重定向 System.in ByteArrayInputStream 被读取一个 JUnit 测试为时已晚

Question

I am Currently writing Junit tests for automated testing of student tasks. The topic is console input in java. I have multiple tests that need to take simulated user input and check for correct behaviour of tested methods (method is working fine).

My problem at the moment: the ByteArrayInputStream set as System.in won't release when needed but one test later (see pic below).

I tried to reset the stream, make it static, make it non-static, have standard System.in set before and after, tried read method, switched java-versions (from SE13 to 1.8). All attempts at different times, ofc.

Explanation of output in the picture:

It's from our automated JUnit-Framework. Those are two tests reliant on the tested method that takes a user input. The "?" at the start of a line indicate the tested method is active and waiting. First two words after the STARTING TEST line are what is supposed to get injected.

JUnit test code:

final  static InputStream STDIN = System.in;
static ByteArrayInputStream bais;
final static String[] INJECTIONS = { "abc", "def", "ghi", "jkl", "mmmm", "klopp", "urgl", "gurle", "ding", "dong" };

private static void inject(String injection, Object o, MethodSignature ms) {
    System.out.println(injection);

    try {
        ByteArrayInputStream bais = new ByteArrayInputStream(injection.getBytes("UTF-8"));

        System.setIn(bais);
        System.out.println("Injection Bytes: "+injection.getBytes().length);
        System.out.println("Available for injection: " + System.in.available());

        ms.getMethod().invoke(o);

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        System.setIn(STDIN);
    }
}

private static String getStringInject(String injection, Object o, MethodSignature ms) {
    String out = null;
    System.out.println(injection);
    try {

        ByteArrayInputStream bais = new ByteArrayInputStream(injection.getBytes("UTF-8"));

        System.setIn(bais);
        System.out.println("Injection Bytes: "+injection.getBytes().length);
        System.out.println("Available for injection: " + System.in.available());
        System.in.reset();
        out = (String) ms.getMethod().invoke(o);

    } catch (Exception e) {
        e.printStackTrace();
    }
    finally {
        System.setIn(STDIN);
    }
    return out;
}

@Test
public void checkReadFromConsoleCorrectReturnTest() {

    Object o = createObject(csMain.getC());
    if (o == null) {
        addFail(csMain.getObjectFail());
        return;
    }
    String injection = INJECTIONS[ThreadLocalRandom.current().nextInt(0, INJECTIONS.length)];

    String output = getStringInject(injection + System.lineSeparator() + "END" + System.lineSeparator(), o,
            msReadFromConsole);

    if (output == null || output.isEmpty()) {
        addFail(msReadFromConsole.getMethodNoReturnString());
        return;
    }

}

@Test
public void checkReadCorrectEndingTriggerTest() {

    Object o = createObject(csMain.getC());
    if (o == null) {
        addFail(csMain.getObjectFail());
        return;
    }
    String injection = INJECTIONS[ThreadLocalRandom.current().nextInt(0, INJECTIONS.length)]
            + System.lineSeparator() + "END" + System.lineSeparator();


    inject(injection, o, msRead);
}

Tested java methods:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;

public class ConsoleReader implements IConsoleReader {

    ArrayList<String> reads;
    BufferedReader br;

    public ConsoleReader() {
        reads = new ArrayList<String>();
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    public void read() {
        String input = readFromConsole();
        while (true) {
            if (input == null || input.isEmpty()) {
                System.out.println("ERROR: null");
                return;
            }
            input = input.trim().toUpperCase();

            if (input.equals("END")) {
                System.out.println("Done.");
                return;
            }

            reads.add(input);
            input = readFromConsole();
        }
    }

    public String readFromConsole() {
        System.out.print("? ");
        String out = null;
        try {
            out = br.readLine();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        System.out.println(out);
        return out;
    }
}

Help is much appreciated. Can't change the Junit library used or add other external libraries atm.

Answer 1

I wrote the following snippet for you to run:

@Test
public void test_byteArrayInputStream() {
    InputStream STDIN = System.in;
    String message = "test" + System.lineSeparator();
    try (ByteArrayInputStream in = new ByteArrayInputStream(message.getBytes("UTF-8"))) {
        System.setIn(in);

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        assertEquals("test", br.readLine()); // this succeeds
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        System.setIn(STDIN);
    }
}

As you can see, the BufferedReader correctly ready "test" from the in stream. I used the AutoClosable aspect of ByteArrayInputStream to close it after the code block.

Since this does not solve your problem, I am uncertain whether the problem does not originate in the surrounding framework. More specifically, the only explanation I can think of for the leap over of values from Testcase 1 to Testcase 2 is, that the object is not reinstantiated, but reused somehow. Since this code is missing, it cannot be said for sure.