Add utility class tests (#871)

Checks for classes that only have static methods.

wpilibj/src/main/java/edu/wpi/first/wpilibj/livewindow/LiveWindow.java

@@ -45,6 +45,10 @@ public class LiveWindow {
   private static boolean liveWindowEnabled = false;
   private static boolean telemetryEnabled = true;
 
+  private LiveWindow() {
+    throw new UnsupportedOperationException("This is a utility class!");
+  }
+
   public static synchronized boolean isEnabled() {
     return liveWindowEnabled;
   }