Mock Objects: Find Out Who Your Friends Are highlights the oft discussed criticisms of test driven development including: breaking encapsulation, hard to read, increased code fragility and whether it is a valuable use of developer time. Of course, these differences can be resolved in a typical XP way:
My point is that plenty of well-written code is produced without relying on mocks or Tell, Don’t Ask. On the other hand, I also encounter plenty of TDD novices who produce poor code and poor tests. Can Steve and Nat’s approach consistently help novices write better code and tests? It could be. At this point, I remain open minded and am ready to pair-program with Steve or Nat to learn more.
The second article, is about the studied effect of TDD on the quality of code, TDD: The Art of Fearless Programming. Pretty much every study showed an increased effort (15-60%) and an increase in quality (5-267%). The ratio of effort to quality is 1:2 - so it seems to pay. Example definitions of quality were "reduction in defects" or "increase in functional tests passing". In general:
All researchers seem to agree that TDD encourages better task focus and test coverage. The mere fact of more tests doesn’t necessarily mean that software quality will be better, but the increased programmer attention to test design is nevertheless encouraging. If we view testing as sampling a very large population of potential behaviors, more tests mean a more thorough sample. To the extent that each test can find an important problem that none of the others can find, the tests are useful, especially if you can run them cheaply.
Via Mock Objects