This document discusses using duck-typing and state machines to understand requirements and develop software. It emphasizes that what matters most is how the end result "quacks" or behaves, not what technologies are used. State machines can model requirements as a set of possible states and transitions between them. Behavior-driven development tests can verify that the system meets requirements by specifying scenarios in the given/when/then format. Overall, the document stresses focusing on understanding why something needs to be developed rather than how, and using patterns like state machines and tests to manage complexity and deliver expected behavior.

1. ⚙⚙🦆

2. ?? ?????
???? at Atlassian

3. 1
the first problem to solve

5. Man
Camera

7. Anton Korzunov
Cameraman at Atlassian

8. QUACK!
QUACK!
QUACK!
QUACK!

9. What The Duck
Warning! It’s so easy to misspell it!

10. Suppose you see a bird walking around in a farm yard.
This bird has no label that says 'duck'. But the bird
certainly looks like a duck. Also, he goes to the pond
and you notice that he swims like a duck. Then he
opens his beak and quacks like a duck. Well, by this
time you have probably reached the conclusion that
the bird is a duck, whether he's wearing a label or not.
Richard Cunningham Patterson Jr., 1950

11. It does not matter
What it “is”. It is only matters
how it “quacks”
If it quacks
Then you can handle it
The Point Is…

12. And you are expected to known
EVERYTHING about 🦆.
That’s quite naive :P

13. 2
the second problem to solve

14. Compliances
Your thing is compliant, if all
checkboxes swims like a
compliance.
Duck species
Patterns
How to recognise a pattern?
Well - every pattern quacks
differently.
Standards
Your thing is “according to the
standards”, if it walks like a
standard.

15. You duck!
The real problem for all developers

16. The Goal
the goal of any development is not to
develop something, but develop A
THING.

17. It’s hard to
understand
the
requirements

18. It’s hard to
understand
the
requirements

19. Blah-Blah,
3 wishes

20. I WANT TO
BE RICH!

22. !!!YOU ARE
RICH!!!
Everybody hates
you
And you are a 🦆

23. The evil jinn
will try to
revenge his
enslaver

24. good systems must
meet simultaneously
a number of
requirements;
therefore, they are
more fragile
Catastrophe Theory
"The Principle of
Fragility of Good
Things

25. Rich
So you can buy a
new iPhone
(every year)
iPhone
cos all cool guys
have the latest
iPhone!
Cool
Because people
respect cool guys?
Respect?
Respect has nothing
with everything
before…
Why?

27. I WANT TO
BE RICH!
WHAT YOU
REALLY
NEED?

28. Good Taste?
Good Smell?
Good Look?

29. In other words - not the every
“Men With A Camera” is a
“Photograph”.
Having a 📸 is not enough, 😢

30. Man
Camera

31. The Artist
Image capturing
tool
💩

32. Having React
Having Redux
Having TypeScript
Having GraphQL
- is not enough

33. IT DOES NOT MATTER
What it “is”. It is only matters how it
“quacks”
If it quacks
Then you can handle it
The Point Is…

34. JFYI - That Evil Djinn is you

35. BDD
Behaviour Driven Development

36. Given: The same
Page
When: I am
authorised
Then: I could see
my face
Given: A Page
When: I click The
Button
Then: 🙀
USER SCENARIO
#1
USER SCENARIO
#2

37. Given: The same
Page
When: I am
authorised
Then: I could see
my face
Given: A Page
When: I click The
Button
Then: 🙀
USER SCENARIO
#1
USER SCENARIO
#2
QUACK!
QUACK!
QUACK!
QUACK!

38. Given: The same
🦆
When: It swims
Then: It swims like
another 🦆
Given: A 🦆
When: It walks
Then: It walks like
another 🦆
USER SCENARIO
#1
USER SCENARIO
#2

39. Quacks like a
good App?
I guess it
was a good
App!

40. All happy
families are
alike; each
unhappy
family is
unhappy in
its own way.
Principle

41. All happy 🦆
quacks the
same
Principle

42. Given:
Advertisement
When: I click it
Then: 🤑
Given: No
payments
When: I provide
payments
Then: 🤑
USER SCENARIO
#3
USER SCENARIO
#4

44. 🦆 is a Destination

45. Given:
Advertisement
When: I click it
Then: 🤑
Given: No
payments
When: I provide
payments
Then: 🤑
USER SCENARIO
#3
USER SCENARIO
#4
SLI&
metrics

46. There is a Duck.
It does not Quack.
You kick the Duck
Quack! Quack!
(😌 the Duck is alive)
🧞:dont test implementation details

47. Triage

48. GP “ducks”
you against
known illness
patterns
Triage is the process
of determining the
priority of patients'
treatments based on
the severity of their
condition
TRIAGE GP DOES TRIAGE

49. Decision Tree

50. 🦆 👉 quack 👉 🦆
repeat

51. Given 👉 When 👉 Then
repeat

52. A low level
duck
“transition”
Probably “the state”
A high level
duck
“transition”
Some “process”
⚙
(BIG MACHINE)
⚙
(SMALL MACHINE)

53. A pattern to match. A way to
recognise the internal state by
observing the outer one.
A state of one or more than
one(!) State Machine.
DUCK

54. In terms of React component - Duck
is a combination of props.
Well, it’s always a combination of
some information you might
“observe”.
Let’s call it “signs”.
DUCK

56. Is a behaviour matching one of
the known 🦆.
Something “passing” the Duck
Typing.
DUCKS / DUCKING LIKE / QUACKS

57. Is a “journey” from one 🦆 to
another 🦆.
👉Button is now “disabled”? Ducks like a
Form transition from “Idle” to “Submitting”
TRANSITION

58. State Machines
Only a sith deals in absolutes

60. XState
State Charts with
visualisation
SDL/UML
Were a big thing
10-20 years ago
Flow
How multiple
systems are
connected
Automatos
“table state
machines” and flow
diagrams
State Machinery

61. State Charts

62. SDL

63. Timing/Flow Diagrams

64. Timing/Flow Diagrams
Network requests between different Services
Messaging between Layers
useEffect plays ping-pong

65. State Transition Table

66. State Transition Table

67. Redux

68. XFlow
On event do
something
SDL
On event do
something
Flow
On event do
something
Automatos
On event do
something
State Machinery
🦆
👉
quack
👉
🦆

69. It does not matter
Which technology you use, it matters how
you use it. But still just a bit.
The only Real Thing, the most important
one - how the result “quacks”.

70. 👉Finite👈 State Machines
Commit to your commitments
Known your possibilities
Even better - document them

71. Oh wow!
So much!
🤯

72. 3
third problem to solve

73. !!!!
How disabled pressed button should
look like
????
Could be button be disabled and
focused?

75. Great Green Dragon?
opinion-size-age-shape-colour-
origin-material-purpose Noun.
So you can have a lovely little old
rectangular green French silver whittling
knife. But if you mess with that word
order in the slightest you’ll sound like a
maniac. It’s an odd thing that every
English speaker uses that list, but almost
none of us could write it out. And as size
comes before colour, green great
dragons can’t exist.

76. React is a
Fiction

77. For every
Quack
should be a
Duck

78. No mutants
allowed
/
Beware of
the evil Djinn

79. Wrapping up

80. Hey! Where is JS?
Writing code is the easiest part of your job.
Writing the correct code is much harder.
Making your application work “right” is not even
possible.

81. Blind men
and an
elephant

82. Every Test
And every Duck
Is a “Blind Man”.
Given 👉 When 👉 Then
And your App is an Elephant

83. Allegory of
the cave

84. All you can see are shadows/
there is no spoon
UI is a combination of multiple
unrelated pieces
<Button/> is nothing more than
pixels, which ducks familiar…

85. Think in
Flows and
Processes.
⚙ and ⚙
You don’t
have to use
state
machines to
use them
ONE SIDE THE OTHER SIDE

86. Don’t think what to do.
Don’t think how to do.
Think why to do.
(and think what have
you done)
The code does not
matter.
Your ability to
understand the
code - matters
ONE SIDE THE OTHER SIDE

87. QA/QE/Manager
is your friend.
- Try to convert their language into the
duck-test (BDD).
- Then create an Elephant(State
Machine) passing these tests.
- Then – code.

88. Requirement
A business “requirement”,
that Where👉When👉Then,
which, well, quacks…
Quacks like a real thing you
were asked to do.
It is a test for a test.
State Machine
Which explains what
this thingy does, and
how.
As well as verify and
enforce it.
Test
Which tests the code
The code
Which actually works
There are…

89. When the change came
- where would be a 🦆,
- which “quack”
- and no more “unexpected
consequences”
- no more “surprises”

90. You have mastered it.
Now you know what you are
doing
😌

91. Read more at