How to unit test a conversion library?

Question

I'm just starting out with unit testing in C#.
I have been reading about unit testing for a long time now, and I've already been playing around with NUnit, but this is the first time that I actually try to write real tests for real code.

But my problem is:
I'm having a hard time to come up with things that I can actually test.

The project I want to test is a conversion library (to convert lists of POCOs to ADO Recordsets).

So far, I've come up with only two things to test:

• if the recordset exists at all (not Null, not empty)
• if the content of each field is the same (--> if RS!Foo == POCO.Foo)

So, my questions are:

• What else can I test when my code just converts A to B?
• Or is this project too small / too simple / not a good example to write more than a few meaningful unit tests for?

Answer 1

Try the Pex tool from Microsoft. It generates Unit tests after analyzing your code. Just a quick install of Visual studio plugin. Then Right click the class/method you want to test and in the context menu get Pex to generate all the possible code paths for you.

Answer 2

There are quite a few things to test. I would also suggest thinking about and potentially verifying:

• Private fields of POCO don't map through correctly
• Invalid entries in the list throw exceptions correctly
• Recordset length is correct
• Inheritance in POCO is handled as desired (ie: base class members map through as expected)

Answer 3

Add a conversion test case where you know the exact input and output. Then test that the code produces that answer exactly.