JUnit Testing: How To Test If Statements Without Missing A Branch?

Question

I have run EclEmma for coverage on my JUnit Test Cases and have reached up to 100% on some. However, on the ones that are 82% or 95% covered, there is a message next to my code that says "1 of 2 branches missed" and I can't seem to solve this issue.

After looking over my classes, I noticed that this message only appears next to my if-statements, and that is what's keeping my tests from being 100% covered.

I guess I'm asking if anyone knows how to test an if-statement in JUnit, so that neither branch is missed.

This is the code I'm trying to test:

private double height;
    public void setHeight(double height){
        if(height <=0){
            this.height = 0;
        }
        else{
            this.height = height;
        }
    }//method close

( I am using JUnit 4 )

Answer 1

Simple:

you want to have one distinct test case per path within your method under test; like:

• testSetHeightWithNegativeValue()
• testSetHeightWithZeroValue()
• testSetHeightWithPositiveValue

Each of them gives specific input to your method under test and checks for the expected output.

Where the real take away here is: consider thinking about your code. You should not need a coverage tool to figure that you need more tests for your method. Instead: you look at your method, and think what it is doing; and then you write testcases.

Coverage is fine to tell you that you did the right thing; but "doing the right thing" is what you should strive to do by yourself; and not to meet some numbers.

And, as the comments point out: consider using the TDD approach: when you write your tests before you create the "matching" piece of production code, then you make that "thinking" part an essential element of your working procedure.

Answer 2

Your code

public void setHeight(double height){
    if(height <=0){
        this.height = 0;
    }
    else{
        this.height = height;
    }
}

has two possible branches:

height <= 0

public void setHeight(double height){
     this.height = 0;
}

height > 0

public void setHeight(double height){
    this.height = height;
}

So in if statement, you can go to one statement or another in else . You have to create two unit tests to cover all possible ways - one for parameter passed height > 0 and second for height <= 0