Added copyright header.

src/test/java/com/soebes/module/calculator/FileSystemExtension.java

@@ -1,5 +1,24 @@
 package com.soebes.module.calculator;
 
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
 import com.github.marschall.memoryfilesystem.MemoryFileSystemBuilder;
 import org.junit.jupiter.api.extension.AfterEachCallback;
 import org.junit.jupiter.api.extension.BeforeEachCallback;
@@ -12,6 +31,9 @@
 
 import static java.util.Objects.nonNull;
 
+/**
+ * @author Karl Heinz Marbaise
+ */
 class FileSystemExtension implements BeforeEachCallback, AfterEachCallback, ParameterResolver {
 
   private static final String FILE_SYSTEM = "file_system";