TempDirWeirdBehavior.java

@TestMethodOrder(OrderAnnotation.class)
public class TestTempDir {

	@Test
	@Order(1)
	public void workInMethod(@TempDir Path tempPathArg) throws IOException {
		File temp = tempPathArg.resolve("temp.txt").toFile();
		FileUtils.write(temp, "temp contents", StandardCharsets.ISO_8859_1);

		assertEquals("temp contents", FileUtils.readFileToString(temp, StandardCharsets.ISO_8859_1));

	}

	@Test
	@Order(2)
	public void workWithInnerClassWorkAround(@TempDir Path tempPathArg) throws IOException {
		FileServiceWorkAround service = new FileServiceWorkAround(tempPathArg.resolve("temp.txt").toFile());
		service.writeToFile("temp contents");
		assertEquals("temp contents", service.readFromFile());
	}

	@Test
	@Order(3)
	public void workWithInnerClass(@TempDir Path tempPathArg) throws IOException {
		FileService service = new FileService(tempPathArg.resolve("temp.txt").toFile());
		service.writeToFile("temp contents");
		assertEquals("temp contents", service.readFromFile());
	}
  
	class FileService {
		private File file;

		public FileService(File file) {
			this.file = file;
		}

		public void writeToFile(String contents) throws IOException {
			if (StringUtils.isEmpty(FileUtils.readFileToString(file, StandardCharsets.ISO_8859_1))) {
				FileUtils.write(file, contents, StandardCharsets.ISO_8859_1);
			} else {
				throw new IOException("File isn't empty!");
			}
		}

		public String readFromFile() throws IOException {
			return FileUtils.readFileToString(file, StandardCharsets.ISO_8859_1);
		}
	}

	class FileServiceWorkAround {
		private File file;

		public FileServiceWorkAround(File file) {
			this.file = file;
			try {
				FileUtils.write(file, "", StandardCharsets.ISO_8859_1);
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}

		public void writeToFile(String contents) throws IOException {
			if (StringUtils.isEmpty(FileUtils.readFileToString(file, StandardCharsets.ISO_8859_1))) {
				FileUtils.write(file, contents, StandardCharsets.ISO_8859_1);
			} else {
				throw new IOException("File isn't empty!");
			}
		}

		public String readFromFile() throws IOException {
			return FileUtils.readFileToString(file, StandardCharsets.ISO_8859_1);
		}
	}

}