君はPower Assertを知っているか #potatotips

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܅͸ Power Assert Λ஌͍ͬͯΔ͔ FUJI Goro (@__gfx__), a software engineer in COOKPAD #potatotips 2014/5/15 at DeNA

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FUJI Goro (@__gfx__) • software engineer @ COOKPAD Inc. • Android / iOS ޲͚ڞ௨ϥΠϒϥϦͷઃܭɾ։ൃ

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Assertions in Java // EXPR͕ࣦഊ͢Δͱ throw new AssertionError() Λ࣮ߦ͢Δ assert foo == 42; ! // comment͸AssertionErrorͷҾ਺ͱͯ͠౉͞ΕΔ assert foo == 42 : “with message”; ! // assertແޮ࣌͸͕ࣜධՁ͞Εͳ͍ͷͰॏΊͷલఏ৚݅νΣοΫ΋Մ assert checkParamsButSlow(foo);

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Assertions in Android • AndroidͰ͸Javaͷassertจ͕࢖͑Δ • `assert getActivity() != null;` • ͨͩ͠assert͸σϑΥϧτͰແޮ • `adb shell setprop debug.assert 1` Ͱ༗ޮԽ • …Ͱ͖Δ͜ͱ΋͋Δʢ࣮ػͩͱͰ͖ͳ͍ʁʣ

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Assertionsͷ໰୊఺ • εΠον͕ΞϓϦ͝ͱͰ͸ͳ͘୺຤͝ͱ • ͦ΋ͦ΋ޮ͔ͳ͔ͬͨΓ͢Δ͠ • ։ൃऀશһͰৗʹ༗ޮʹ͢Δͱ͍͏ͷ͸೉͍͠ • ࣦഊ࣌ͷ৘ใʹ๡͍͠ • ৄࡉΛ௥͏ͨΊʹϒϨʔΫϙΠϯτΛ࢓ࠐΜͰ σόοά͢Δඞཁ͕͋Δ

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ͭΒ͍

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ͱ͜ΖͰ Power Assert Λ஌͍ͬͯ·͔͢

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Power Assert ͷػೳ • assertࣦഊ࣌ʹؔ܎͢Δࣜͷ஋Λදࣔ͢Δ def x = new File(“foo.groovy”) assert x.absolutePath.contains("bar") // shows: Assertion failed: ! assert x.absolutePath.contains("bar") | | | | | false | /path/to/foo.groovy foo.groovy at foo.run(foo.groovy:4)

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࣮૷ͷͨΊͷπʔϧνΣΠϯ • ࣮ߦલʹίʔυΛॻ͖׵͑Δඞཁ͕͋Δ • JavaScript൛͸ιʔείʔυΛॻ͖׵͑Δ • Spock͸ίϯύΠϧޙͷASTΛॻ͖׵͑Δ • ASTʹରͯ͠ϝλϓϩάϥϛϯάͰ͖Δ؀ڥ ͕͋Ε͹OK

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AndroidͰ΋Power Assert͕ ࢖͍͍ͨੈքઢʹߦ͖͍ͨ…

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– OSSքͷ֨ݴ “ͩͬͨΒ͓લ͕΍Ε”

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΍Γ·ͨ͠

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Android Power Assert Plugin • assertจΛڧ੍తʹ༗ޮԽ • assertࣦഊ࣌ʹ৘ใΛ௥Ճ • ϦϦʔεϏϧυͰ͸Կ΋͠ͳ͍ • ࣮ߦ଎౓ʹӨڹ͸΄ͱΜͲͳ͠ • APKͷαΠζ΋૿͑ͳ͍

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ग़ྗྫ assert ﬁndViewById(R.id.never).isFocused();

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σϑΥϧτͷྫ֎

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assert ﬁndViewById(R.id.never).isFocused(); with default mode java.lang.NullPointerException: at MainActivity.onButton2Click(MainActivity.java:28) (…stacktrace͕ଓ͘…) ! // NOTE: // KitKat͔Β͸΋͏গ͠৘ใ͕૿͑ͯɺͳʹ͕nullͩͬͨͷ͔Θ͔Γ΍͘͢ͳ͍ͬͯΔ

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Power Assert༗ޮͷͱ͖

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assert ﬁndViewById(R.id.never).isFocused(); with power assert java.lang.NullPointerException: 26: void onButton2Click() { 27> assert findViewById(R.id.never).isFocused(); 27: } MainActivity.findViewById()= at MainActivity.onButton2Click(MainActivity.java:28) (…stacktrace͕ଓ͘…)

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࢖͍ํ // The root build.gradle buildscript { dependencies { classpath ‘com.github.gfx:android-power-assert-plugin:0.10.+’ } } ! // in build.gradle of a module apply plugin: ‘android-power-assert’

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͋ͱ͸assertจΛ࢖͏͚ͩ

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Power Assert ೋͭͷଆ໘

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ΞϓϦέʔγϣϯίʔυͰ࢖͏ • ؀ڥ͕ಛఆͷঢ়ଶͰ͋Δ͜ͱΛอূ͢Δ • Ҿ਺ͷνΣοΫ΍nullνΣοΫͳͲ • Android StudioͰNPEܯࠂΛ੩ΊΔͨΊ • ϦϦʔε൛Ͱassertจ͸ফ͑ΔͷͰɺ͋͘·Ͱ΋ ʮ։ൃऀ͕ਖ਼͍͠ίʔυΛॻ͍͍ͯΔ͜ͱΛอ ূ͢ΔʯͨΊʹ࢖͏

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ςετͰ࢖͏ • ൚༻ςετϚονϟʔͱͯ͠࢖͏ • JUnitͷassertEquals()ͷҾ਺ͷॱ൪Λߟ͑ͳ͘ ͯΑ͘ͳΔ • ࣜͷ్தܦաΛදࣔ͢ΔͷͰɺෳ਺ͷ assertXXX()Λ·ͱΊΒΕΔ • assert obj.foo().bar().equals(“baz”)

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How it works

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JavassistʹΑΔόΠτίʔυૢ࡞ • $assertionsDisabledΛৗʹfalseʹ͢Δ • assertจʢ͕ίϯύΠϧ͞ΕͨόΠτίʔυʣ Λݟ͚ͭͨΒपล৘ใΛूΊͯจࣈྻΛੜ੒ ͢ΔίʔυΛૠೖ͢Δ • ﬁeld access / method call͸try-catchͰғΜͰ NPEΛΩϟονˍपล৘ใΛ෇༩ͯ͠re-throw

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՝୊ • ෇Ճ৘ใ͕ଟ͗͢Δ • ͍·͸ϩʔΧϧม਺Λ͢΂ͯdump͍ͯ͠Δ • SpockͷΑ͏ͳࠩ෼දࣔΛ͍ͨ͠ • ͍·͸commonsͷToStringBuilderΛ࢖͍ͬͯΔ • JavassistͰେྔͷίʔυΛॻ͘ͷ͸ਏ͍ͷͰɺग़ྗ ϑΥʔϚολΛผʹ࣮૷͢Δඞཁ͕͋Δ

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We are hiring! https://info.cookpad.com/jobs/

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͝੩ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠ https://github.com/gfx/android-power-assert-plugin ਓபืूத