Parametrized Junit Tests: Postscript

In two earlier blog posts I commented on parametrized junit tests. This blog post will complement these post with an example of a piece of code.

Because all the important points are made in the other posts I will only present the Junit runner I created. A Maven project demonstrating this technique can be found code at my minimal examples repository

Without further ado: the Junit runner.

package org.junit.runners;

import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.junit.runner.Runner;
import org.junit.runner.notification.RunNotifier;
import org.junit.runners.Parameterized.Parameters;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.InitializationError;
import org.junit.runners.model.Statement;
import org.junit.runners.model.TestClass;

public class ParameterizedWithBuilder extends Suite
{
        private class TestClassRunnerForParametersWithBuilder extends BlockJUnit4ClassRunner
        {
                private final int fParameterSetNumber;

                private final List<Object> fParameterList;

                TestClassRunnerForParametersWithBuilder(Class<?> type, List<Object> parametersList, int i)
                        throws InitializationError
                {
                        super(type);
                        fParameterList = parametersList;
                        fParameterSetNumber = i;
                }

                @Override
                public Object createTest() throws Exception
                {
                        return getTestClass().getOnlyConstructor().newInstance(computeParams());
                }

                private Object computeParams() throws Exception
                {
                        try
                        {
                                return fParameterList.get(fParameterSetNumber);
                        }
                        catch (ClassCastException e)
                        {
                                throw new Exception(String.format("%s.%s() must return a Collection of objects.", getTestClass()
                                        .getName(), getParametersMethod(getTestClass()).getName()));
                        }
                }

                @Override
                protected String getName()
                {
                        return String.format("[%s]", fParameterSetNumber);
                }

                @Override
                protected String testName(final FrameworkMethod method)
                {
                        return String.format("%s[%s]", method.getName(), fParameterSetNumber);
                }

                @Override
                protected void validateConstructor(List<Throwable> errors)
                {
                        validateOnlyOneConstructor(errors);
                }

                @Override
                protected Statement classBlock(RunNotifier notifier)
                {
                        return childrenInvoker(notifier);
                }
        }

        private List<Runner> runners = new ArrayList<Runner>();

        public ParameterizedWithBuilder(Class<?> klass) throws Throwable
        {
                super(klass, Collections.<Runner> emptyList());
                List<Object> parametersList = getParametersList(getTestClass());
                for (int i = 0; i < parametersList.size(); i++)
                        runners.add(new TestClassRunnerForParametersWithBuilder(getTestClass().getJavaClass(), parametersList, i));

        }

        @Override
        protected List<Runner> getChildren()
        {
                return runners;
        }

        @SuppressWarnings("unchecked")
        private List<Object> getParametersList(TestClass testClass) throws Throwable
        {
                return (List<Object>) getParametersMethod(testClass).invokeExplosively(null);
        }

        private FrameworkMethod getParametersMethod(TestClass testClass) throws Exception
        {
                List<FrameworkMethod> methods = testClass.getAnnotatedMethods(Parameters.class);
                for (FrameworkMethod each : methods)
                {
                        int modifiers = each.getMethod().getModifiers();
                        if (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))
                                return each;
                }

                throw new Exception("No public static parameters method on class " + testClass.getName());
        }

}

Parametrized JUnit Tests Revisited

In the Parametrized JUnit Tests blog post I explained how to create a parametrized junit test. In this blog post I will discuss the reaction of one of my colleagues.

After reading my blog post about parametrized junit tests a colleague expressed his objections with this way of testing. He was a bit disappointed with one thing in particular. The signature of the public static method that is used to construct the test.

@Parameters
public static Collection<Object[]> data()

Is returns a collection of Object arrays. One Object array for each set of parameters. The reason this should be an Object array becomes clear from it's usage.

List<Object[]> data = new ArrayList<Object[]>();
data.add(new Object[] { 2, new Integer[] { 2 } });
return data;

Because the parameters used are of different type, in this case an Integer and an Integer array, they only super-type they have in common is Object.

The objection of my colleague was that is berefts the compiler of the oppertunity to detect type errors at compile time. The compiler would happily compile the following code. But it would blow up at run time.

List<Object[]> data = new ArrayList<Object[]>();
data.add(new Object[] { 2, new Integer[] { 2 } });
data.add(new Object[] { 2, new Double[] { 2.0 } });
return data;

After some discussion with my colleague we came up with the following solution. Instead of using a lot of parameters in the constructor, use only one. By using the builder pattern one retains the type information. Furthermore because now only one parameter is needed, the nearest super-type of all the parameters is the type of the parameter itself.

The code that follows show the same test as in the previous blog post. The change is reflected in the use of the builder pattern. Note that a fluent interface is used to easily construct a builder for the test.
One could still object that the array is now superfluous. They are correct. One way to deal with their objections is to write an custom runner.

@RunWith(Parameterized.class)
public class FactorizationTest
{
    private int number;

    private List<Integer> expectedResult;

    public FactorizationTest(FactorizationTestBuilder builder)
    {
        this.number = builder.getNumber();
        this.expectedResult = builder.getExpectedResult();
    }

    @Test
    public void factorize()
    {
        assertEquals(expectedResult, Factorization.factor(number));
    }

    @Parameters
    public static Collection<FactorizationTestBuilder[]> data()
    {
        List<FactorizationTestBuilder[]> data = new ArrayList<FactorizationTestBuilder[]>();
        data.add(new FactorizationTestBuilder[] { FactorizationTestBuilder.withNumber(2).expect(2) });
        data.add(new FactorizationTestBuilder[] { FactorizationTestBuilder.withNumber(8).expect(2, 2, 2) });
        data.add(new FactorizationTestBuilder[] { FactorizationTestBuilder.withNumber(9).expect(3, 3) });
        data.add(new FactorizationTestBuilder[] { FactorizationTestBuilder.withNumber(72).expect(2, 2, 2, 3, 3) });
        return data;
      }
}

class FactorizationTestBuilder
{
    private int number;

    private List<Integer> expectedResult = new ArrayList<Integer>();

    public static FactorizationTestBuilder withNumber(int number)
    {
        return new FactorizationTestBuilder(number);
    }

    private FactorizationTestBuilder(int number)
    {
        this.number = number;
    }

    public FactorizationTestBuilder expect(Integer... expectedResult)
    {
        this.expectedResult = Arrays.asList(expectedResult);
        return this;
    }

    public int getNumber()
    {
        return number;
    }

    public List<Integer> getExpectedResult()
    {
        return expectedResult;
    }
}

In this blog post I described the objections of a colleague on the previous Parametrized Junit Test blog. I have shown had to meet these objections by using the builder pattern.

Parametrized JUnit tests

In this post I will examine parametrized JUnit tests.

With the introduction of Junit 4, a lot has changed for testing Java software with Junit. One of the more esoteric additions are parametrized tests. It allows a developer to run a great deal of test which differ only in a set of parameters. Without further ado I will show you a parametrized test.

@RunWith(Parameterized.class)
public class FactorizationTest
{
    private int number;

    private List expectedResult;

    public FactorizationTest(int number, Integer[] result)
    {
        this.number = number;
        this.expectedResult = Arrays.asList(result);
    }

    @Test
    public void factorize()
    {
        assertEquals(expectedResult, Factorization.factor(number));
    }

    @Parameters
    public static Collection<Object[]> data()  
    {   
        List<Object[]> data = new ArrayList<Object[]>();
        data.add(new Object[] { 2, new Integer[] { 2 } });
        data.add(new Object[] { 8, new Integer[] { 2, 2, 2 } });
        data.add(new Object[] { 9, new Integer[] { 3, 3 } });
        data.add(new Object[] { 72, new Integer[] { 2, 2, 2, 3, 3 } });   
        return data;
    }
} 

Lets focus on line 17 of the method annotated with @Test. This method asserts that the expectedResult is returned by the static method Factorization.factor(int) which is called with parameter number. Both expectedResult and number are private fields of the class FactorizationTest. The fields are assigned in the constructor.

By annotating the class with the @RunWith(Parameterized.class) we are telling Junit to run this class with the Parameterized Runner. By implementing a Runner you can specify how to run the tests.

For the Parameterized this means the following. (The following section is paraphrased. See https://github.com/KentBeck/junit for the details.)

1. Get an Collection of Object-arrays.
2. Repeat for every Object-array in the collection:
   
   1. Construct an instance of FactorizationTest passing as parameters the various elements in the Object-array.
   2. Run all methods annotated with @Test.

The collection mentioned in step 1 is obtained by calling a method annotated with @Parameters. So in this example the following facts will be asserted.

number	factors
2	2
8	2, 2, 2
9	3, 3
72	2, 2, 2, 3, 3

In this blog post I made clear how to use parameterized test in the Junit test framework.