Magic Tricks of Testing (RailsConf)

@sandimetz Apr 2013 The Magic Tricks of Testing Sandi Metz
Saturday, April 27, 13

@sandimetz Apr 2013 Why do I hate my tests? Saturday,
April 27, 13

@sandimetz Apr 2013 They’re slow Saturday, April 27, 13

@sandimetz Apr 2013 They’re fragile Saturday, April 27, 13

@sandimetz Apr 2013 They’re expensive Saturday, April 27, 13

@sandimetz Apr 2013 They are misery Saturday, April 27, 13

@sandimetz Apr 2013 They are misery incarnate Saturday, April 27,
13

@sandimetz Apr 2013 It doesn’t have to be this way

@sandimetz Apr 2013 Just delete some tests Saturday, April 27,
13

@sandimetz Apr 2013 Unit Tests: Goals Saturday, April 27, 13

@sandimetz Apr 2013 Thorough Unit Tests: Goals Saturday, April 27,
13

@sandimetz Apr 2013 Thorough Stable Unit Tests: Goals Saturday, April
27, 13

@sandimetz Apr 2013 Thorough Stable Fast Unit Tests: Goals Saturday,
April 27, 13

@sandimetz Apr 2013 Thorough Stable Fast Few Unit Tests: Goals

@sandimetz Apr 2013 How does your app feel? Saturday, April
27, 13

@sandimetz Apr 2013 Saturday, April 27, 13

@sandimetz Apr 2013 Focus on messages Saturday, April 27, 13

@sandimetz Apr 2013 Objects are simple-minded Saturday, April 27, 13

@sandimetz Apr 2013 Object Under Test Saturday, April 27, 13

@sandimetz Apr 2013 Object Under Test Received from others Saturday,
April 27, 13

@sandimetz Apr 2013 Object Under Test Incoming Saturday, April 27,
13

@sandimetz Apr 2013 Sent to others Incoming Object Under Test

@sandimetz Apr 2013 Incoming Outgoing Object Under Test Saturday, April
27, 13

@sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under
Test Saturday, April 27, 13

@sandimetz Apr 2013 Incoming Sent to Self Outgoing Message Origin

@sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under
Test Saturday, April 27, 13

@sandimetz Apr 2013 Sent to self Incoming Outgoing Query Command
Object Under Test Saturday, April 27, 13

@sandimetz Apr 2013 Query Command Message Type Saturday, April 27,
13

@sandimetz Apr 2013 Query: Return something/ change nothing Command: Return
nothing/ change something Type Saturday, April 27, 13

@sandimetz Apr 2013 We conflate commands and queries at our
peril Saturday, April 27, 13

@sandimetz Apr 2013 but we do it all the time

Query Command Message Origin x Type Outgoing Incoming Type Origin
@sandimetz Apr 2013 Message Sent to Self Saturday, April 27, 13

@sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming
Part 1 Incoming Saturday, April 27, 13

Incoming Query Messages Incoming Saturday, April 27, 13

Incoming Wheel diameter Saturday, April 27, 13

class Wheel attr_reader :rim, :tire def initialize(rim, tire) # ... end def diameter rim + (tire * 2) end # ... Saturday, April 27, 13

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 Saturday, April 27, 13

@sandimetz Apr 2013 Rule Saturday, April 27, 13

@sandimetz Apr 2013 Test incoming query messages Rule Saturday, April
27, 13

@sandimetz Apr 2013 Test incoming query messages by making assertions
about what they send back Rule Saturday, April 27, 13

Query Command The Unit Testing Minimalist Incoming Type @sandimetz Apr
2013 Message Sent to Self Outgoing Origin Saturday, April 27, 13

Query Command Assert result The Unit Testing Minimalist Incoming Type
@sandimetz Apr 2013 Message Sent to Self Outgoing Origin Saturday, April 27, 13

Incoming Another Incoming Query Message Saturday, April 27, 13

Gear gear_inches Incoming Saturday, April 27, 13

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

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 Saturday, April 27, 13

@sandimetz Apr 2013 Sight along the edges of the space
capsule Saturday, April 27, 13

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

@sandimetz Apr 2013 Test the interface Saturday, April 27, 13

@sandimetz Apr 2013 Test the interface (not the implementation) Saturday,
April 27, 13

Incoming Command Messages Incoming Saturday, April 27, 13

Gear set_cog Incoming Saturday, April 27, 13

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

class GearTest < MiniTest::Unit::TestCase def test_set_cog gear = Gear.new gear.set_cog(27) assert(27, gear.cog) end end Saturday, April 27, 13

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 Saturday, April 27, 13

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 Saturday, April 27, 13

@sandimetz Apr 2013 Test incoming command messages Rule Saturday, April
27, 13

@sandimetz Apr 2013 Test incoming command messages by making assertions
about direct public side eﬀects Rule Saturday, April 27, 13

@sandimetz Apr 2013 Message Sent to Self Outgoing Origin Saturday, April 27, 13

@sandimetz Apr 2013 Message Assert direct public side eﬀects Sent to Self Outgoing Origin Saturday, April 27, 13

@sandimetz Apr 2013 DRY It Out Saturday, April 27, 13

@sandimetz Apr 2013 Receiver of incoming message has sole responsibility
DRY It Out Saturday, April 27, 13

@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

Part 2 to Self Incoming Saturday, April 27, 13

Messages Sent to Self to Self Incoming Saturday, April 27, 13

class Gear # ... def gear_inches ratio * wheel.diameter end private def ratio chainring / cog.to_f end # ... end Saturday, April 27, 13

Anti-Pattern to Self Incoming Saturday, April 27, 13

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

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

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

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

Anti-Pattern to Self Incoming Saturday, April 27, 13

class Gear # ... def gear_inches ratio * wheel.diameter end private def ratio chainring / cog.to_f end # ... end Saturday, April 27, 13

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

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

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 Saturday, April 27, 13

@sandimetz Apr 2013 Do not test private methods Rule Saturday,
April 27, 13

@sandimetz Apr 2013 Do not test private methods Do not
make assertions about their result Rule Saturday, April 27, 13

@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

@sandimetz Apr 2013 Break rule if it saves $$$ during
development Caveat Saturday, April 27, 13

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

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

Part 3 to Self Incoming Outgoing Saturday, April 27, 13

Outgoing Query Messages to Self Incoming Outgoing Saturday, April 27, 13

Spoiler Alert Same rules as ‘Sent to Self’ to Self Incoming Outgoing Saturday, April 27, 13

diameter Gear gear_inches Wheel to Self Incoming Outgoing Saturday, April 27, 13

@sandimetz GoGaRuCo 2012 @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 Saturday, April 27, 13

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 Saturday, April 27, 13

Gear Gear Outgoing Wheel diameter Incoming Query gear_inches to Self Incoming Outgoing Saturday, April 27, 13

Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, April 27, 13

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 Saturday, April 27, 13

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

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

Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, April 27, 13

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 Saturday, April 27, 13

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? Saturday, April 27, 13

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 Saturday, April 27, 13

@sandimetz Apr 2013 Rule Do not test outgoing query messages

Do not make assertions about their result Saturday, April 27, 13

Do not make assertions about their result Do not expect to send them Saturday, April 27, 13

@sandimetz Apr 2013 If a message has no visible side-eﬀects

@sandimetz Apr 2013 If a message has no visible side-eﬀects
the sender should not test it Saturday, April 27, 13

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

Outgoing Command Messages to Self Incoming Outgoing Saturday, April 27, 13

diameter gear_inches set_cog changed Wheel Gear Obs to Self Incoming Outgoing Saturday, April 27, 13

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 Saturday, April 27, 13

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

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 Saturday, April 27, 13

class Gear # ... def set_cog(new_cog) @cog = new_cog end end Saturday, April 27, 13

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

Gear set_cog changed Obs to Self Incoming Outgoing Saturday, April 27, 13

Gear set_cog changed Obs Side Effects to Self Incoming Outgoing Saturday, April 27, 13

changed Gear set_cog Obs Incoming Command Side Effects to Self Incoming Outgoing Saturday, April 27, 13

Gear Outgoing set_cog Obs changed Incoming Command Side Effects to Self Incoming Outgoing Saturday, April 27, 13

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

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 Saturday, April 27, 13

Anti-Pattern to Self Incoming Outgoing Saturday, April 27, 13

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

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 Saturday, April 27, 13

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

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

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

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

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 Saturday, April 27, 13

@sandimetz Apr 2013 Expect to send outgoing command messages Rule

@sandimetz Apr 2013 Break rule if side eﬀects are stable
and cheap Caveat Saturday, April 27, 13

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

Expect to send The Unit Testing Minimalist Incoming Type @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Origin Saturday, April 27, 13

@sandimetz Apr 2013 But Saturday, April 27, 13

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? Saturday, April 27, 13

@sandimetz Apr 2013 Pain Saturday, April 27, 13

@sandimetz Apr 2013 API Drift Pain Saturday, April 27, 13

@sandimetz Apr 2013 Honor the contract Rule Saturday, April 27,
13

@sandimetz Apr 2013 Honor the contract Ensure test doubles stay
in sync with the API Rule Saturday, April 27, 13

@sandimetz Apr 2013 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 Saturday, April 27, 13

@sandimetz Apr 2013 Summary Saturday, April 27, 13

@sandimetz Apr 2013 Be a minimalist Saturday, April 27, 13

Expect to send Incoming Type @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Origin Saturday, April 27, 13

@sandimetz Apr 2013 Use good judgement Saturday, April 27, 13

@sandimetz Apr 2013 Test Saturday, April 27, 13

@sandimetz Apr 2013 Test. Everything Saturday, April 27, 13

@sandimetz Apr 2013 Test . Everything. Once Saturday, April 27,
13

@sandimetz Apr 2013 Test the interface Saturday, April 27, 13

@sandimetz Apr 2013 Trust collaborators Saturday, April 27, 13

@sandimetz Apr 2013 Insist on simplicity Saturday, April 27, 13

@sandimetz Apr 2013 Practice the Tricks Saturday, April 27, 13

@sandimetz Apr 2013 I love my tests Saturday, April 27,
13

Thanks Sandi Metz @sandimetz Saturday, April 27, 13

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 Saturday, April 27, 13

@sandimetz Apr 2013 http://poodr.info Saturday, April 27, 13

Questions? Saturday, April 27, 13

@sandimetz Apr 2013 http://poodr.info Saturday, April 27, 13

Magic Tricks of Testing (RailsConf)

Magic Tricks of Testing (RailsConf)

More Decks by Sandi Metz

Other Decks in Programming

Featured

Transcript