Introduce Checkstyle rule to prohibit class names ending with "Test"

spring-context/src/test/java/example/scannable/PackageMarker.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,10 +16,10 @@
 
 package example.scannable;
 
-
 /**
- * Marker class for example.scannable package.
+ * Marker class for {@code example.scannable} package.
  *
  * @see org.springframework.context.annotation.ComponentScan#basePackageClasses()
  */
-public class _package { }
+public class PackageMarker {
+}