What is a really simple explanation of unit testing?

Question

I've never done any unit testing before, and would like to learn what it is and how it can be useful in my Python code.

I've read through a few Python unit testing tutorials online but they're all so complicated and assume an extended programming background. I'm using Python with Pylons to create a simple web app.

Any simple examples would be greatly appreciated.

Thanks!

Answer 1

Consider this.

Here's a class we've written.

class Something( object ):
    def __init__( self, a, b ):
        self.a= a
        self.b= b
    def sum( self ):
        return self.a+self.b+self.a

That's a test for that class.

import unittest
class TestSomething( unittest.TestCase ):
    def setUp( self ):
        self.s = Something( 1, 2 )
    def test_should_sum( self ):
        self.assertEquals( 3, self.s.sum() )

if __name__ == "__main__":
    unittest.main()

Does the class -- as a stand-alone unit -- pass the test?

If not, what's the bug?

We've taken the class -- as a stand-alone unit -- and tested it. That's unit testing.