void unloadPlugins() {
+        // wrap resolvedPlugins in new list because of concurrent modification
+        for (PluginWrapper pluginWrapper : new ArrayList<>(resolvedPlugins)) {
+            unloadPlugin(pluginWrapper.getPluginId());
+        }
+    }
+
     /**
      * Unload the specified plugin and it's dependents.
      */

pf4j/src/main/java/org/pf4j/PluginManager.java

      */
     PluginState stopPlugin(String pluginId);
 
+    /**
+     * Unload all plugins
+     */
+    void unloadPlugins();
+
     /**
      * Unload a plugin.
      *

pf4j/src/test/java/org/pf4j/JarPluginManagerTest.java

 
     @AfterEach
     public void tearDown() {
+        pluginManager.unloadPlugins();
+
         pluginJar = null;
         pluginManager = null;
     }