@Test
	public void testTailSource() {
		String data = UUID.randomUUID().toString();
		String sourceDir = "/tmp/xd";
		String fileName = UUID.randomUUID().toString() + ".out";

		final String APPEND_TEXT = ".append";
		stream(sources.tail(100, sourceDir + "/" + fileName) + XD_DELIMITER
				+ sinks.file());
		setupSourceDataFiles(sourceDir, fileName, data);
		appendDataToSourceTestFile(sourceDir, fileName, APPEND_TEXT);
		assertValid(data + APPEND_TEXT, sinks.file());
	}
Evaluates whether the tail source (poller) will retrieve the results when the specified file is updated.
spring-xd-integration-test/src/test/java/org/springframework/xd/integration/test/FileSourceTest.java