How to add Jacoco Test Coverage static member variables?

Question

I have a class as follows:

public class XConstants { public static final int A_TYPE = 1; public static final int B_TYPE = 2; } 

I use both variables in my tests, but when I examine the test coverage with Jacoco, it shows% 0 to cover this class. I assume this is because I never instantiated this class, just use its static variables. I tried to create an instance, and the test coverage is% 100. How can I solve this problem?

Answer 1

JaCoCo measures test coverage based on the percentage of bytecode that was actually executed. Declaring a static final primitive or String constant does not generate bytecode to execute, it is just a record inside the constant pool. The only bytecode you have is an implicit default constructor, usually like this:

 aload_0 invokespecial Object.<init> return 

Therefore, when you do not name it, you have 0%, if you name it, you have 100%.

My suggestion is to ignore this problem. You should not try to achieve 100% coverage, no matter what. In the end, this does not guarantee anything: even 100% code can contain serious errors.

Answer 2

You created a class that can be created, but you never created it, so technically you did not use this code. A simple solution for a “class full of constants” is to make it an interface. Also note that the variables in the interface are public, static, and final by default, so your code might look something like this:

 public interface XConstants { int A_TYPE = 1; int B_TYPE = 2; } 

Answer 3

In our project, we overcome the problem of lack of coverage for a class containing only constants by creating a private constructor (the following template from java.lang.Math ):

 private XConstants {} 

and then using Trajano commons-testing to claim that this constructor is private and calls it to cover:

 assertUtilityClassWellDefined(XConstants.class) 

Answer 4

[Updated] jacoco 0.8.0 is configured by default, so you need to add a private constructor for it to work.