Add more javadoc for exposed test classes

pf4j/src/test/java/org/pf4j/test/AnotherFailTestPlugin.java

@@ -18,6 +18,9 @@ package org.pf4j.test;
 import org.pf4j.Plugin;
 
 /**
+ * A wrong {@link org.pf4j.Plugin}.
+ * It's wrong because it doesn't contain a constructor with one parameter ({@link org.pf4j.PluginWrapper} as parameter type).
+ *
  * @author Mario Franco
  */
 public class AnotherFailTestPlugin extends Plugin {

pf4j/src/test/java/org/pf4j/test/FailTestExtension.java

@@ -18,6 +18,9 @@ package org.pf4j.test;
 import org.pf4j.Extension;
 
 /**
+ * A wrong {@link org.pf4j.Extension}.
+ * It's wrong because it doesn't contain a constructor with empty parameters (or only the default constructor).
+ *
  * @author Mario Franco
  */
 @Extension

pf4j/src/test/java/org/pf4j/test/FailTestPlugin.java

@@ -16,6 +16,9 @@
 package org.pf4j.test;
 
 /**
+ * A wrong {@link org.pf4j.Plugin}.
+ * It's wrong because it doesn't extends {@link org.pf4j.Plugin}.
+ *
  * @author Mario Franco
  */
 public class FailTestPlugin {

pf4j/src/test/java/org/pf4j/test/TestExtension.java

@@ -18,6 +18,8 @@ package org.pf4j.test;
 import org.pf4j.Extension;
 
 /**
+ * A simple {@link Extension}. It implements {@link TestExtensionPoint}.
+ *
  * @author Mario Franco
  */
 @Extension

pf4j/src/test/java/org/pf4j/test/TestExtensionPoint.java

@@ -18,6 +18,8 @@ package org.pf4j.test;
 import org.pf4j.ExtensionPoint;
 
 /**
+ * A simple {@link ExtensionPoint} that contains one method ({@link #saySomething()}).
+ *
  * @author Mario Franco
  */
 public interface TestExtensionPoint extends ExtensionPoint {

pf4j/src/test/java/org/pf4j/test/TestPlugin.java

@@ -19,6 +19,11 @@ import org.pf4j.Plugin;
 import org.pf4j.PluginWrapper;
 
 /**
+ * A simple {@link Plugin}.
+ *
+ * In real applications you don't need to create a plugin like this if you are not interested in lifecycle events.
+ * {@codes PF4J} will automatically create a plugin similar to this (empty / dummy) if no class plugin is specified.
+ *
  * @author Mario Franco
  */
 public class TestPlugin extends Plugin {

pf4j/src/test/java/org/pf4j/test/package-info.java

@@ -0,0 +1,6 @@
+/**
+ * Classes used to test different aspects of PF4J (plugins, extensions points, extensions).
+ *
+ * @author Decebal Suiu
+ */
+package org.pf4j.test;