Unit Tests

Can somebody explain unit testing and test driven development? I've tried to learn it through blogs and code samples and such, but I just can't grasp it. It seems like a really backwards way of writing code. I've never really had a problem learning all kinds of programming concepts and methodologies in the past but this stumps me. Is it supposed to be a really difficult thing to learn or am I just retarded?

>>15
I happen to have read PM up to page 130 or something, and it is enough to understand the notation. Do you know how remarkably simple this 'theorem' is? It says that if both a and b are '1', but not the same '1', then their union is '2'.

You can think of a = i'x as a being a set of cardinality one. Basically it says that a \cap b = 0 <=> x != y.

Russel thought his work was more important than it really were, that's why he goes through great length of doing things at times, when it isn't necessary.