Junit-Quickcheck: Generate String matching a pattern

Question

I am using pholser's port. I have to generate strings matching a given pattern like \[a-zA-Z0-9\\.\\-\\\\;\\:\\_\\@\\[\\]\\^/\\|\\}\\{]* Length 40.

I extend the Generator class as:

public class InputGenerator extends Generator<TestData> {...}

It overloads a function:

publicTestData generate(SourceOfRandomness random, GenerationStatus status) {...}

Now, random has functions like nextDouble(), nextInt() but there is nothing for strings! How can I generate random strings matching the above pattern?

Answer 1

Find below snippet for a custom generator which implement the generate(..) method to return a random string matching your posted pattern.

public class MyCharacterGenerator extends Generator<String> {

    private static final String LOWERCASE_CHARS = "abcdefghijklmnopqrstuvwxyz";
    private static final String UPPERCASE_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String NUMBERS = "0123456789";
    private static final String SPECIAL_CHARS = ".-\\;:_@[]^/|}{";
    private static final String ALL_MY_CHARS = LOWERCASE_CHARS
            + UPPERCASE_CHARS + NUMBERS + SPECIAL_CHARS;
    public static final int CAPACITY = 40;

    public MyCharacterGenerator () {
        super(String.class);
    }

    @Override
    public String generate(SourceOfRandomness random, GenerationStatus status) {
        StringBuilder sb = new StringBuilder(CAPACITY);
        for (int i = 0; i < CAPACITY; i++) {
            int randomIndex = random.nextInt(ALL_MY_CHARS.length());
            sb.append(ALL_MY_CHARS.charAt(randomIndex));
        }
        return sb.toString();
    }
}

edit A simple unit test to demonstrate the usage of the MyCharacterGenerator class.

import com.pholser.junit.quickcheck.ForAll;
import com.pholser.junit.quickcheck.From;
import static org.junit.Assert.assertTrue;
import org.junit.contrib.theories.Theories;
import org.junit.contrib.theories.Theory;
import org.junit.runner.RunWith;

@RunWith(Theories.class)
public class MyCharacterGeneratorTest {

    @Theory
    public void shouldHold(@ForAll @From(MyCharacterGenerator.class) String s) {
        // here you should add your unit test which uses the generated output
        // 
        // assertTrue(doMyUnitTest(s) == expectedResult);

        // the below lines only for demonstration and currently
        // check that the generated random has the expected
        // length and matches the expected pattern
        System.out.println("shouldHold(): " + s);
        assertTrue(s.length() == MyCharacterGenerator.CAPACITY);
        assertTrue(s.matches("[a-zA-Z0-9.\\-\\\\;:_@\\[\\]^/|}{]*"));
    }
}

sample output generated by shouldHold

shouldHold(): MD}o/LAkW/hbJVWPGdI;:RHpwo_T.lGs^DOFwu2.
shouldHold(): IT_O{8Umhkz{@PY:pmK6}Cb[Wc19GqGZjWVa@4li
shouldHold(): KQwpEz.CW28vy_/WJR3Lx2.tRC6uLIjOTQtYP/VR
shouldHold(): pc2_T4hLdZpK78UfcVmU\RTe9WaJBSGJ}5v@z[Z\
...