public String loadData() {
    var dataFileName = this.fileName;
    try (var br = new BufferedReader(new FileReader(dataFileName))) {
      var result = br.lines().collect(Collectors.joining("\n"));
      this.loaded = true;
      return result;
    } catch (Exception e) {
      LOGGER.error("File {} does not exist", dataFileName);
    }

    return null;
  }
@Test
  void testLoadData() {
    final var fileLoader = new FileLoader();
    fileLoader.setFileName("non-existing-file");
    assertNull(fileLoader.loadData());
  }