public static String file2String(final String fileName) throws IOException {
        File file = new File(fileName);
        return file2String(file);
    }
@Test
    public void testFile2String() throws IOException {
        String fileName = System.getProperty("java.io.tmpdir") + File.separator + "MixAllTest" + System.currentTimeMillis();
        File file = new File(fileName);
        if (file.exists()) {
            file.delete();
        }
        file.createNewFile();
        PrintWriter out = new PrintWriter(fileName);
        out.write("TestForMixAll");
        out.close();
        String string = MixAll.file2String(fileName);
        assertThat(string).isEqualTo("TestForMixAll");
        file.delete();
    }