System.in and System.exit do not work together within the same test

[stevenmanton]

I'm attempting to test a command line runner (based on Spring Batch). Unfortunately, the runner exits rather than, say, returning a value to a trivial wrapper method that exits with that value. In any case, I'd also like to pass data by piping it in through stdin. I can confirm this works in a stand-alone application. However, the mocked data I'm passing into systemInMock doesn't seem to make it to the main method. My code looks something like the following

public class CommandLineRunnerStdInOutTests {

    @Rule
    public final ExpectedSystemExit exit = ExpectedSystemExit.none();

    @Rule
    public final TextFromStandardInputStream systemInMock = emptyStandardInputStream();

    @Rule
    public final StandardOutputStreamLog log = new StandardOutputStreamLog();

    private static final String INPUT_FILE = "data.csv";
    private static final String EXPECTED_FILE = "expected_data.csv";

    @Test
    public void testJob() throws Exception {
        String fileContents = Resources.toString(Resources.getResource(INPUT_FILE), Charsets.UTF_8);
        assertTrue(fileContents.length() >  20);
        systemInMock.provideText(fileContents); // passes: file is read correctly
        exit.expectSystemExitWithStatus(0); // passes: batch job completes, but doesn't see any input records
        CommandLineRunner.main(new String[]{"config.xml", "batchJob"});
    }

    @Test
    public void testFileOut() throws Exception {
        String fileContents = Resources.toString(Resources.getResource(EXPECTED_FILE), Charsets.UTF_8);
        assertEquals(fileContents, log.getLog()); // fails because log.getLog() returns empty String
    }
}

Thanks for writing such an awesome tool! Even with this issue, it has still helped me tremendously!

[stefanbirkner]

The test testFileOut() fails because it doesn't write anything to System.out. JUnit tests (= test methods) are independent. For each of your test methods a new instance of CommandLineRunnerStdInOutTests is created.

Unfortunately I cannot reproduce the problem of testJob(). I created a small application

public class Gh14App {
  public static void main(String... args) throws Exception {
    String output = args [0] + System.in.read() + args[1];
    System.out.write(output.getBytes());
    System.exit(0);
  }
}

and wrote a test

public class Gh14AppTest {

  @Rule
  public final ExpectedSystemExit exit = ExpectedSystemExit.none();

  @Rule
  public final TextFromStandardInputStream systemInMock = emptyStandardInputStream();

  @Rule
  public final StandardOutputStreamLog log = new StandardOutputStreamLog();

  @Test
  public void testJob() throws Exception {
    systemInMock.provideText("A");
    exit.expectSystemExitWithStatus(0);
    Gh14App.main("pre", "post");
    assertThat(log.getLog(), is(equalTo("preApost")));
  }
}

This test runs successfully.

How do you read the input from System.in? Maybe you can provide the code snippet that does this work.

[stevenmanton]

Thanks for the quick response! I'm a little curious about the assertion in testJob(). In my code, it seems that the assertions after the exiting method are never reached. I think that's why you have the method exit.checkAssertionAfterwards(...). So I think that test might be passing simply because the assertion is never called. Can you verify this? if you change your code to

  @Test
  public void testJob() throws Exception {
    systemInMock.provideText("A");
    exit.expectSystemExitWithStatus(0);
    exit.checkAssertionAfterwards(new Assertion() {
      public void checkAssertion() {
        assertThat(log.getLog(), is(equalTo("preApost")));
      }
    });
    Gh14App.main("pre", "post");
  }

does the test still pass? Does it fail if you change to equalTo("XYZ")? If so, then it's probably something buried in how Spring handles stdin. Basically, I just set Spring to read from the file /dev/stdin; it doesn't use Java's System.in method. Still, I would be puzzled because it seems to work just fine when I call my program from the command line. For instance,

cat dat.csv | java -cp myJar.jar  CommandLineRunner

works just fine.

[stefanbirkner]

You're right concerning the assertion stuff. But testJob() is still successful when I use checkAssertionAfterwards (and replace preApost with pre65post) and it fails for equalTo("XYZ").

[stefanbirkner]

If your code reads from the File /dev/stdin then TextFromStandardInputStream won't help you, because it only modifies the InputStream that is returned by System.in.

IMHO you should use the Java abstraction System.in instead of using the file /dev/stdin. In this way your application is more agnostic to its enviroment.

[stevenmanton]

Thanks so much for looking into this. I really appreciate you effort. It seems clear that the problem is in how I handle stdin. Thanks for the advice :-)

[stefanbirkner]

It is my pleasure to help you.