“TDD done strictly from the
YAGNI principle leads to an
architectural meltdown
around iteration three.”
TDD YAGNI
3

“TDD done strictly from the
YAGNI principle leads to an
architectural meltdown
around iteration three.”
Bob Martin Jim Coplien
TDD YAGNI
3

Emergent Design is the process of evolving systems in
response to changing requirements, better
understanding of existing requirements, and in
response to new opportunities that arise from new
technology, better ideas, and a changing world.

©Artek ( http://www.artek.fi/ )

Context
Force
Facade Pattern
Solution
interface

1.
2.
3.
4.
5.
6.

• a test driven developer does not write a line of production
code until he has written a failing unit test, and no production
code can be written until there is a failing unit test
• you do not write more of a unit test than is sufficient to fail,
and “not compiling” is failing. So you cannot write very much
of the unit test before you must write production code;
• you cannot write more production code than is sufficient to
pass the currently failing test. So you cannot write a little bit of
a unit test and then run off and write a whole bunch of
production code.

( )

Refactoring
Green
Red
)
(

“TDD done strictly from the
YAGNI principle leads to an
architectural meltdown
around iteration three.”
Bob Martin Jim Coplien
TDD YAGNI
3

Emergent Design is the process of evolving systems in
response to changing requirements, better
understanding of existing requirements, and in
response to new opportunities that arise from new
technology, better ideas, and a changing world.

Refactoring
Green
Red
)
(

Refactoring
Green
Red
)
(

•
•
•
•