Add test coverage instructions

[Jagrutiti]

Add test coverage instructions

Adding instructions to understand test coverage in CONTRIBUTING.md

As a newbie, I was confused to get to the bottom of it. Here I am documenting the steps that helped me.

[Jagrutiti]

Here I do not know what the orange color means. That is why I have not added anything about it.

I was thinking of adding screenshots. But then thought against it. The instructions will help someone understand what is happening unless any of the steps change in the future.

[MarkEWaite]

The orange color means that one or more of the paths through that statement have not been executed.

Consider the following statement:

 String name = importantArgument != null ? importantArgument.getName() : "unknown name";

There are two paths in that statement, one when importantArgument is null and one when it is not null. If the statement is never called with importantArgument as null, then the line will be colored orange to indicate that at least one path is not covered.

If you prefer a more automatic way of viewing the results, you could configure a Jenkins job that uses the JaCoCo plugin to display the results within a Jenkins job. You can see that in a job definition that I maintain.

[MarkEWaite]

Thanks for the contribution! The Windows example needs a change, but otherwise that looks good

[MarkEWaite]

The orange color means that one or more of the paths through that statement have not been executed.

Consider the following statement:

 String name = importantArgument != null ? importantArgument.getName() : "unknown name";

There are two paths in that statement, one when importantArgument is null and one when it is not null. If the statement is never called with importantArgument as null, then the line will be colored orange to indicate that at least one path is not covered.

If you prefer a more automatic way of viewing the results, you could configure a Jenkins job that uses the JaCoCo plugin to display the results within a Jenkins job. You can see that in a job definition that I maintain.