fixed unit test

main/filesystem-api/src/main/java/org/cryptomator/filesystem/delegating/DelegatingFolder.java

@@ -83,7 +83,7 @@ public abstract class DelegatingFolder<D extends DelegatingFolder<D, F>, F exten
 			final Folder delegateDest = ((DelegatingFolder<?, ?>) destination).delegate;
 			delegate.copyTo(delegateDest);
 		} else {
-			Folder.super.copyTo(destination);
+			throw new IllegalArgumentException("Can only copy DelegatingFolder to other DelegatingFolder.");
 		}
 	}
 

main/filesystem-api/src/test/java/org/cryptomator/filesystem/delegating/DelegatingFolderTest.java

@@ -133,14 +133,13 @@ public class DelegatingFolderTest {
 		Mockito.verify(mockFolder1).copyTo(mockFolder2);
 	}
 
-	@Test
+	@Test(expected = IllegalArgumentException.class)
 	public void testCopyToDestinationFromDifferentLayer() {
 		Folder mockFolder1 = Mockito.mock(Folder.class);
 		Folder mockFolder2 = Mockito.mock(Folder.class);
 		DelegatingFolder<?, ?> delegatingFolder1 = new TestDelegatingFolder(null, mockFolder1);
 
 		delegatingFolder1.copyTo(mockFolder2);
-		Mockito.verify(mockFolder1).copyTo(mockFolder2);
 	}
 
 	@Test