@Test
public void isValidFileExtension() throws Exception {

    Assert.assertEquals(true, FileUtil.isValidFileExtension("log"));
    Assert.assertEquals(true, FileUtil.isValidFileExtension("log2"));
    Assert.assertEquals(true, FileUtil.isValidFileExtension("log_bak"));
    Assert.assertEquals(false, FileUtil.isValidFileExtension(".log"));
    Assert.assertEquals(false, FileUtil.isValidFileExtension("$log"));
    Assert.assertEquals(false, FileUtil.isValidFileExtension(" log"));
}