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@sandimetz Apr 2013
The Magic Tricks of
Testing
Sandi Metz
Saturday, April 27, 13
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@sandimetz Apr 2013
Why do
I hate my tests?
Saturday, April 27, 13
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@sandimetz Apr 2013
Why do
I hate my tests?
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@sandimetz Apr 2013
They’re slow
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@sandimetz Apr 2013
They’re fragile
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@sandimetz Apr 2013
They’re expensive
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@sandimetz Apr 2013
They are misery
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@sandimetz Apr 2013
They are misery
incarnate
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@sandimetz Apr 2013
It doesn’t have to be
this way
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@sandimetz Apr 2013
Just delete some tests
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@sandimetz Apr 2013
Unit Tests: Goals
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@sandimetz Apr 2013
Thorough
Unit Tests: Goals
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@sandimetz Apr 2013
Thorough
Stable
Unit Tests: Goals
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@sandimetz Apr 2013
Thorough
Stable
Fast
Unit Tests: Goals
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@sandimetz Apr 2013
Thorough
Stable
Fast
Few
Unit Tests: Goals
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@sandimetz Apr 2013
How does your app
feel?
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@sandimetz Apr 2013
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@sandimetz Apr 2013
Focus on messages
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@sandimetz Apr 2013
Objects are
simple-minded
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@sandimetz Apr 2013
Object
Under
Test
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@sandimetz Apr 2013
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@sandimetz Apr 2013
Object
Under
Test
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@sandimetz Apr 2013
Object
Under
Test
Received from
others
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@sandimetz Apr 2013
Object
Under
Test
Received from
others
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@sandimetz Apr 2013
Object
Under
Test
Incoming
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@sandimetz Apr 2013
Sent to
others
Incoming
Object
Under
Test
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@sandimetz Apr 2013
Sent to
others
Incoming
Object
Under
Test
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@sandimetz Apr 2013
Incoming Outgoing
Object
Under
Test
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Object
Under
Test
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Object
Under
Test
Saturday, April 27, 13
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@sandimetz Apr 2013
Incoming
Sent to Self
Outgoing
Message Origin
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Object
Under
Test
Saturday, April 27, 13
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Object
Under
Test
Saturday, April 27, 13
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Object
Under
Test
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@sandimetz Apr 2013
Sent to self
Incoming Outgoing
Query Command
Object
Under
Test
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@sandimetz Apr 2013
Query
Command
Message Type
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@sandimetz Apr 2013
Query: Return something/
change nothing
Command: Return nothing/
change something
Type
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@sandimetz Apr 2013
Query: Return something/
change nothing
Command: Return nothing/
change something
Type
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@sandimetz Apr 2013
Query: Return something/
change nothing
Command: Return nothing/
change something
Type
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@sandimetz Apr 2013
We conflate
commands and queries
at our peril
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@sandimetz Apr 2013
but
we do it all the time
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Query Command
Message Origin x Type
Outgoing
Incoming
Type
Origin
@sandimetz Apr 2013
Message
Sent to Self
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Part 1
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Incoming
Query Messages
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Incoming
Wheel
diameter
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Wheel
attr_reader
:rim,
:tire
def
initialize(rim,
tire)
#
...
end
def
diameter
rim
+
(tire
*
2)
end
#
...
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Wheel
attr_reader
:rim,
:tire
def
initialize(rim,
tire)
#
...
end
def
diameter
rim
+
(tire
*
2)
end
#
...
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Wheel
attr_reader
:rim,
:tire
def
initialize(rim,
tire)
#
...
end
def
diameter
rim
+
(tire
*
2)
end
#
...
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
WheelTest
<
MiniTest::Unit::TestCase
def
test_calculates_diameter
wheel
=
Wheel.new(26,
1.5)
assert_in_delta(29,
wheel.diameter,
0.01)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
WheelTest
<
MiniTest::Unit::TestCase
def
test_calculates_diameter
wheel
=
Wheel.new(26,
1.5)
assert_in_delta(29,
wheel.diameter,
0.01)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
WheelTest
<
MiniTest::Unit::TestCase
def
test_calculates_diameter
wheel
=
Wheel.new(26,
1.5)
assert_in_delta(29,
wheel.diameter,
0.01)
end
end
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@sandimetz Apr 2013
Rule
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@sandimetz Apr 2013
Test incoming query messages
Rule
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@sandimetz Apr 2013
Test incoming query messages
by making assertions
about what they send back
Rule
Saturday, April 27, 13
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Query Command
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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Query Command
Assert
result
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Incoming
Another
Incoming
Query Message
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
gear_inches
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Wheel
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@sandimetz Apr 2013
Sight along the edges of
the space capsule
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@sandimetz Apr 2013
Sight along the edges of
the space capsule
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
Test the interface
Saturday, April 27, 13
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@sandimetz Apr 2013
Test the interface
(not the implementation)
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Incoming
Command Messages
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
set_cog
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_set_cog
gear
=
Gear.new
gear.set_cog(27)
assert(27,
gear.cog)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_set_cog
gear
=
Gear.new
gear.set_cog(27)
assert(27,
gear.cog)
end
end
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_set_cog
gear
=
Gear.new
gear.set_cog(27)
assert(27,
gear.cog)
end
end
Send the message
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_set_cog
gear
=
Gear.new
gear.set_cog(27)
assert(27,
gear.cog)
end
end
Assert the side effect
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@sandimetz Apr 2013
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Test incoming command messages
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Test incoming command messages
by making assertions
about direct public side effects
Rule
Saturday, April 27, 13
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Query Command
Assert
result
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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Query Command
Assert
result
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Assert
direct public
side effects
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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@sandimetz Apr 2013
DRY It Out
Saturday, April 27, 13
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@sandimetz Apr 2013
Receiver of incoming message
has sole responsibility
DRY It Out
Saturday, April 27, 13
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@sandimetz Apr 2013
Receiver of incoming message
has sole responsibility
for asserting
the result
direct public side effects
DRY It Out
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Part 2
to Self
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Messages Sent to Self
to Self
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Anti-Pattern
to Self
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_ratio
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(4.7,
gear.ratio,
0.01)
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_ratio
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(4.7,
gear.ratio,
0.01)
end
Test the private method?
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_ratio
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(4.7,
gear.ratio,
0.01)
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_ratio
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(4.7,
gear.ratio,
0.01)
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_ratio
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(4.7,
gear.ratio,
0.01)
end
Redundant:
#gear_inches test is proof enough
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Anti-Pattern
to Self
Incoming
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
Gear
#
...
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
end
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.expect(:ratio)
gear.verify
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.expect(:ratio)
gear.verify
end
Expect to send
the private method?
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.expect(:ratio)
gear.verify
end
Over Speci ed:
Adds no safety yet
breaks with every change
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@sandimetz Apr 2013
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Do not test private methods
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Do not test private methods
Do not make assertions about their result
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Do not test private methods
Do not make assertions about their result
Do not expect to send them
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Break rule if it saves $$$
during development
Caveat
Saturday, April 27, 13
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Query Command
Assert
result
Assert
direct public
side-effects
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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Query Command
Assert
result
Assert
direct public
side-effects
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Ignore
Message
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Part 3
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Outgoing
Query Messages
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Spoiler Alert
Same rules as ‘Sent to Self’
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
diameter
Gear
gear_inches
Wheel
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
gear_inches
ratio
*
wheel.diameter
end
private
def
ratio
chainring
/
cog.to_f
end
#
...
end
Wheel
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@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
Gear
Outgoing
Wheel
diameter
Incoming
Query
gear_inches
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Anti-Pattern
to Self
Incoming to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
assert_in_delta(29,
gear.wheel.diameter,
0.01)
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
assert_in_delta(29,
gear.wheel.diameter,
0.01)
end
end
Assert result of
outgoing query?
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
assert_in_delta(29,
gear.wheel.diameter,
0.01)
end
end
Redundant:
Duplicates Wheel’s tests
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Anti-Pattern
to Self
Incoming to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.wheel.expect(:diameter)
gear.verify
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.wheel.expect(:diameter)
gear.verify
end
end
Expect to send
outgoing query?
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_calculates_gear_inches
gear
=
Gear.new(
chainring:
52,
cog:
11,
wheel:
Wheel.new(26,
1.5))
assert_in_delta(137.1,
gear.gear_inches,
0.01)
gear.wheel.expect(:diameter)
gear.verify
end
end
Over Speci ed:
Adds costs but not bene ts
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@sandimetz Apr 2013
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Rule
Do not test
outgoing query messages
Saturday, April 27, 13
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@sandimetz Apr 2013
Rule
Do not test
outgoing query messages
Do not make assertions about their result
Saturday, April 27, 13
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@sandimetz Apr 2013
Rule
Do not test
outgoing query messages
Do not make assertions about their result
Do not expect to send them
Saturday, April 27, 13
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@sandimetz Apr 2013
If a message has
no visible side-effects
Saturday, April 27, 13
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@sandimetz Apr 2013
If a message has
no visible side-effects
the sender
should not test it
Saturday, April 27, 13
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Query Command
Assert
result
Assert
direct public
side effects
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Ignore
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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Query Command
Assert
result
Assert
direct public
side effects
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Ignore
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Outgoing
Command Messages
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
diameter
gear_inches
set_cog
changed
Wheel
Gear
Obs
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
Change #set_cog to add observer
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
attr_reader
:chainring,
:cog,
:wheel
def
initialize(args)
#
...
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
attr_reader
:chainring,
:cog,
:wheel,
:observer
def
initialize(args)
#
...
@observer
=
args[:observer]
end
def
set_cog(new_cog)
@cog
=
new_cog
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
changed
@cog
end
def
changed
observer.changed(chainring,
cog)
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
changed
@cog
end
def
changed
observer.changed(chainring,
cog)
end
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
set_cog
changed
Obs
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
set_cog
changed
Obs
Side
Effects
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
changed
Gear
set_cog
Obs
Incoming
Command
Side
Effects
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Gear
Outgoing
set_cog
Obs
changed
Incoming
Command
Side
Effects
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
changed
@cog
end
def
changed
observer.changed(chainring,
cog)
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
Gear
#
...
def
set_cog(new_cog)
@cog
=
new_cog
changed
@cog
end
def
changed
observer.changed(chainring,
cog)
end
end
This message MUST get sent
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self Outgoing
Incoming
Anti-Pattern
to Self
Incoming Outgoing
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Depends on the distant side effect
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Is this Gear’s responsibility?
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
Is this Gear’s responsibility?
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_saves_changed_cog_in_db
@observer
=
Obs.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@gear.set_cog(27)
#
assert
something
about
the
state
of
the
db
end
end
This is an integration test
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Depends on the interface
Saturday, April 27, 13
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@sandimetz GoGaRuCo 2012
@sandimetz Apr 2013
to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
Gear is responsible for sending
#changed to @observer
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@sandimetz Apr 2013
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Expect to send
outgoing command messages
Rule
Saturday, April 27, 13
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@sandimetz Apr 2013
Break rule if side effects
are stable and cheap
Caveat
Saturday, April 27, 13
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Slide 175 text
Query Command
Assert
result
Assert
direct public
side effects
Ignore
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Ignore
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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Slide 176 text
Query Command
Assert
result
Assert
direct public
side effects
Ignore Expect
to send
The Unit Testing Minimalist
Incoming
Type
@sandimetz Apr 2013
Message
Ignore
Sent to Self
Outgoing
Origin
Saturday, April 27, 13
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@sandimetz Apr 2013
But
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@sandimetz GoGaRuCo 2012
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to Self
Incoming Outgoing
class
GearTest
<
MiniTest::Unit::TestCase
def
test_notifies_observers_when_cogs_change
@observer
=
MiniTest::Mock.new
@gear
=
Gear.new(
chainring:
52,
cog:
11,
observer:
@observer)
@observer.expect(:changed,
true,
[52,
27])
@gear.set_cog(27)
@observer.verify
end
What happens if Observer
stops implementing #changed?
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Pain
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API Drift
Pain
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Rule
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Honor the contract
Rule
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Honor the contract
Ensure test doubles stay in sync with the API
Rule
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Automagically
minitest: requires that stubbed methods exist
rspec: #should_receive(:msg).and_call_original
https://github.com/psyho/bogus
https://github.com/benmoss/quacky
https://github.com/xaviershay/rspec-‐fire
https://github.com/cfcosta/minitest-‐firemock
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Summary
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Be a
minimalist
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Query Command
Assert
result
Assert
direct public
side effects
Ignore Expect
to send
Incoming
Type
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Message
Ignore
Sent to Self
Outgoing
Origin
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Use good
judgement
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Test
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Test.
Everything
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@sandimetz Apr 2013
Test
.
Everything.
Once
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Test the
interface
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Trust
collaborators
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Insist on
simplicity
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Practice the Tricks
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I love my tests
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Thanks
Sandi Metz
@sandimetz
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http://www. ickr.com/photos/phil_shirley/5452562957/ thicket
http://www. ickr.com/photos/zebble/6080622/ one padlock
http://www. ickr.com/photos/chrisinplymouth/5543281168/ two padlocks
http://www. ickr.com/photos/donjohnson395/2915304926/ twins at beach
http://www.med.navy.mil/sites/nmcp/Patients/pediatrics/PublishingImages/binocular_boy.gif
http://upload.wikimedia.org/wikipedia/commons/e/e1/Ordinary_bicycle02.jpg ordinary bike
Magic Hat (82805980) Copyright Mmaxer - Shutterstock.com
Dogs in Hats (39263399) Copyright MLoiselle - Fotolia.com
Garden (35521385) Copyright Beboy - Fotolia.com
Space Walk - Nasa http://grin.hq.nasa.gov/copyright.html
Photo Credits
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http://poodr.info
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Questions?
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http://poodr.info
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