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@sandimetz May 2013 The Magic Tricks of Testing Sandi Metz Saturday, May 25, 2013

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@sandimetz May 2013 Why do I hate my tests? Saturday, May 25, 2013

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@sandimetz May 2013 Why do I hate my tests? Saturday, May 25, 2013

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@sandimetz May 2013 They’re slow Saturday, May 25, 2013

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@sandimetz May 2013 They’re fragile Saturday, May 25, 2013

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@sandimetz May 2013 They’re expensive Saturday, May 25, 2013

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@sandimetz May 2013 They are misery Saturday, May 25, 2013

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@sandimetz May 2013 They are misery incarnate Saturday, May 25, 2013

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@sandimetz May 2013 It doesn’t have to be this way Saturday, May 25, 2013

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@sandimetz May 2013 Just delete some tests Saturday, May 25, 2013

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@sandimetz May 2013 Unit Tests: Goals Saturday, May 25, 2013

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@sandimetz May 2013 Thorough Unit Tests: Goals Saturday, May 25, 2013

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@sandimetz May 2013 Thorough Stable Unit Tests: Goals Saturday, May 25, 2013

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@sandimetz May 2013 Thorough Stable Fast Unit Tests: Goals Saturday, May 25, 2013

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@sandimetz May 2013 Thorough Stable Fast Few Unit Tests: Goals Saturday, May 25, 2013

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@sandimetz May 2013 How does your app feel? Saturday, May 25, 2013

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@sandimetz May 2013 Saturday, May 25, 2013

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@sandimetz May 2013 Focus on messages Saturday, May 25, 2013

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@sandimetz May 2013 Objects are simple-minded Saturday, May 25, 2013

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@sandimetz May 2013 Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Saturday, May 25, 2013

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@sandimetz May 2013 Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Object Under Test Received from others Saturday, May 25, 2013

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@sandimetz May 2013 Object Under Test Received from others Saturday, May 25, 2013

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@sandimetz May 2013 Object Under Test Incoming Saturday, May 25, 2013

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@sandimetz May 2013 Sent to others Incoming Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to others Incoming Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Incoming Sent to Self Outgoing Message Origin Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Sent to self Incoming Outgoing Query Command Object Under Test Saturday, May 25, 2013

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@sandimetz May 2013 Query Command Message Type Saturday, May 25, 2013

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@sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013

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@sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013

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@sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013

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@sandimetz May 2013 We conflate commands and queries at our peril Saturday, May 25, 2013

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@sandimetz May 2013 but we do it all the time Saturday, May 25, 2013

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Query Command Message Origin x Type Outgoing Incoming Type Origin @sandimetz May 2013 Message Sent to Self Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 1 Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Query Messages Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Wheel diameter Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Test incoming query messages Rule Saturday, May 25, 2013

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@sandimetz May 2013 Test incoming query messages by making assertions about what they send back Rule Saturday, May 25, 2013

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Query Command The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013

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Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Another Incoming Query Message Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear gear_inches Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Sight along the edges of the space capsule Saturday, May 25, 2013

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@sandimetz May 2013 Sight along the edges of the space capsule Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz May 2013 Test the interface Saturday, May 25, 2013

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@sandimetz May 2013 Test the interface (not the implementation) Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Command Messages Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Test incoming command messages Rule Saturday, May 25, 2013

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@sandimetz May 2013 Test incoming command messages by making assertions about direct public side effects Rule Saturday, May 25, 2013

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Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013

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Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Assert direct public side effects Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz May 2013 DRY It Out Saturday, May 25, 2013

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@sandimetz May 2013 Receiver of incoming message has sole responsibility DRY It Out Saturday, May 25, 2013

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@sandimetz May 2013 Receiver of incoming message has sole responsibility for asserting the result direct public side effects DRY It Out Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 2 to Self Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Messages Sent to Self to Self Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Do not test private methods Rule Saturday, May 25, 2013

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@sandimetz May 2013 Do not test private methods Do not make assertions about their result Rule Saturday, May 25, 2013

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@sandimetz May 2013 Do not test private methods Do not make assertions about their result Do not expect to send them Rule Saturday, May 25, 2013

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@sandimetz May 2013 Break rule if it saves $$$ during development Caveat Saturday, May 25, 2013

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Query Command Assert result Assert direct public side-effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013

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Query Command Assert result Assert direct public side-effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Ignore Message Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 3 to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Outgoing Query Messages to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Spoiler Alert Same rules as ‘Sent to Self’ to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming diameter Gear gear_inches Wheel to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear Gear Outgoing Wheel diameter Incoming Query gear_inches to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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? Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Rule Do not test outgoing query messages Saturday, May 25, 2013

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@sandimetz May 2013 Rule Do not test outgoing query messages Do not make assertions about their result Saturday, May 25, 2013

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@sandimetz May 2013 Rule Do not test outgoing query messages Do not make assertions about their result Do not expect to send them Saturday, May 25, 2013

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@sandimetz May 2013 If a message has no visible side-effects Saturday, May 25, 2013

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@sandimetz May 2013 If a message has no visible side-effects the sender should not test it Saturday, May 25, 2013

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Query Command Assert result Assert direct public side effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013

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Query Command Assert result Assert direct public side effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Outgoing Command Messages to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming diameter gear_inches set_cog changed Wheel Gear Obs to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Incoming Outgoing class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Incoming Outgoing class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog changed Obs to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog changed Obs Side Effects to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming changed Gear set_cog Obs Incoming Command Side Effects to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear Outgoing set_cog Obs changed Incoming Command Side Effects to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Outgoing Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Expect to send outgoing command messages Rule Saturday, May 25, 2013

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@sandimetz May 2013 Break rule if side effects are stable and cheap Caveat Saturday, May 25, 2013

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Query Command Assert result Assert direct public side effects Ignore The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013

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Query Command Assert result Assert direct public side effects Ignore Expect to send The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz May 2013 But Saturday, May 25, 2013

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@sandimetz GoGaRuCo 2012 @sandimetz May 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 What happens if Observer stops implementing #changed? Saturday, May 25, 2013

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@sandimetz May 2013 Pain Saturday, May 25, 2013

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@sandimetz May 2013 API Drift Pain Saturday, May 25, 2013

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@sandimetz May 2013 Rule Saturday, May 25, 2013

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@sandimetz May 2013 Honor the contract Rule Saturday, May 25, 2013

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@sandimetz May 2013 Honor the contract Ensure test doubles stay in sync with the API Rule Saturday, May 25, 2013

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@sandimetz May 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, May 25, 2013

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@sandimetz May 2013 Summary Saturday, May 25, 2013

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@sandimetz May 2013 Be a minimalist Saturday, May 25, 2013

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Query Command Assert result Assert direct public side effects Ignore Expect to send Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013

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@sandimetz May 2013 Use good judgement Saturday, May 25, 2013

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@sandimetz May 2013 Test Saturday, May 25, 2013

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@sandimetz May 2013 Test. Everything Saturday, May 25, 2013

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@sandimetz May 2013 Test . Everything. Once Saturday, May 25, 2013

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@sandimetz May 2013 Test the interface Saturday, May 25, 2013

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@sandimetz May 2013 Trust collaborators Saturday, May 25, 2013

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@sandimetz May 2013 Insist on simplicity Saturday, May 25, 2013

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@sandimetz May 2013 Practice the Tricks Saturday, May 25, 2013

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@sandimetz May 2013 Saturday, May 25, 2013

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@sandimetz May 2013 Saturday, May 25, 2013

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@sandimetz May 2013 I love my tests Saturday, May 25, 2013

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Thanks Sandi Metz @sandimetz Saturday, May 25, 2013

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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 Saturday, May 25, 2013

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@sandimetz May 2013 http://poodr.info Saturday, May 25, 2013

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Questions? Saturday, May 25, 2013

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@sandimetz May 2013 http://poodr.info Saturday, May 25, 2013