test(DropDownAlert): add unit test

[trunghieuvn]

Hi @vantuan88291 thank for your package.

please review unit test here and fix some issue can't render because timer not init

@override
  void dispose() {
    super.dispose();
    _controller?.dispose();
    _controller = null;
    _timer!.cancel();
    _timerRelay!.cancel();
  }

[trunghieuvn]

log error if not workaround

AlertController was created!
══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following _CastError was thrown while finalizing the widget tree:
Null check operator used on a null value

When the exception was thrown, this was the stack:
#0      DropdownAlertWidget.dispose (package:flutter_dropdown_alert/dropdown_alert.dart:228:11)
#1      StatefulElement.unmount (package:flutter/src/widgets/framework.dart:4800:11)
#2      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1847:13)
#3      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#4      MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:6185:16)
#5      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#6      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#7      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#8      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#9      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#10     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#11     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#12     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#13     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#14     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#15     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#16     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#17     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#18     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#19     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#20     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#21     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#22     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#23     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#24     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#25     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#26     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#27     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#28     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#29     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#30     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#31     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#32     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#33     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#34     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#35     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#36     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#37     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#38     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#39     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#40     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#41     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#42     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#43     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:6070:14)
#44     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#45     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#46     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#47     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#48     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#49     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#50     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#51     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#52     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#53     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#54     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#55     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#56     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#57     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#58     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#59     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#60     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#61     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:6070:14)
#62     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#63     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#64     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#65     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#66     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#67     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#68     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#69     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#70     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#71     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#72     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#73     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#74     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#75     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#76     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#77     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#78     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#79     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#80     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#81     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#82     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#83     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#84     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#85     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#86     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#87     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#88     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#89     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#90     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#91     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#92     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#93     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#94     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#95     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#96     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#97     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#98     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#99     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#100    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:6070:14)
#101    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#102    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#103    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#104    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#105    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#106    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#107    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#108    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#109    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#110    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#111    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#112    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#113    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#114    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#115    SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:6070:14)
#116    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#117    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#118    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#119    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#120    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#121    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#122    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#123    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#124    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#125    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#126    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#127    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#128    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#129    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#130    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#131    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#132    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#133    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#134    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#135    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#136    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#137    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#138    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#139    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#140    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#141    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#142    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#143    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#144    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#145    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#146    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#147    _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1845:7)
#148    ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4628:14)
#149    _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1843:13)
#150    ListIterable.forEach (dart:_internal/iterable.dart:39:13)
#151    _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1856:25)
#152    BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2840:27)
#153    BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2473:15)
#154    BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2839:7)
#155    AutomatedTestWidgetsFlutterBinding.drawFrame (package:flutter_test/src/binding.dart:1126:19)
#156    RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:328:5)
#157    SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1144:15)
#158    SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1082:9)
#159    AutomatedTestWidgetsFlutterBinding.scheduleWarmUpFrame (package:flutter_test/src/binding.dart:1052:5)
#160    runApp (package:flutter/src/widgets/binding.dart:1029:7)
#161    TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:800:7)
<asynchronous suspension>
════════════════════════════════════════════════════════════════════════════════════════════════════
00:02 +0 -1: description WHEN open screen LoginScreen, THEN should render basic successfully [E]                                                                                                                               
  Test failed. See exception logs above.
  The test description was: WHEN open screen LoginScreen, THEN should render basic successfully
  
00:02 +0 -1: Some tests failed.                                                                                                                                                                                                
TrungHieu:flutter_dropdown_alert macbookpro$