Divide and conquer

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h4. Divide et impera - architecture, implementation and tests

In JigZaw context, "_Divide and conquer_" is the concept of dividing a problem into sub-problems until we know how to solve them. This is a well-known technique for handling something complex and/or complicated. This principle is the cornerstone of the test strategy and is the origin for the name JigZaw. _Jigsav puzzles_ got their name from a painting divided into small pieces with a jigsaw. The same as we do to a complicated test problem; we split it into multiple smaller problems.

Divide and conquer can be applied the test code, but also on the architecture and the actual implementation code. A typical example of applying this principle is to refactor a [God object|http://en.wikipedia.org/wiki/God_object] and write separate tests for each of the concerns the God object was split into.

JigZaw promotes the concept of using _tests to drive the development_, but the recommended process is more sophisticated than the [test-first|http://www.extremeprogramming.org/rules/testfirst.html] principle recommended by eXtreme Programming and TDD. The first part of David Heinemeier Hansson's blogpost [TDD is dead. Long live testing.|http://david.heinemeierhansson.com/2014/tdd-is-dead-long-live-testing.html] explains some of our objections to the test-first approach.

* [Single-responsibility principle]
* Intention Revealing Interface, see Domain-driven Design: Tackling Complexity in the Heart of Software by Eric Evans.


h6. Maven multi-module antipattern?

For maven users, it is useful to reflect over how _maven multi-module_ break the concept by allowing several pieces in the puzzle to be altered simultaneously. Unfortunately, the world is not perfect, so you can't have complete freedom and self-standing quality modules at the same time (the truth holds both for development and in the real world).

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h4. Historical references and quotes

The divide and conquer tactic is perhaps best known from [Divide and conquer algorithms | http://en.wikipedia.org/wiki/Divide_and_conquer_algorithm] or the political [Divide and rule | http://en.wikipedia.org/wiki/Divide_and_rule] - _divide et impera_ - strategy.

h6. Quotes on Complexity

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