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Unit Testing a Private Method

So on a lark, I threw my hat into the ring for Portland Code Camp 2.0, I didn’t expect to get accepted, there were already a few sessions on unit testing and nunit but I figured, what the heck, let’s gear it for beginners, and do it in VB.Net.  Now I’m in the process of getting ready and I figured I should blog about things and or techniques as they came up.

For my first trick, testing a private method.

First rule of thumb: Don’t do this.

No really, Don’t.

You are locking the internals of your code down with your unit test, if you are having to test a private method, then chances are that method should be public on a different class.

However, if you are sitting in a situation where that kind of refactoring is just not going to be allowed and you still really-really-need-to-get-this-under-test, then this simple process can help.


Private Function Add2Integers(byval x as integer, byval y as integer) as integer

    return x + y

End Function

You want to get this under test, but you want this to be a refactor (which is NOT another word for maintenance, it’s a word for code clean up, not feature changing) which means no changes as far as the users are concerned.

Try this, wrap the code in a compiler conditional, and then just call the function, and then pass the value back out.

Now your unit tests can access the private method.

#If DEBUG Then

Public Function public_Add2Integers(byval x as integer, byval y as integer) as integer

return Add2Integers( x, y) as integer

End Function

One more time, really, don’t do this, if you are not REALLY careful, this will come back and bite you hard.

This article is part of the GWB Archives. Original Author: Geekus Con Livus

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