JMockit: howto invoke custom method of MockUp

Question

My application use FastScanner (based on BufferedReader) to read input (Look at code section of my question).

If I want to substitute input in my tests I should mock up FastScanner (Look at code section of my question).

Problem: For each input I should make separate mockup. It'll be greate if I can switch input inside the single Mock Up.

Question: How to add custom methods to JMockit MockUps and than call them? (Look at switchInput method of FastScanner mockup)

Code: [This section is optional, only for your better understanding]

FastScanner

protected static class FastScanner {
    BufferedReader br;
    StringTokenizer st;

    FastScanner(InputStream f) {
        br = new BufferedReader(new InputStreamReader(f));
    }

    String next() throws IOException {
        while (st == null || !st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }

    int nextInt() throws IOException {
        return Integer.parseInt(next());
    }
}

FastScanner MockUp:

new MockUp<FastScanner>() {

        private int[] input1 = new int[] {17, 2, 3, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1};
        private int[] input2 = new int[] {5, 2, 2, 3, 3, 3, 3, 3};
        private int[] input3 = new int[] {8, 2, 5, 1, 3, 1, 1, 1, 1, 3, 1};
        private byte toggler = 1;
        private byte pointer = 0;

        //HERE THE QUESTION: HOW CAN I CALL THIS METHOD
        public void switchInput() { 
            toggler++;
            pointer = 0;
        }

        @SuppressWarnings("unused")
        int nextInt() throws IOException {
            int[] input = null;
            switch (toggler) {
                case 1: input = input1; break;
                case 2: input = input2; break;
                case 3: input = input3; break;
            }
            return input[pointer++];
        }
    };

@Andy how can I try? I can't make `switchInput` static and it doesn't belong to `FastScanner` API. So Java just don't see that method at compiling time — VB_, May 06 '14 at 10:48
Oh, you want to call ``switchInput()`` from outside the mock. Hm, why do even want to do that? why not create 3 different mocks? — Andy, May 06 '14 at 10:52
@Andy suppose I want to test about hundred inputs. Than I should create 100 mockups. One hundred mockups is a bad idea — VB_, May 06 '14 at 10:53
@Andy maybe there is some hack, and it's possible in other way? — VB_, May 06 '14 at 10:55
Another way could be to create a subclass of ``FastScanner`` where you implement the methods that you need, if it is possible to set the instance where it is used. — Andy, May 06 '14 at 11:01

score 1 · Accepted Answer · answered May 06 '14 at 15:20

You can't have multiple instances of the same MockUp subclass at the same time (each such mock-up would simply override the previous one when it got instantiated). Instead, add an Invocation parameter to your @Mock method, and then use the information it provides to distinguish between multiple data sets. For example:

@Test
public void testClientWithVariedDataFromFastScanners()
{
    new MockUp<FastScanner>() {
        // some data structure for test data

        @Mock
        int nextInt(Invocation inv) {
            int idx = inv.getInvocationIndex();
            FastScanner fs = inv.getInvokedInstance();

            // Find the next value by using idx or fs as a lookup index
            // into the data structures:
            int i = ...

            return i;
        }
    };

    client.doSomethingUsingFastScanners();
}

Also, if you want to call whatever methods (including static methods) on a mock-up subclass, just make it a named class rather than an anonymous one.

1) The problem of `Invocation` is that in compiling time I don't know when to switch input (after which amount of `nextInt` invocation). 2) I've write `MockUp scannerMockUp = new MockUp()` but I still can't invoke custom methods! Where is mistake? — VB_, May 07 '14 at 07:49
The mistake is that you are still using an *anonymous* mock-up class. Instead, create a *named* mock-up class (ie, a regular class which extends `MockUp` and has a name). — Rogério, May 07 '14 at 15:36

VB_ · Answer 2 · 2014-05-07T09:38:33.040

Maybe it is worse solution than @Rogerio's one, but we can use outer classes with static fields. I mean:

    new MockUp<PrisonTransfer.FastScanner>() {

        private int[] input1 = new int[] {17, 2, 3, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1};
        private int[] input2 = new int[] {5, 2, 2, 3, 3, 3, 3, 3};
        private int[] input3 = new int[] {8, 2, 5, 1, 3, 1, 1, 1, 1, 3, 1};
        private int[] input4 = new int[] {4, 3, 3, 2, 3, 1, 1};
        private int[] input5 = new int[] {1, 1, 1, 2};
        private int[] input6 = new int[] {11, 4, 2, 2, 2, 0, 7, 3, 2, 2, 4, 9, 1, 4};

        @SuppressWarnings("unused")
        @Mock
        int nextInt() throws IOException {
            int[] input = null;
            switch (InputCounter.inputNumber) { //THE WHOLE POINT HERE!
                case 1: input = input1; break;
                case 2: input = input2; break;
                case 3: input = input3; break;
                case 4: input = input4; break;
                case 5: input = input5; break;
                case 6: input = input6; break;
            }
            return input[InputCounter.pointer++];
        }
    };

    private static class InputCounter {
        public static byte inputNumber = 1;
        public static byte pointer = 0;

        public void switchInput(int number) {
            this.inputNumber = i;
            this.pointer = 0;
        }
    }

JMockit: howto invoke custom method of MockUp

2 Answers2