Fix files delete tests

[sumittlearnbay]

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[noojung]

I had the same problem on Windows 11.

After looking into the root cause, I found that the following line was written incorrectly in the first place:

when(mocked.delete()).thenReturn(false);

According to the Mockito javadoc, it is recommended to always use doReturn() for spies:
(Related link: https://javadoc.io/doc/org.mockito/mockito-core/latest/org.mockito/org/mockito/Mockito.html#spy(T))

   List list = new LinkedList();
   List spy = spy(list);

   //Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty)
   when(spy.get(0)).thenReturn("foo");

   //You have to use doReturn() for stubbing
   doReturn("foo").when(spy).get(0);

However, even if you update the code to use doReturn(), the test still fails (and now it fails on macOS as well):

//		when(mocked.delete()).thenReturn(false);
		doReturn(false).when(mocked).delete();

This is because, ItemWriter's close() method actually deletes the file using Files.delete().

Therefore, in my opinion, instead of acquiring a lock with RandomAccessFile, mocking Files.delete() would be a better approach.

Here is my sample code:

	@Test
	void testFailedFileDeletionThrowsException() {
		writer.setShouldDeleteIfEmpty(true);
		writer.open(executionContext);

		try (MockedStatic<Files> mocked = Mockito.mockStatic(Files.class, Mockito.CALLS_REAL_METHODS)) {
			mocked.when(() -> Files.delete(any())).thenThrow(new IOException("Failed to delete file"));

			ItemStreamException exception = assertThrows(ItemStreamException.class, writer::close,
					"Expected exception when file deletion fails");

			assertEquals("Failed to delete empty file on close", exception.getMessage(), "Wrong exception message");
			assertNotNull(exception.getCause(), "Exception should have a cause");
		}
	}

[sumittlearnbay]

Thank you for the explanation and suggestion.

I updated both AbstractFileItemWriterTests and StaxEventItemWriterTests to mock Files.delete() using MockedStatic instead of File.delete(), following your recommendation. I verified the updated tests locally and pushed the changes to this PR.

Please let me know if you see anything else that should be adjusted.

[noojung]

Oh, and it's no big deal, but the filename AbstractFileItemWriterTest.java is missing an 's'.