Question

I have a piece of java code which reads strings from a file and creates a map out of the strings. As this code depends on a file, unit testing is clumsy. How does one design such pieces so that code can be unit tested?

One approach that I can think of is, instead of this piece taking a file as an argument it can take an input stream. In actual scenario, pass the file input stream, while unit testing pass an input stream created from a string. But, this looks like an over kill to me. Is there a better way?

Answer 1

Look at it this way: no matter how you reorganize your code, the test data has to come from some file. I see 2 variants:

1. Data is encoded in-place, in one of the .java unit test source code files. It works only for small test data sets. You would need to refactor your code to take input stream and have another wrapper that works with file, as you described.

2. Test data file. You have to create a
   project-wide convention where to keep your test
   data files. Their location may be
   relative to the jave project
   location, or under a common test
   data files root. In any case, it helps
   to have a utility method that
   returns a full test data file path given a “logical” file name.

It seems like in your case (just one test, a hundred words) the first solution may be enough. Yes, you would need to refactor the code a little. The second solution is more generic and personally I find it much more practical and applicable.

Some people would say this is not a unit test if it works with data files. Well, it’s a matter of definition of “unit test”, and is quite irrelevant. If you need to test your code, just find the best / most convenient way for your project.