Added unit tests for each of the patterns.

double-checked-locking/pom.xml

@@ -6,4 +6,11 @@
     <version>1.0-SNAPSHOT</version>
   </parent>
   <artifactId>double-checked-locking</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
 </project>

double-checked-locking/src/test/java/com/iluwatar/AppTest.java

@@ -0,0 +1,12 @@
+package com.iluwatar;
+
+import org.junit.Test;
+
+public class AppTest {
+
+	@Test
+	public void test() {
+		String[] args = {};
+		App.main(args);
+	}
+}