public SimpleFileSource file(String dir, String fileName) {
		Assert.notNull(dir, "dir should not be null");
		Assert.hasText(fileName, "fileName should not be empty nor null");
		return new SimpleFileSource(dir, fileName);
	}
Construct a new SimpleFileSource using the provided directory and filename

@param dir directory name
@param fileName file name
@return new SimpleFileSource
spring-xd-integration-test/src/main/java/org/springframework/xd/integration/fixtures/Sources.java