在 JUnit 上测试空值

Question

I am trying to test whether a user has entered the correct competition ID for a sport. Below is the method I have made for this:

protected boolean containCompetitionId (Set<RestrictionFailure> failures,  CompetitionSetup competitionId) {

    ScenarioDefinition.Competition competitionScenarioDef = new ScenarioDefinition.Competition();

    if (competitionScenarioDef.getId() == null) {
        failures.add(new RestrictionFailure("Competition ID does not exist", competitionId));
        return false;
    }
    else if(scenarioManager.findCompetitionById(competitionScenarioDef.getId()) == null) {
        failures.add(new RestrictionFailure("Competition ID does not exist", competitionId));
        return false;
    }
    else if(competitionScenarioDef.getId() != competitionId.getCompetitionId() ) {
        failures.add(new RestrictionFailure("Competition ID does not exist", competitionId));
        return false;
    }
    return true;
}

I want to make a Junit test for this method, how would I put a competition Id of value null in to my test and pass it on to the method i have made to test whether it generates the message ("Competition ID does not exist", competitionId) ?

Answer 1

You need to take advantage of dependency injection . It's a fancy name for a relatively simple concept. Essentially: do not create new objects within a method and, instead, have the caller of the method provide the object.

What you've seen observed is that by creating the object within the method, you have no control over how it's created, or what data it contains. This makes it difficult to test. Dependency injection solves this problem.

Your method would become:

protected boolean containCompetitionId (
    ScenarioDefinition.Competition competitionScenarioDef, // added
    Set<RestrictionFailure> failures,
    CompetitionSetup competitionId)
{

You can now inject any number of competitionScenarioDef s and test your method with any number of scenarios.

A test for this method might look somewhat like this. I've had to make up a few different things because you didn't provide code for all your classes (which is not necessarily a bad thing) so just think of it as pseudocode.

@Test
public void myTest()
{
    Foo foo = new Foo(); // whatever class contains your containCompetitionId method 

    Set<RestrictionFailure> failures = new HashSet<>();

    foo.containCompetitionId(
       new ScenarioDefinition.Competition(/*id: */ null)
       failures,
       new CompetitionSetup(...)
    );

    Assert.assertEquals(1, failures.size());
    Assert.assertEquals("Competition ID does not exist", failures.get().getFailureReason());
}

Answer 2

assertNull(Object actual) Asserts that actual is null. https://junit.org/junit5/docs/5.0.1/api/org/junit/jupiter/api/Assertions.html