Add testGetIllegalFileNameChars

Author: garydgregory

src/test/java/org/apache/commons/io/FileSystemTest.java

@@ -19,6 +19,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.apache.commons.lang3.SystemUtils;
@@ -49,6 +50,12 @@ void testGetCurrent() {
         }
     }
 
+    @Test
+    void testGetIllegalFileNameChars() {
+        final FileSystem current = FileSystem.getCurrent();
+        assertNotSame(current.getIllegalFileNameChars(), current.getIllegalFileNameChars());
+    }
+
     @Test
     void testIsLegalName() {
         for (final FileSystem fs : FileSystem.values()) {