title: How to use get_it (flutter dependency injection) in the widget test?
body: <p>When I use dependency injections in a project, my widget tests fails.</p>
  <p>My error is as follows:</p>
  <pre><code>Testing started at 10:07 AM ...
  C:\src\flutter\bin\flutter.bat --no-color test --machine --plain-name &quot;Exist FloatingActionButton&quot; test\features\announcement\presentation\widgets_test\announcement_widget_test.dart
  ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞══════════════════════'═════════════════════════════════════
  The following assertion was thrown building _BodyBuilder:
  No type AnnouncementBloc is registered inside GetIt.
  Did you forget to pass an instance name?
  (Did you accidentally do GetIt sl=GetIt.instance(); instead of GetIt sl=GetIt.instance;did you
  forget to register it?)
  'package:get_it/get_it_impl.dart':
  Failed assertion: line 251 pos 14: 'instanceFactory != null'
  
  The relevant error-causing widget was:
  Scaffold
  file:///C:/Projects/niaz-flutter/lib/features/announcement/presentation/pages/announcements_page.dart:15:12
  
  When the exception was thrown, this was the stack:
  #2 _GetItImplementation._findFactoryByNameOrType (package:get_it/get_it_impl.dart:251:14)
  #3 _GetItImplementation.get (package:get_it/get_it_impl.dart:263:27)
  #4 _GetItImplementation.call (package:get_it/get_it_impl.dart:288:12)
  #5 new _AnnouncementsWidgetState (package:niaz/features/announcement/presentation/widgets/announcements_widget.dart:22:19)
  #6 AnnouncementsWidget.createState (package:niaz/features/announcement/presentation/widgets/announcements_widget.dart:18:46)
  #7 new StatefulElement (package:flutter/src/widgets/framework.dart:4600:25)
  #8 StatefulWidget.createElement (package:flutter/src/widgets/framework.dart:896:38)
  ... Normal element mounting (19 frames)
  #27 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3455:14)
  #28 MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5956:32)
  ... Normal element mounting (193 frames)
  #221 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3455:14)
  #222 MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5956:32)
  ... Normal element mounting (255 frames)
  #477 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3455:14)
  #478 Element.updateChild (package:flutter/src/widgets/framework.dart:3220:20)
  #479 RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1132:16)
  #480 RenderObjectToWidgetElement.update (package:flutter/src/widgets/binding.dart:1110:5)
  #481 RenderObjectToWidgetElement.performRebuild (package:flutter/src/widgets/binding.dart:1124:7)
  #482 Element.rebuild (package:flutter/src/widgets/framework.dart:4227:5)
  #483 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2632:33)
  #484 AutomatedTestWidgetsFlutterBinding.drawFrame (package:flutter_test/src/binding.dart:1016:18)
  #485 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:284:5)
  #486 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1113:15)
  #487 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1052:9)
  #488 AutomatedTestWidgetsFlutterBinding.pump. (package:flutter_test/src/binding.dart:889:9)
  #491 TestAsyncUtils.guard (package:flutter_test/src/test_async_utils.dart:72:41)
  #492 AutomatedTestWidgetsFlutterBinding.pump (package:flutter_test/src/binding.dart:876:27)
  #493 WidgetTester.pumpWidget. (package:flutter_test/src/widget_tester.dart:462:22)
  #496 TestAsyncUtils.guard (package:flutter_test/src/test_async_utils.dart:72:41)
  #497 WidgetTester.pumpWidget (package:flutter_test/src/widget_tester.dart:459:27)
  #498 main. (file:///C:/Projects/niaz-flutter/test/features/announcement/presentation/widgets_test/announcement_widget_test.dart:15:18)
  #499 main. (file:///C:/Projects/niaz-flutter/test/features/announcement/presentation/widgets_test/announcement_widget_test.dart:14:45)
  #500 testWidgets.. (package:flutter_test/src/widget_tester.dart:144:29)
  #511 FakeAsync.flushMicrotasks (package:fake_async/fake_async.dart:192:32)
  #512 AutomatedTestWidgetsFlutterBinding.runTest. (package:flutter_test/src/binding.dart:1109:17)
  #513 AutomatedTestWidgetsFlutterBinding.runTest. (package:flutter_test/src/binding.dart:1097:35)
  (elided 31 frames from class _AssertionError, dart:async, and package:stack_trace)
  
  ════════════════════════════════════════════════════════════════════════════════════════════════════
  
  Test failed. See exception logs above.
  </code></pre>
  <p>The test description was: Exist FloatingActionButton</p>