Java - test a public static void main method with JUnit

Question

I wrote a Java class in which one try to access to a FTP.
I work on Eclipse and I want to make a Junit test on that. I know how to test public classes but I'm stuck at testing a static void main method.

Here is my ftp.java class :

public class ftp {

    public static void main(String[] args) {
        FTPClient client = new FTPClient();

        try {
            client.connect("host");

            // Try to login and return the respective boolean value
            boolean login = client.login("login", "pass");

            // If login is true notify user
            if (login) {
                System.out.println("Connection established...");

                // Try to logout and return the respective boolean value
                boolean logout = client.logout();

                // If logout is true notify user
                if (logout) {
                    System.out.println("Connection close...");
                }
                //  Notify user for failure
            } else {
                System.out.println("Connection fail...");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                // close connection
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

I began to create the ftpTest.java like that :

public class ftpTest {

    ftp testaccess = new ftp();
    FTPClient testclient = ftp.client;


    @Test
    public void testftp() {
        fail("Not yet implemented");
    }

}

Any help would be very appreciated.
Thanks !

Possible duplicate of [Testing main method by junit](https://stackoverflow.com/questions/36349827/testing-main-method-by-junit) — SirFartALot, Mar 29 '19 at 09:58
I already found that post but I wasn't able to use it to solve my problem. What's more the FTP connection looks quite specific. — Julien, Mar 29 '19 at 10:11
Aha, rather than testing the main function you want to test the code as given in the main. That is an other beast. Like triggering those exceptions. — Joop Eggen, Mar 29 '19 at 18:03

score 2 · Answer 1 · answered Mar 29 '19 at 11:02

Since you are not using the command-line arguments, and nor I see any env explicit properties, you refactor the code and move everything to a separate method(s) and test it there.

If you want to do an integration test you might have to spin a full-blown ftp server but that's a bit out of scope for unit tests.

score 1 · Answer 2 · answered Mar 29 '19 at 11:07

@Test
public void testftp() {
    FtpClient.main(new String[0]);
}

That of course is a bit disappointing.

@Test
public void testftp() {
    PrintStream old = System.out;
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    PrintStream out = new PrintStream(baos);
    System.setOut(out);
    FtpClient.main(new String[0]);
    System.out.flush();
    System.setOut(old);
    String s = new String(baos.toByteArray(), Charset.defaultCharset());
    ... check s
}

Capturing the output can give more insight.

Thanks for helping me. I don't understand why you refer to the method main() in public void testftp() ? — Julien, Mar 29 '19 at 14:40

Java - test a public static void main method with JUnit

2 Answers2