to make sure no one by mistake initializes an instance of this class
Usually what I do, is to change the method/constructor from private to default package visibility. And I use the same package for my test class, so from the test the method/constructor is accessible, even if it is not from outside.
To enforce the policy to not instantiate the class you can:
- throw UnsupportedOperationException("don't instantiate this class!") from the default empty constructor.
- declare the class abstract: if it only contains static methods, you can call the static methods but not instantiate it, unless you subclass it.
or apply both 1+2, you can still subclass and run the constructor if your test shares the same package as the target class.
This should be quite "error proof"; malicious coders will always find a workaround :)
