Initial implementation of method separators

#KT-13029 Fixed

compiler/tests-common/tests/org/jetbrains/kotlin/test/InTextDirectivesUtils.java

@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed 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.
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.test;
@@ -115,6 +104,9 @@ public final class InTextDirectivesUtils {
 
     @NotNull
     public static List<String> findLinesWithPrefixesRemoved(String fileText, boolean trim, String... prefixes) {
+        if (prefixes.length == 0) {
+            throw new IllegalArgumentException("Please specify the prefixes to check");
+        }
         List<String> result = new ArrayList<>();
         List<String> cleanedPrefixes = cleanDirectivesFromComments(Arrays.asList(prefixes));