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Question

I am getting 1/4 branch coverage when I run this JUnit test. However, when I change the if statement to "if (points == 1 || points == 2 || points == 3 || points == 4)" it passes the JUnit test. What am I doing wrong?

Main class:

public int getPoints() {
    return points;
}

public Grade(int p) throws IllegalArgumentException {
    if (p < 1 || p > 20)
        throw new IllegalArgumentException();
    points = p;
}

// Your additions/changes below this line

public Classification classify() {

    if (points >= 1 && points <= 4) {
        return Classification.First;
    }
    else {
        throw new IllegalArgumentException("Not a Grade");
    }
}

JUnit Test:

 @Test
 public void testFirst() {
    Assert.assertEquals(Classification.First, new Grade(1).classify());
    Assert.assertEquals(Classification.First, new Grade(2).classify());
    Assert.assertEquals(Classification.First, new Grade(3).classify());
    Assert.assertEquals(Classification.First, new Grade(4).classify());
}

Answer 1

A condition like this has 16 possible branches:

(a == 1 || b == 1 || c == 1 || d == 1)

with all of them false, all of them true, and all in between. The branch checker does not understand that

(points == 1 || points == 2 || points == 3 || points == 4)

has only 5 branches, because it does not analyze the relationship between the conditions.

Answer 2

Adding these additional tests to verify edge cases will increase your JUnit coverage to 4/4 for both the constructor and classify methods, at the cost of making a bunch of (possibly) worthless test cases, and also breaking data encapsulation (since you have duplicate validation checks in each of these methods).

@Test(expected = IllegalArgumentException.class)
public void TestSecond()
{
    new Grade(0).classify();
}

@Test(expected = IllegalArgumentException.class)
public void TestThird()
{
    new Grade(5).classify();
}

@Test(expected = IllegalArgumentException.class)
public void TestFourth()
{
    final Grade g = new Grade(1);
    g.points = 0;
    g.classify();
}

@Test(expected = IllegalArgumentException.class)
public void TestFifth()
{
    final Grade g = new Grade(1);
    g.points = 5;
    g.classify();
}