Presented at SwanseaCon (2017-09-26) We default to considering systems from an insider's perspective; the view from outside can be quite different. Can we apply this inversion to more than just requirements? We may say we want testing, but what do we want from testing? We may say we want logging, but what do we want from logging? We may say we want clean code, but what do we want from clean code? We may say we want an agile process, but what do we want from an agile process? These are harder questions, but their answers can make for better solutions.

1. Turning
Development
Outside–In
@KevlinHenney

2. What We Talk About
When We Talk About
Development
@KevlinHenney

3. What We Talk About
When We Talk About
Requirements
@KevlinHenney

5. Too often we push the problem
into the background because we
are in a hurry to proceed to a
solution.

6. If you read most software
development texts thoughtfully,
you will see that almost everything
is about the solution; almost
nothing is about the problem.

7. Analysis Design Code Test

8. Analysis Design Code Test

9. Analysis Design Code Test

10. It's expensive to
know everything
up front.
Kolton Andrus

11. You have to finish things —
that's what you learn from,
you learn by finishing things.
Neil Gaiman

12. SCRUM: A Pattern
Language for
Hyperproductive
Software
Development Teams
Mike Beedle, Martine Devos,
Yonat Sharon,Ken Schwaber,
and Jeff Sutherland

13. SCRUM Master
Sprint
Backlog
SCRUM Meetings
Demo After Sprint
SCRUM Master
Sprint
Backlog
SCRUM Meetings
Demo After Sprint

14. Problem
You want to balance the needs of developers to work
undisturbed and the needs of management and the
customer to see real progress, as well as control the
direction of that progress throughout the project.
Solution
Divide the project in Sprints. A Sprint is a period of
approximately 30 days in which an agreed amount of
work will be performed to create a deliverable. Each
Sprint takes a pre-allocated amount of work from the
Backlog.
Sprint

15. Analysis
Sprint
Design
Sprint
Code
Sprint
Test
Sprint

16. Analysis
Design
Code
Test
Analysis
Design
Code
Test
Analysis
Design
Code
Test
Analysis
Design
Code
Test

17. Develop Develop Develop Develop

18. Develop

20. If a plot works out exactly
as you first planned, you're
not working loosely enough
to give room to your
imagination and instincts.

21. / WordFriday

22. pantser, noun
▪ Writer who writes by the seat of their pants.
▪ In contrast to a plotter, a pantser doesn't
work to (or have) an outline.

24. Your Customers
Do Not Mean
What They Say
Nate Jackson

25. I’ve never met a customer yet that
wasn’t all too happy to tell me what
they wanted—usually in great detail.
The problem is that customers don’t
always tell you the whole truth.
Nate Jackson

26. They generally don't lie.
They use their terms and their contexts.
They leave out significant details.
They make assumptions.
Nate Jackson

27. This is compounded by the fact that
many customers don’t actually know
what they want in the first place!
Nate Jackson

28. Systems have properties
— capabilities, features,
characteristics, etc. —
inside and out.

29. Development should
discover the specific
properties desired
and make them so.

31. ▪
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▪

32. ▪
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▪
▪

33. ▪
▪
▪
▪
▪
▪

34. ▪
▪
▪
▪
▪
▪

35. ▪
▪
▪
▪
▪
▪
Try to leave
out the part
that readers
tend to skip.
Elmore Leonard

36. ▪
▪
▪

37. ▪
▪
▪

39. Stack
{new, push, pop, depth, top}

40. Given
When
Then
an empty stack
an item is pushed
it should not be empty

41. Given
When
Then
an empty stack
an item is pushed
if it's OK with you, I
think that, perhaps, it
should probably not be
empty, don't you think?

42. Omit needless words.
William Strunk and E B White
The Elements of Style

43. Make definite assertions.
Avoid tame, colourless, hesitating, noncommittal
language.
When a sentence is made stronger, it usually becomes
shorter. Thus brevity is a by-product of vigour.
William Strunk and E B White
The Elements of Style

44. Given
When
Then
an empty stack
an item is pushed
it is not empty

45. Given
When
Then
And
an empty stack
an item is pushed
it has a depth of 1
the top item is the item
that was pushed

46. Given_an_empty_stack_Wh
en_an_item_is_pushed_Th
en_it_has_a_depth_of_1_
And_the_top_item_is_the
_item_that_was_pushed

47. Non-EmptyEmpty
depth depth
top
push
pop [depth > 1]
push
pop [depth = 1]
new

48. public class Stack_spec
{
public static class A_new_stack
{
@Test
public void is_empty() 
}
public static class An_empty_stack
{
@Test()
public void throws_when_queried_for_its_top_item() 
@Test()
public void throws_when_popped() 
@Test
public void acquires_depth_by_retaining_a_pushed_item_as_its_top() 
}
public static class A_non_empty_stack
{
@Test
public void becomes_deeper_by_retaining_a_pushed_item_as_its_top() 
@Test
public void on_popping_reveals_tops_in_reverse_order_of_pushing() 
}
}

49. public class
Stack_spec
{
public static class
A_new_stack
{
@Test
public void is_empty() 
}
public static class
An_empty_stack
{
@Test()
public void throws_when_queried_for_its_top_item() 
@Test()
public void throws_when_popped() 
@Test
public void acquires_depth_by_retaining_a_pushed_item_as_its_top() 
}
public static class
A_non_empty_stack
{
@Test
public void becomes_deeper_by_retaining_a_pushed_item_as_its_top() 
@Test
public void on_popping_reveals_tops_in_reverse_order_of_pushing() 
}
}

50. public class
Stack_spec
{
public static class
A_new_stack
{
@Test
public void is_empty() 
}
public static class
An_empty_stack
{
@Test()
public void throws_when_queried_for_its_top_item() 
@Test()
public void throws_when_popped() 
@Test
public void acquires_depth_by_retaining_a_pushed_item_as_its_top() 
}
public static class
A_non_empty_stack
{
@Test
public void becomes_deeper_by_retaining_a_pushed_item_as_its_top() 
@Test
public void on_popping_reveals_tops_in_reverse_order_of_pushing() 
}
}

51. Systems have properties
— capabilities, features,
characteristics, etc. —
inside and out.

53. Functional
Operational
Developmental

54. We want our code
to be unit testable.
What is a unit test?

55. A test is not a unit test if:
▪ It talks to the database
▪ It communicates across the network
▪ It touches the file system
▪ It can't run at the same time as any of your other
unit tests
▪ You have to do special things to your environment
(such as editing config files) to run it.
Michael Feathers
http://www.artima.com/weblogs/viewpost.jsp?thread=126923

56. A unit test is a test of behaviour
whose success or failure is wholly
determined by the correctness of
the test and the correctness of the
unit under test.
Kevlin Henney
http://www.theregister.co.uk/2007/07/28/what_are_your_units/

57. What do we want
from unit tests?

58. When a unit test
passes, it shows
the code is correct.

59. When a unit test
fails, it shows the
code is incorrect.

60. As a
I want
So that
$Role
$Feature
$Benefit

61. As a
I want
So that
developer of the software
$Feature
$Benefit

62. As a
I want
So that
developer of the software
clean code
$Benefit

63. As a
I want
So that
customer of the software
$Feature
$Benefit

64. As a
I want
So that
user of the software
$Feature
$Benefit

65. As a
I want
So that
$Role
logging
$Benefit

66. As a
I want
So that
developer of the software
logging
$Benefit

67. As a
I want
So that
customer of the software
logging
$Benefit

68. As a
I want
So that
$Role
documentation
$Benefit

69. As a
I want
So that
$Role
an agile process
$Benefit

70. As a
I want
So that
As shown by
$Role
$Feature
$Benefit
$Evidence

72. Design an architectural
space to accommodate
a specific program,
experience, or intent.