@Test
public void testListDirectFiles_withFileExtension() throws Exception {

	File dir = this.folder.newFolder();
	Assert.assertTrue( new File( dir, "sub" ).mkdir());
	Assert.assertTrue( new File( dir, "f1.txt" ).createNewFile());
	Assert.assertTrue( new File( dir, "sub/f2.jpg" ).createNewFile());
	Assert.assertTrue( new File( dir, "f3.txt" ).createNewFile());
	Assert.assertTrue( new File( dir, "f4.JPG" ).createNewFile());
	Assert.assertTrue( new File( dir, "sub/f5.zip" ).createNewFile());
	Assert.assertEquals( 1, Utils.listDirectFiles( dir, "jpg" ).size());
	Assert.assertEquals( 1, Utils.listDirectFiles( dir, ".jpg" ).size());
	Assert.assertEquals( 1, Utils.listDirectFiles( dir, "jPg" ).size());
	Assert.assertEquals( 2, Utils.listDirectFiles( dir, "txt" ).size());
	Assert.assertEquals( 0, Utils.listDirectFiles( dir, ".zip" ).size());
	Assert.assertEquals( 3, Utils.listDirectFiles( dir, null ).size());
	Assert.assertEquals( 0, Utils.listDirectFiles( this.folder.newFile(), null ).size());
}