diff --git a/analysis_options.yaml b/analysis_options.yaml
index 51ab358a96..a41a74dafd 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -14,8 +14,21 @@ analyzer:
     - 'lib/src/third_party/pkg/**'
     - 'lib/templates/*.html'
     - 'pub.dartlang.org/**'
-    - 'testing/**'
+    # These have a lot of lint.
+    - 'testing/test_package/**'
+    - 'testing/test_package_custom_templates/**'
+    - 'testing/test_package_experiments/**'
+    - 'testing/test_package_export_error/**'
+    - 'testing/test_package_extensions/**'
+    - 'testing/test_package_import_export_error/**'
+    - 'testing/test_package_imported/**'
+    - 'testing/test_package_options/**'
+    # This package imports flutter, which is perhaps not found by the base `dart analyze` tool.
     - 'testing/flutter_packages/test_package_flutter_plugin/**'
+    # This package is meant to mock the sky_engine package.
+    - 'testing/sky_engine/**'
+    # These packages have compile-time errors.
+    - 'testing/test_package_bad/**'
     - 'testing/test_package_export_error/**'
 linter:
   rules:
diff --git a/analysis_options_presubmit.yaml b/analysis_options_presubmit.yaml
index 8b33a961ff..d8a57b0241 100644
--- a/analysis_options_presubmit.yaml
+++ b/analysis_options_presubmit.yaml
@@ -19,9 +19,21 @@ analyzer:
     - 'lib/src/third_party/pkg/**'
     - 'lib/templates/*.html'
     - 'pub.dartlang.org/**'
-    - 'testing/**'
-    - 'testing/flutter_packages/test_package_flutter_plugin/**'
+    # These have a lot of lint.
+    - 'testing/test_package/**'
+    - 'testing/test_package_custom_templates/**'
+    - 'testing/test_package_experiments/**'
     - 'testing/test_package_export_error/**'
+    - 'testing/test_package_extensions/**'
+    - 'testing/test_package_import_export_error/**'
+    - 'testing/test_package_imported/**'
+    - 'testing/test_package_options/**'
+    # This package imports flutter, which is perhaps not found by the base `dart analyze` tool.
+    - 'testing/flutter_packages/test_package_flutter_plugin/**'
+    # This package is meant to mock the sky_engine package.
+    - 'testing/sky_engine/**'
+    # These packages have compile-time errors.
+    - 'testing/test_package_bad/**'
 linter:
   rules:
     - always_declare_return_types
diff --git a/test/end2end/model_test.dart b/test/end2end/model_test.dart
index 8a41f48592..9f79076529 100644
--- a/test/end2end/model_test.dart
+++ b/test/end2end/model_test.dart
@@ -936,7 +936,9 @@ void main() {
     });
 
     test('does not have a null safety label if not null safe', () {
-      expect(exLibrary.isNullSafety, isFalse);
+      var optOutLibrary = packageGraph.libraries
+          .firstWhere((lib) => lib.name == 'opt_out_of_nnbd');
+      expect(optOutLibrary.isNullSafety, isFalse);
     });
 
     test('has a line number and column', () {
@@ -3381,7 +3383,7 @@ void main() {
       expect(
           thisIsFutureOrT.modelType.returnType.linkedName,
           equals(
-              'FutureOr<span class="signature">&lt;<wbr><span class="type-parameter">T</span>&gt;</span>'));
+              'FutureOr<span class="signature">&lt;<wbr><span class="type-parameter">T</span>&gt;</span>?'));
     });
 
     test('function with a parameter having type FutureOr<Null>', () {
@@ -3417,7 +3419,7 @@ void main() {
     test('has source code', () {
       expect(topLevelFunction.sourceCode, startsWith('@deprecated'));
       expect(topLevelFunction.sourceCode, endsWith('''
-String topLevelFunction(int param1, bool param2, Cool coolBeans,
+String? topLevelFunction(int param1, bool param2, Cool coolBeans,
     [double optionalPositional = 0.0]) {
   return null;
 }'''));
@@ -3486,15 +3488,19 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
     test('parameterized type from field is correctly displayed', () {
       var aField = TemplatedInterface.instanceFields
           .singleWhere((f) => f.name == 'aField');
-      expect(aField.modelType.linkedName,
-          '<a href="${htmlBasePlaceholder}ex/AnotherParameterizedClass-class.html">AnotherParameterizedClass</a><span class="signature">&lt;<wbr><span class="type-parameter">Stream<span class="signature">&lt;<wbr><span class="type-parameter">List<span class="signature">&lt;<wbr><span class="type-parameter">int</span>&gt;</span></span>&gt;</span></span>&gt;</span>');
+      expect(
+          aField.modelType.linkedName,
+          '<a href="${htmlBasePlaceholder}ex/AnotherParameterizedClass-class.html">AnotherParameterizedClass</a>'
+          '<span class="signature">&lt;<wbr><span class="type-parameter">Stream<span class="signature">&lt;<wbr><span class="type-parameter">List<span class="signature">&lt;<wbr><span class="type-parameter">int</span>&gt;</span></span>&gt;</span></span>&gt;</span>?');
     });
 
     test('parameterized type from inherited field is correctly displayed', () {
       var aInheritedField = TemplatedInterface.inheritedFields
           .singleWhere((f) => f.name == 'aInheritedField');
-      expect(aInheritedField.modelType.linkedName,
-          '<a href="${htmlBasePlaceholder}ex/AnotherParameterizedClass-class.html">AnotherParameterizedClass</a><span class="signature">&lt;<wbr><span class="type-parameter">List<span class="signature">&lt;<wbr><span class="type-parameter">int</span>&gt;</span></span>&gt;</span>');
+      expect(
+          aInheritedField.modelType.linkedName,
+          '<a href="${htmlBasePlaceholder}ex/AnotherParameterizedClass-class.html">AnotherParameterizedClass</a>'
+          '<span class="signature">&lt;<wbr><span class="type-parameter">List<span class="signature">&lt;<wbr><span class="type-parameter">int</span>&gt;</span></span>&gt;</span>?');
     });
 
     test(
@@ -3751,7 +3757,7 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
 
     test('method source code indents correctly', () {
       expect(convertToMap.sourceCode,
-          'Map&lt;X, Y&gt; convertToMap() =&gt; null;');
+          'Map&lt;X, Y&gt;? convertToMap() =&gt; null;');
     });
   });
 
@@ -4283,7 +4289,7 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
       expect(
           genericTypedefCombo.modelType.linkedName,
           equals(
-              '<a href="%%__HTMLBASE_dartdoc_internal__%%fake/NewGenericTypedef.html">NewGenericTypedef</a>'));
+              '<a href="%%__HTMLBASE_dartdoc_internal__%%fake/NewGenericTypedef.html">NewGenericTypedef</a>?'));
     });
 
     test('Verify that final and late show up (or not) appropriately', () {
@@ -4323,7 +4329,8 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
       expect(
           complicatedReturn.modelType.linkedName,
           equals(
-              '<a href="${htmlBasePlaceholder}fake/ATypeTakingClass-class.html">ATypeTakingClass</a><span class="signature">&lt;<wbr><span class="type-parameter">String Function<span class="signature">(<span class="parameter" id="param-"><span class="type-annotation">int</span></span>)</span></span>&gt;</span>'));
+              '<a href="${htmlBasePlaceholder}fake/ATypeTakingClass-class.html">ATypeTakingClass</a>'
+              '<span class="signature">&lt;<wbr><span class="type-parameter">String Function<span class="signature">(<span class="parameter" id="param-"><span class="type-annotation">int</span></span>)</span></span>&gt;</span>?'));
     });
 
     test('@nodoc on simple property works', () {
@@ -4878,7 +4885,7 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
 
     test('param with annotations', () {
       var method =
-          fakeLibrary.functions.firstWhere((f) => f.name == 'paintImage1');
+          fakeLibrary.functions.firstWhere((f) => f.name == 'paintImage2');
       var params =
           ParameterRendererHtml().renderLinkedParams(method.parameters);
       expect(
@@ -5104,16 +5111,18 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
     });
 
     test('Property fields are terminated with semicolon', () {
-      expect(finalProperty.sourceCode.trim(), endsWith('List&lt;int&gt;();'));
-      expect(simpleProperty.sourceCode.trim(), endsWith('List&lt;int&gt;();'));
+      expect(finalProperty.sourceCode.trim(),
+          endsWith('List&lt;int&gt;.filled(1, 1);'));
+      expect(simpleProperty.sourceCode.trim(),
+          endsWith('List&lt;int&gt;.filled(1, 1);'));
       expect(forInheriting.sourceCode.trim(), endsWith('forInheriting;'));
     });
 
     test('Arrow accessors are terminated with semicolon', () {
       expect(explicitGetterImplicitSetter.getter.sourceCode.trim(),
-          endsWith('List&lt;int&gt;();'));
+          endsWith('List&lt;int&gt;.filled(1, 1);'));
       expect(explicitGetterSetter.getter.sourceCode.trim(),
-          endsWith('List&lt;int&gt;();'));
+          endsWith('List&lt;int&gt;.filled(1, 1);'));
     });
 
     test('Traditional accessors are not terminated with semicolon', () {
@@ -5124,7 +5133,7 @@ String topLevelFunction(int param1, bool param2, Cool coolBeans,
 
     test('Whole declaration is visible when declaration spans many lines', () {
       expect(ensureWholeDeclarationIsVisible.sourceCode,
-          contains('List&lt;int&gt; '));
+          contains('List&lt;int&gt;? '));
     });
   });
 
diff --git a/testing/test_package/bin/drill.dart b/testing/test_package/bin/drill.dart
index a05daee47c..8217cbfa44 100644
--- a/testing/test_package/bin/drill.dart
+++ b/testing/test_package/bin/drill.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 // This is a sample "tool" used to test external tool integration into dartdoc.
 // It has no practical purpose other than that.
 
diff --git a/testing/test_package/bin/print_macro.dart b/testing/test_package/bin/print_macro.dart
index 4d5dd754f8..9b4cd5c9d1 100644
--- a/testing/test_package/bin/print_macro.dart
+++ b/testing/test_package/bin/print_macro.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 // This is a sample "tool" used to test external tool integration into dartdoc.
 // It has no other purpose.
 
diff --git a/testing/test_package/bin/setup.dart b/testing/test_package/bin/setup.dart
index d7e5619c21..a04713df33 100644
--- a/testing/test_package/bin/setup.dart
+++ b/testing/test_package/bin/setup.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 // This is a sample setup "tool" used to test external tool integration into
 // dartdoc. It has no practical purpose other than that.
 
diff --git a/testing/test_package/lib/anonymous_library.dart b/testing/test_package/lib/anonymous_library.dart
index 4312679443..bf450a8392 100644
--- a/testing/test_package/lib/anonymous_library.dart
+++ b/testing/test_package/lib/anonymous_library.dart
@@ -1,5 +1,3 @@
 // DO NOT give this library a name
 
-// @dart=2.9
-
 String doesStuff() => 'hi';
diff --git a/testing/test_package/lib/another_anonymous_lib.dart b/testing/test_package/lib/another_anonymous_lib.dart
index 94f1d0cbfc..9c52189194 100644
--- a/testing/test_package/lib/another_anonymous_lib.dart
+++ b/testing/test_package/lib/another_anonymous_lib.dart
@@ -1,5 +1,3 @@
 // DO NOT give this library a name
 
-// @dart=2.9
-
 String greeting() => "Hello";
diff --git a/testing/test_package/lib/base_class.dart b/testing/test_package/lib/base_class.dart
index 8913dd5b09..d35825e83e 100644
--- a/testing/test_package/lib/base_class.dart
+++ b/testing/test_package/lib/base_class.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library base_class;
 
 /// Abstract class Constraints
diff --git a/testing/test_package/lib/code_in_comments.dart b/testing/test_package/lib/code_in_comments.dart
index 4a6831af4a..f82cf1b34d 100644
--- a/testing/test_package/lib/code_in_comments.dart
+++ b/testing/test_package/lib/code_in_comments.dart
@@ -11,6 +11,4 @@
 ///   - 3.14
 /// ```
 
-// @dart=2.9
-
 library code_in_comments;
diff --git a/testing/test_package/lib/completely_empty_lib.dart b/testing/test_package/lib/completely_empty_lib.dart
index fdc4933219..8b13789179 100644
--- a/testing/test_package/lib/completely_empty_lib.dart
+++ b/testing/test_package/lib/completely_empty_lib.dart
@@ -1 +1 @@
-// @dart=2.9
+
diff --git a/testing/test_package/lib/css.dart b/testing/test_package/lib/css.dart
index 8aef383f2f..abe9048d39 100644
--- a/testing/test_package/lib/css.dart
+++ b/testing/test_package/lib/css.dart
@@ -2,8 +2,6 @@
 /// with directories created by dartdoc.
 /// {@category Other}
 
-// @dart=2.9
-
 library css;
 
 String theOnlyThingInTheLibrary = 'hello';
diff --git a/testing/test_package/lib/csspub.dart b/testing/test_package/lib/csspub.dart
index 0c142ff522..ce018e93a3 100644
--- a/testing/test_package/lib/csspub.dart
+++ b/testing/test_package/lib/csspub.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library csspub;
 
 String theOnlyThingInTheLibrary = 'hello';
diff --git a/testing/test_package/lib/example.dart b/testing/test_package/lib/example.dart
index 7d6a25afcd..fe205248cb 100644
--- a/testing/test_package/lib/example.dart
+++ b/testing/test_package/lib/example.dart
@@ -1,8 +1,6 @@
 /// a library. testing string escaping: `var s = 'a string'` <cool>
 /// {@category Real Libraries}
 
-// @dart=2.9
-
 library ex;
 
 import 'dart:async';
@@ -65,12 +63,12 @@ const List<String> PRETTY_COLORS = const <String>[
   'blue'
 ];
 @deprecated
-int deprecatedField;
+int deprecatedField = 1;
 
-double number;
+double number = 0.5;
 
 @deprecated
-int get deprecatedGetter => null;
+int? get deprecatedGetter => null;
 
 @deprecated
 void set deprecatedSetter(int value) {}
@@ -91,7 +89,7 @@ typedef String ParameterizedTypedef<T>(T msg, int foo);
 abstract class ParameterizedClass<T> {
   AnotherParameterizedClass<T> aInheritedMethod(int foo);
   ParameterizedTypedef<T> aInheritedTypedefReturningMethod();
-  AnotherParameterizedClass<T> aInheritedField;
+  AnotherParameterizedClass<T>? aInheritedField;
   AnotherParameterizedClass<T> get aInheritedGetter;
   ParameterizedClass<T> operator +(ParameterizedClass<T> other);
   set aInheritedSetter(AnotherParameterizedClass<T> thingToSet);
@@ -103,7 +101,7 @@ class AnotherParameterizedClass<B> {}
 abstract class TemplatedInterface<A> implements ParameterizedClass<List<int>> {
   AnotherParameterizedClass<List<int>> aMethodInterface(A value);
   ParameterizedTypedef<List<String>> aTypedefReturningMethodInterface();
-  AnotherParameterizedClass<Stream<List<int>>> aField;
+  AnotherParameterizedClass<Stream<List<int>>>? aField;
   AnotherParameterizedClass<Map<A, List<String>>> get aGetter;
   set aSetter(AnotherParameterizedClass<List<bool>> thingToSet);
 }
@@ -148,13 +146,13 @@ enum Animal {
 class Apple {
   static const int n = 5;
   static String string = 'hello';
-  String _s2;
+  String? _s2;
 
   /// The read-write field `m`.
   int m = 0;
 
   /// <nodoc> no docs
-  int notDocumented;
+  int? notDocumented;
 
   ///Constructor
   Apple();
@@ -171,12 +169,12 @@ class Apple {
   /**
    * The getter for `s`
    */
-  String get s => _s2;
+  String? get s => _s2;
 
   /**
    * The setter for `s`
    */
-  void set s(String something) {
+  void set s(String? something) {
     _s2 = something;
   }
 
@@ -200,7 +198,7 @@ class Apple {
 
   void paramFromExportLib(Helper helper) {}
 
-  void printMsg(String msg, [bool linebreak]) {}
+  void printMsg(String msg, [bool linebreak = false]) {}
 
   /**
    * fieldWithTypedef docs here
@@ -240,12 +238,12 @@ class B extends Apple with Cat {
    * The default value is `false` (compression disabled).
    * To enable, set `autoCompress` to `true`.
    */
-  bool autoCompress;
+  late bool autoCompress;
 
   /**
    * A list of Strings
    */
-  List<String> list;
+  List<String>? list;
 
   @override
   bool get isImplemented => false;
@@ -263,7 +261,7 @@ class B extends Apple with Cat {
     b * 2;
   }
 
-  void writeMsg(String msg, [String transformMsg(String origMsg, bool flag)]) {
+  void writeMsg(String msg, [String transformMsg(String origMsg, bool flag)?]) {
     // do nothing
   }
 
@@ -278,7 +276,7 @@ class RefsWithQsAndBangs {}
 class FieldAndCtorWithSameName {
   FieldAndCtorWithSameName.named();
 
-  int named;
+  int? named;
 }
 
 // Do NOT add a doc comment to C. Testing blank comments.
@@ -307,10 +305,10 @@ class ConstantCat implements Cat {
 
 /// implements [Cat], [E]
 class Dog implements Cat, E {
-  String name;
+  String? name;
 
   @deprecated
-  int deprecatedField;
+  int? deprecatedField;
 
   final int aFinalField = 42;
 
@@ -330,7 +328,7 @@ class Dog implements Cat, E {
   Dog.deprecatedCreate(this.name);
 
   @deprecated
-  int get deprecatedGetter => null;
+  int? get deprecatedGetter => null;
 
   @deprecated
   void set deprecatedSetter(int value) {}
@@ -343,7 +341,7 @@ class Dog implements Cat, E {
   @override
   operator ==(other) => other is Dog && name == other.name;
 
-  Dog operator +(Dog other) => Dog()..name = name + other.name;
+  Dog operator +(Dog other) => Dog()..name = name! + other.name!;
 
   foo() async => 42;
 
@@ -442,7 +440,7 @@ class Dog implements Cat, E {
 abstract class E {}
 
 class F<T extends String> extends Dog with _PrivateAbstractClass {
-  void methodWithGenericParam([List<Apple> msgs]) {}
+  void methodWithGenericParam([List<Apple>? msgs]) {}
 }
 
 class ForAnnotation {
@@ -471,7 +469,7 @@ class Klass {
 
   /// A shadowed method
   @override
-  toString() {}
+  toString() => '';
 
   /// A method with a custom annotation
   @aThingToDo('from', 'thing')
@@ -482,7 +480,7 @@ class MyError extends Error {}
 
 class MyErrorImplements implements Error {
   @override
-  StackTrace get stackTrace => null;
+  StackTrace? get stackTrace => null;
 }
 
 class MyException implements Exception {}
@@ -517,12 +515,12 @@ class SpecializedDuration extends Duration {}
  * class <nodoc>
  */
 class unDocumented {
-  String s;
+  String? s;
 }
 
 /// @nodoc
 class unDocumented2 {
-  String s;
+  String? s;
 }
 
 abstract class _PrivateAbstractClass {
@@ -615,7 +613,7 @@ extension AnExtension<Q> on WithGeneric<Q> {
 }
 
 class AnExtendableThing {
-  int aMember;
+  int? aMember;
 }
 
 extension SimpleStringExtension on AnExtendableThing {
@@ -638,7 +636,7 @@ extension FancyList<Z> on List<Z> {
   List<Z> operator -() => this.reversed.toList();
   List<List<Z>> split(int at) =>
       <List<Z>>[this.sublist(0, at), this.sublist(at)];
-  static List<Z> big() => List(1000000);
+  static List<Z?> big() => List.filled(100, null);
 }
 
 extension SymDiff<Q> on Set<Q> {
@@ -662,7 +660,7 @@ extension on Object {
 }
 
 extension StaticFieldExtension on Object {
-  static int aStatic;
+  static int? aStatic;
 }
 
 /// This class has nothing to do with [_Shhh], [FancyList], or [AnExtension.call],
@@ -675,12 +673,12 @@ class ToolPrintingMacroWhichInjectsHtml {
   /// {@template html-macro}
   /// {@inject-html}<div class="title">Title</div>{@end-inject-html}
   /// {@endtemplate}
-  int a;
+  int a = 1;
 
   /// Text.
   ///
   /// {@tool print_macro}
   /// Text for tool.
   /// {@end-tool}
-  int b;
+  int b = 2;
 }
diff --git a/testing/test_package/lib/excluded.dart b/testing/test_package/lib/excluded.dart
index 66d5cbd782..c04bd7cc6c 100644
--- a/testing/test_package/lib/excluded.dart
+++ b/testing/test_package/lib/excluded.dart
@@ -2,8 +2,6 @@
 /// even though it is located in the lib folder by
 /// using the <nodoc> tag
 
-// @dart=2.9
-
 library excluded;
 
 export 'example.dart' show Apple;
diff --git a/testing/test_package/lib/fake.dart b/testing/test_package/lib/fake.dart
index 02a7a3f956..c8124285e1 100644
--- a/testing/test_package/lib/fake.dart
+++ b/testing/test_package/lib/fake.dart
@@ -45,8 +45,6 @@
 ///
 /// [pkg]: http://example.org
 
-// @dart=2.9
-
 library fake;
 
 import 'dart:async';
@@ -88,7 +86,7 @@ abstract class ImplementingThingy implements BaseThingy {}
 abstract class BaseThingy {
   // ignore: public_member_api_docs
   ImplementingThingy get aImplementingThingy;
-  ImplementingThingy aImplementingThingyField;
+  ImplementingThingy? aImplementingThingyField;
   void aImplementingThingyMethod(ImplementingThingy parameter);
 }
 
@@ -123,14 +121,14 @@ class ConstructorTester<A, B> {
 class HasGenerics<X, Y, Z> {
   HasGenerics(X x, Y y, Z z) {}
 
-  X returnX() => null;
+  X? returnX() => null;
 
-  Z returnZ() => null;
+  Z? returnZ() => null;
 
-  Z doStuff(String s, X x) => null;
+  Z? doStuff(String s, X x) => null;
 
   /// Converts itself to a map.
-  Map<X, Y> convertToMap() => null;
+  Map<X, Y>? convertToMap() => null;
 }
 
 /// Coderef to ambiguous parameter of function parameter should not crash us.
@@ -138,8 +136,8 @@ class HasGenerics<X, Y, Z> {
 ///
 /// Here is a coderef: [aThingParameter]
 void doAComplicatedThing(int x,
-    {void doSomething(int aThingParameter, String anotherThing),
-    void doSomethingElse(int aThingParameter, double somethingElse)}) {}
+    {void doSomething(int aThingParameter, String anotherThing)?,
+    void doSomethingElse(int aThingParameter, double somethingElse)?}) {}
 
 /// Bullet point documentation.
 ///
@@ -202,8 +200,8 @@ dynamic get mustGetThis => null;
 
 Map<dynamic, String> mapWithDynamicKeys = {};
 
-Required useSomethingInAnotherPackage;
-String useSomethingInTheSdk;
+Required? useSomethingInAnotherPackage;
+String? useSomethingInTheSdk;
 
 /// Useful for annotations.
 class Annotation {
@@ -252,7 +250,7 @@ class AClassWithFancyProperties {
   ///   }
   /// }
   /// ```
-  String aProperty;
+  String? aProperty;
 }
 
 const _APrivateConstClass CUSTOM_CLASS_PRIVATE = const _APrivateConstClass();
@@ -302,10 +300,10 @@ typedef T GenericTypedef<T>(T input);
 typedef NewGenericTypedef<T> = List<S> Function<S>(T, int, bool);
 
 /// A top level variable with a generic typedef type.
-NewGenericTypedef genericTypedefCombo;
+NewGenericTypedef? genericTypedefCombo;
 
 /// A complicated type parameter to ATypeTakingClass.
-ATypeTakingClass<String Function(int)> get complicatedReturn => null;
+ATypeTakingClass<String Function(int)>? get complicatedReturn => null;
 
 /// Lots and lots of parameters.
 typedef int LotsAndLotsOfParameters(so, many, parameters, it, should, wrap,
@@ -313,7 +311,7 @@ typedef int LotsAndLotsOfParameters(so, many, parameters, it, should, wrap,
 
 /// This class is cool!
 class Cool {
-  // ignore: missing_return
+  // ignore: body_might_complete_normally
   Cool returnCool() {}
 }
 
@@ -361,71 +359,72 @@ class AClassUsingNewStyleMixin extends NotAMixin
 
 /// A generic class for testing type inference.
 class GenericClass<T> {
-  T member;
+  T? member;
 
   /// Destined to be overridden by [ModifierClass].
-  T overrideByModifierClass;
+  T? overrideByModifierClass;
 
   /// Destined to be overridden by [GenericMixin].
-  T overrideByGenericMixin;
+  T? overrideByGenericMixin;
 
   /// Destined to be overridden by [ModifierClass] and [GenericMixin], both.
-  T overrideByBoth;
+  T? overrideByBoth;
 
   /// Destined to be overridden by everything.
-  T overrideByEverything;
+  T? overrideByEverything;
 }
 
 /// A class extending a generic class.
 class ModifierClass<T> extends GenericClass<T> {
-  T modifierMember;
+  T? modifierMember;
 
   @override
-  T overrideByModifierClass;
+  T? overrideByModifierClass;
 
   @override
-  T overrideByBoth;
+  T? overrideByBoth;
 
   @override
-  T overrideByEverything;
+  T? overrideByEverything;
 }
 
 /// A generic mixin that requires GenericClass as a superclass.
 mixin GenericMixin<T> on GenericClass<T> {
-  T mixinMember;
+  T? mixinMember;
 
   @override
-  T overrideByGenericMixin;
+  T? overrideByGenericMixin;
 
   @override
-  T overrideByBoth;
+  T? overrideByBoth;
 
   @override
-  T overrideByEverything;
+  T? overrideByEverything;
 }
 
 /// A class verifying type inference across new-style mixins.
 class TypeInferenceMixedIn extends ModifierClass<int> with GenericMixin {
   @override
-  int overrideByEverything;
+  int? overrideByEverything;
 }
 
-GenericMixin<T> aMixinReturningFunction<T>() => null;
+GenericMixin<T>? aMixinReturningFunction<T>() => null;
 
 functionUsingMixinReturningFunction() {
-  GenericClass<int> using = aMixinReturningFunction();
+  // ignore: unused_local_variable
+  GenericClass<int>? using = aMixinReturningFunction();
 }
 
 /// A super class, with many powers. Link to [Apple] from another library.
 @deprecated
 class SuperAwesomeClass {
   /// In the super class.
-  List<String> powers;
+  List<String>? powers;
 
   /// In the super class.
   ///
   /// Another comment line.
-  void fly(int height, Cool superCool, {String msg}) {
+  void fly(int height, Cool superCool, {String? msg}) {
     // ignore: unused_local_variable, avoid_init_to_null
     var x = null;
     // ignore: unused_local_variable
@@ -435,7 +434,7 @@ class SuperAwesomeClass {
     }
   }
 
-  SuperAwesomeClass operator -(other) {
+  SuperAwesomeClass? operator -(other) {
     return null;
   }
 }
@@ -456,7 +455,12 @@ void aVoidParameter(Future<void> p1) {}
 /// This class extends Future<void>
 abstract class ExtendsFutureVoid extends Future<void> {
   // ignore: missing_return
-  factory ExtendsFutureVoid(FutureOr<void> computation()) {}
+  factory ExtendsFutureVoid(FutureOr<void> computation()) =>
+      _ExtendsFutureVoidImpl();
+}
+
+class _ExtendsFutureVoidImpl implements ExtendsFutureVoid {
+  dynamic noSuchMethod(Invocation _) => null;
 }
 
 /// This class implements Future<void>
@@ -465,7 +469,7 @@ abstract class ImplementsFutureVoid implements Future<void> {}
 /// This class takes a type, and it might be void.
 class ATypeTakingClass<T> {
   // ignore: missing_return
-  T aMethodMaybeReturningVoid() {}
+  T? aMethodMaybeReturningVoid() {}
 }
 
 class ABaseClass {}
@@ -487,13 +491,13 @@ class MixedInImplementation with MixInImplementation {}
 /// they are correct.
 class ImplicitProperties {
   /// Docs for implicitGetterExplicitSetter from ImplicitProperties.
-  String implicitGetterExplicitSetter;
+  String? implicitGetterExplicitSetter;
 
   /// Docs for explicitGetterImplicitSetter from ImplicitProperties.
-  List<int> explicitGetterImplicitSetter;
+  List<int>? explicitGetterImplicitSetter;
 
   /// A simple property to inherit.
-  int forInheriting;
+  int? forInheriting;
 
   /// @nodoc for you
   String get explicitNonDocumentedGetter => "something";
@@ -508,7 +512,7 @@ class ImplicitProperties {
   set explicitPartiallyDocumentedField(double foo) {}
 
   /// @nodoc here, you should never see this
-  String documentedPartialFieldInSubclassOnly;
+  String? documentedPartialFieldInSubclassOnly;
 
   /// Explicit getter for inheriting.
   int get explicitGetterSetterForInheriting => 12;
@@ -529,14 +533,14 @@ abstract class ClassWithUnusualProperties extends ImplicitProperties {
   @override
 
   /// Docs for setter of implicitGetterExplicitSetter.
-  set implicitGetterExplicitSetter(String x) {}
+  set implicitGetterExplicitSetter(String? x) {}
 
   @override
 
   /// Getter doc for explicitGetterImplicitSetter
-  List<int> get explicitGetterImplicitSetter => List<int>();
+  List<int> get explicitGetterImplicitSetter => List<int>.filled(1, 1);
 
-  myCoolTypedef _aFunction;
+  myCoolTypedef? _aFunction;
 
   /// Since I have a different doc, I should be documented.
   @override
@@ -544,12 +548,12 @@ abstract class ClassWithUnusualProperties extends ImplicitProperties {
 
   /// Getter doc for explicitGetterSetter.
   @Annotation('a Getter Annotation')
-  myCoolTypedef get explicitGetterSetter {
+  myCoolTypedef? get explicitGetterSetter {
     return _aFunction;
   }
 
   /// @nodoc for a simple hidden property.
-  String simpleHidden;
+  String? simpleHidden;
 
   /// @nodoc on setter
   set explicitNodocGetterSetter(String s) {}
@@ -559,10 +563,10 @@ abstract class ClassWithUnusualProperties extends ImplicitProperties {
 
   /// This property is not synthetic, so it might reference [f] -- display it.
   @Annotation('a Setter Annotation')
-  set explicitGetterSetter(myCoolTypedef f) => _aFunction = f;
+  set explicitGetterSetter(myCoolTypedef? f) => _aFunction = f;
 
   /// This property only has a getter and no setter; no parameters to print.
-  myCoolTypedef get explicitGetter {
+  myCoolTypedef? get explicitGetter {
     return _aFunction;
   }
 
@@ -572,7 +576,7 @@ abstract class ClassWithUnusualProperties extends ImplicitProperties {
   /// This property has some docs, too.
   final Set finalProperty = Set();
 
-  Map implicitReadWrite;
+  Map? implicitReadWrite;
 
   /// Hey there, more things not to warn about: [f], [x], or [q].
   String aMethod(Function f(Cool x, bool q)) {
@@ -582,13 +586,13 @@ abstract class ClassWithUnusualProperties extends ImplicitProperties {
 
 class HtmlEscapableImplicitProperties {
   /// Docs for implicitGetterExplicitSetter from HtmlEscapableImplicitProperties.
-  List<int> implicitGetterExplicitSetter;
+  List<int>? implicitGetterExplicitSetter;
 
   /// Docs for explicitGetterImplicitSetter from HtmlEscapableImplicitProperties.
-  List<int> explicitGetterImplicitSetter;
+  List<int>? explicitGetterImplicitSetter;
 
   /// A simple property to inherit.
-  List<int> forInheriting;
+  List<int>? forInheriting;
 
   /// Explicit getter for inheriting.
   List<int> get explicitGetterSetterForInheriting => [1, 2];
@@ -601,27 +605,27 @@ class HtmlEscapableProperties extends HtmlEscapableImplicitProperties {
   @override
 
   /// Docs for setter of implicitGetterExplicitSetter.
-  set implicitGetterExplicitSetter(List<int> x) {}
+  set implicitGetterExplicitSetter(List<int>? x) {}
 
   @override
 
   /// Getter doc for explicitGetterImplicitSetter
-  List<int> get explicitGetterImplicitSetter => List<int>();
+  List<int> get explicitGetterImplicitSetter => List<int>.filled(1, 1);
 
   /// Getter doc for explicitGetterSetter.
-  List<int> get explicitGetterSetter => List<int>();
+  List<int> get explicitGetterSetter => List<int>.filled(1, 1);
 
   /// Setter doc for explicitGetterSetter.
   set explicitGetterSetter(List<int> aList) {}
 
   /// A final property.
-  final List<int> finalProperty = List<int>();
+  final List<int> finalProperty = List<int>.filled(1, 1);
 
   /// A simple property.
-  List<int> simpleProperty = List<int>();
+  List<int> simpleProperty = List<int>.filled(1, 1);
 
   /// A long multiple variable declaration.
-  List<int> iAmALongLongLongLongLongLongLongLongLongName,
+  List<int>? iAmALongLongLongLongLongLongLongLongLongName,
       ensureWholeDeclarationIsVisible;
 }
 
@@ -638,7 +642,7 @@ class LongFirstLine extends SuperAwesomeClass
   static const int ANSWER = 42;
 
   /// An instance string property. Readable and writable.
-  String aStringProperty;
+  String? aStringProperty;
 
   /// A static int property.
   static int meaningOfLife = 42;
@@ -665,7 +669,7 @@ class LongFirstLine extends SuperAwesomeClass
   int twoParams(String one, two) => 42;
 
   /// One dynamic param, two named optionals.
-  bool optionalParams(first, {second, int third}) => true;
+  bool optionalParams(first, {second, int? third}) => true;
 
   /// Dynamic getter. Readable only.
   get dynamicGetter => 'could be anything';
@@ -674,12 +678,12 @@ class LongFirstLine extends SuperAwesomeClass
   void set onlySetter(double d) {}
 
   /// Adds another one of these thingies.
-  LongFirstLine operator +(LongFirstLine other) {
+  LongFirstLine? operator +(LongFirstLine other) {
     return null;
   }
 
   /// Multiplies a thingies to this thingie and then returns a new thingie.
-  LongFirstLine operator *(LongFirstLine other) {
+  LongFirstLine? operator *(LongFirstLine other) {
     return null;
   }
 
@@ -735,7 +739,7 @@ class Foo2 {
 }
 
 class OtherGenericsThing<A> {
-  HasGenerics<A, Cool, String> convert() => null;
+  HasGenerics<A, Cool, String>? convert() => null;
 }
 
 /// Constant property.
@@ -746,10 +750,10 @@ const double PI = 3.14159;
 final int meaningOfLife = 42;
 
 /// Simple property
-String simpleProperty;
+String? simpleProperty;
 
 /// Simple @nodoc property.
-String simplePropertyHidden;
+String? simplePropertyHidden;
 
 /// Setter docs should be shown.
 set getterSetterNodocGetter(int value) {}
@@ -801,7 +805,7 @@ get dynamicGetter => 'i could be anything';
 ///
 /// Thanks for using this function!
 @deprecated
-String topLevelFunction(int param1, bool param2, Cool coolBeans,
+String? topLevelFunction(int param1, bool param2, Cool coolBeans,
     [double optionalPositional = 0.0]) {
   return null;
 }
@@ -815,7 +819,7 @@ void onlyPositionalWithNoDefaultNoType([@greatestAnnotation anything]) {}
 
 /// Top-level function with 1 param and 2 optional named params, 1 with a
 /// default value.
-void soIntense(anything, {bool flag: true, int value}) {}
+void soIntense(anything, {bool flag: true, int? value}) {}
 
 /// [FooBar] comes from another library.
 void paramFromAnotherLib(Apple thing) {}
@@ -833,7 +837,7 @@ FutureOr thisIsFutureOr() => null;
 FutureOr<Null> thisIsFutureOrNull() => null;
 
 /// Explicitly return a `FutureOr<T>`.
-FutureOr<T> thisIsFutureOrT<T>() => null;
+FutureOr<T>? thisIsFutureOrT<T>() => null;
 
 /// Has a parameter explicitly typed `FutureOr<Null>`.
 void paramOfFutureOrNull(FutureOr<Null> future) {}
@@ -855,7 +859,7 @@ const greatestAnnotation = 'greatest';
 /// This function has two parameters that are functions.
 ///
 /// Check out the [number] parameter. It's the first one.
-String functionWithFunctionParameters(int number, void thing(one, two),
+String? functionWithFunctionParameters(int number, void thing(one, two),
         String string, Future asyncThing(three, four, five, six, seven)) =>
     null;
 
@@ -880,7 +884,7 @@ class WithGetterAndSetter {
 
 /// Test that we can properly handle covariant member parameters.
 class CovariantMemberParams {
-  covariant int covariantField;
+  covariant int? covariantField;
 
   set covariantSetter(covariant int x) {}
 
@@ -895,7 +899,7 @@ class HasGenericWithExtends<T extends Foo2> {}
 class SpecialList<E> extends ListBase<E> {
   // ignore: annotate_overrides
   E operator [](int index) {
-    return null;
+    return first;
   }
 
   // ignore: annotate_overrides
@@ -966,7 +970,7 @@ class BaseForDocComments {
   /// Reference to an inherited member in another library via class name: [ExtendedBaseReexported.action]
   ///
   /// Link to an existing file: [link](../SubForDocComments/localMethod.html)
-  String doAwesomeStuff(int value) => null;
+  String? doAwesomeStuff(int value) => null;
 
   void anotherMethod() {}
 
@@ -975,20 +979,20 @@ class BaseForDocComments {
 
   String operator [](String key) => "${key}'s value";
 
-  final bool initializeMe;
+  final bool? initializeMe;
 
-  int somethingShadowy;
+  int? somethingShadowy;
 
   /// I'm not really a constructor, but I'm allowed to exist anyway.
-  int aConstructorShadowed;
+  int? aConstructorShadowed;
 
-  BaseForDocComments(this.initializeMe, [bool somethingShadowy]);
+  BaseForDocComments(this.initializeMe, [bool? somethingShadowy]);
 
   BaseForDocComments.aNonDefaultConstructor(this.initializeMe);
 
   BaseForDocComments.aConstructorShadowed(this.initializeMe);
 
-  factory BaseForDocComments.aFactoryFunction() => null;
+  factory BaseForDocComments.aFactoryConstructor() => BaseForDocComments(true);
 }
 
 /// Verify that we can define and use macros inside accessors.
@@ -1030,20 +1034,20 @@ const required = 'required';
 
 /// Paints an image into the given rectangle in the canvas.
 void paintImage1(
-    {@required String canvas,
-    @required int rect,
-    @required ExtraSpecialList image,
-    BaseForDocComments colorFilter,
+    {required String canvas,
+    required int rect,
+    required ExtraSpecialList image,
+    BaseForDocComments? colorFilter,
     String repeat: LongFirstLine.THING}) {
   // nothing to do here -
 }
 
 /// Paints an image into the given rectangle in the canvas.
 void paintImage2(String fooParam,
-    [@required String canvas,
-    @required int rect,
-    @required ExtraSpecialList image,
-    BaseForDocComments colorFilter,
+    [@required String? canvas,
+    @required int? rect,
+    @required ExtraSpecialList? image,
+    BaseForDocComments? colorFilter,
     String repeat = LongFirstLine.THING]) {
   // nothing to do here -
 }
@@ -1268,7 +1272,7 @@ class Super6 implements _Super5 {}
 abstract class IntermediateAbstract extends Object {
   /// This is an override.
   @override
-  bool operator ==(Object other) {}
+  bool operator ==(Object other) => false;
 }
 
 /// This should inherit [==] from [IntermediateAbstract].
@@ -1276,9 +1280,9 @@ class IntermediateAbstractSubclass extends IntermediateAbstract {}
 
 /// Test parameter comment resolution in factory constructors and methods.
 class FactoryConstructorThings {
-  bool aName;
-  int anotherName;
-  String yetAnotherName;
+  bool? aName;
+  int? anotherName;
+  String? yetAnotherName;
   final List<String> initViaFieldFormal;
   final int fieldFormalWithDefault;
 
@@ -1286,35 +1290,35 @@ class FactoryConstructorThings {
       {this.fieldFormalWithDefault = 7});
 
   factory FactoryConstructorThings.anotherName({
-    bool aName,
-    List<int> anotherName,
-    int anotherDifferentName,
-    String differentName,
+    bool? aName,
+    List<int>? anotherName,
+    int? anotherDifferentName,
+    String? differentName,
   }) {
-    return null;
+    return FactoryConstructorThings([]);
   }
 
   factory FactoryConstructorThings.anotherConstructor({
-    bool anotherName,
-    bool redHerring,
+    bool? anotherName,
+    bool? redHerring,
   }) {
-    return null;
+    return FactoryConstructorThings([]);
   }
 
   void aMethod(bool yetAnotherName) {}
 }
 
-DTypeParam
+DTypeParam?
     aTopLevelTypeParameterFunction<DTypeParam extends TypeParameterThings>(
         DTypeParam typedParam) {}
 
 abstract class TypeParameterThings<ATypeParam,
     BTypeParam extends FactoryConstructorThings> {
-  ATypeParam aName;
-  List<BTypeParam> aThing;
+  ATypeParam? aName;
+  List<BTypeParam>? aThing;
 
   /// Here are some docs to inherit referencing [ATypeParam], [BTypeParam], and [CTypeParam].
-  BTypeParam aMethod<CTypeParam>(ATypeParam aParam, CTypeParam anotherParam);
+  BTypeParam? aMethod<CTypeParam>(ATypeParam aParam, CTypeParam anotherParam);
 }
 
 /// Test that inheriting documentation can still reference parent type
@@ -1322,7 +1326,7 @@ abstract class TypeParameterThings<ATypeParam,
 class TypeParameterThingsExtended
     extends TypeParameterThings<String, FactoryConstructorThings> {
   @override
-  FactoryConstructorThings aMethod<QTypeParam>(
+  FactoryConstructorThings? aMethod<QTypeParam>(
           String aParam, QTypeParam anotherParam) =>
       null;
 }
@@ -1333,7 +1337,7 @@ class TypeParameterThingsExtendedQ
   @override
 
   /// I override documentation so I can reference [QTypeParam].
-  FactoryConstructorThings aMethod<QTypeParam>(
+  FactoryConstructorThings? aMethod<QTypeParam>(
           String aParam, QTypeParam anotherParam) =>
       null;
 }
diff --git a/testing/test_package/lib/gadget_extender.dart b/testing/test_package/lib/gadget_extender.dart
index 74beaa273d..bbb10c3a41 100644
--- a/testing/test_package/lib/gadget_extender.dart
+++ b/testing/test_package/lib/gadget_extender.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 import 'src/gadget.dart';
 
 class GadgetExtender extends Gadget {}
diff --git a/testing/test_package/lib/implementors.dart b/testing/test_package/lib/implementors.dart
index 33d041cbde..f5c73a2425 100644
--- a/testing/test_package/lib/implementors.dart
+++ b/testing/test_package/lib/implementors.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 // A library useful to check implementer chain edge cases.
 library implementors;
 
diff --git a/testing/test_package/lib/is_deprecated.dart b/testing/test_package/lib/is_deprecated.dart
index b82532cf0f..181ce021fe 100644
--- a/testing/test_package/lib/is_deprecated.dart
+++ b/testing/test_package/lib/is_deprecated.dart
@@ -1,6 +1,4 @@
 /// This lib is deprecated. It never had a chance
 
-// @dart=2.9
-
 @deprecated
 library is_deprecated;
diff --git a/testing/test_package/lib/mylibpub.dart b/testing/test_package/lib/mylibpub.dart
index 564774587c..e4d9af04fb 100644
--- a/testing/test_package/lib/mylibpub.dart
+++ b/testing/test_package/lib/mylibpub.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library mylibpub;
 
 void helperFunction(String message, int i) => print(message);
diff --git a/testing/test_package/lib/override_class.dart b/testing/test_package/lib/override_class.dart
index d93fc1662b..3e0bee6abb 100644
--- a/testing/test_package/lib/override_class.dart
+++ b/testing/test_package/lib/override_class.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'base_class.dart';
 
 class BoxConstraints extends Constraints {
diff --git a/testing/test_package/lib/reexport_one.dart b/testing/test_package/lib/reexport_one.dart
index 6fb0913aaf..8f33931940 100644
--- a/testing/test_package/lib/reexport_one.dart
+++ b/testing/test_package/lib/reexport_one.dart
@@ -2,8 +2,6 @@
 /// {@canonicalFor reexport.somelib.AUnicornClass}
 /// {@category Unreal}
 
-// @dart=2.9
-
 library reexport_one;
 
 export 'src/somelib.dart';
diff --git a/testing/test_package/lib/reexport_three.dart b/testing/test_package/lib/reexport_three.dart
index ec5d00d2d5..10e4b1a399 100644
--- a/testing/test_package/lib/reexport_three.dart
+++ b/testing/test_package/lib/reexport_three.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library reexport_three;
 
 // Test show/hide handling.
diff --git a/testing/test_package/lib/reexport_two.dart b/testing/test_package/lib/reexport_two.dart
index 3aab944e86..383a773323 100644
--- a/testing/test_package/lib/reexport_two.dart
+++ b/testing/test_package/lib/reexport_two.dart
@@ -4,8 +4,6 @@
 /// {@canonicalFor reexport.somelib.DocumentThisExtensionOnce}
 /// {@category Unreal}
 
-// @dart=2.9
-
 library reexport_two;
 
 // Intentionally create some duplicates via reexporting.
diff --git a/testing/test_package/lib/set_literals.dart b/testing/test_package/lib/set_literals.dart
index a22b1cf63d..92ea506f30 100644
--- a/testing/test_package/lib/set_literals.dart
+++ b/testing/test_package/lib/set_literals.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 const inferredTypeSet = const {1, 3, 5};
 const Set<int> specifiedSet = const {};
 const untypedMap = const {};
diff --git a/testing/test_package/lib/src/base.dart b/testing/test_package/lib/src/base.dart
index b8df2e8ace..fcb93ea3cf 100644
--- a/testing/test_package/lib/src/base.dart
+++ b/testing/test_package/lib/src/base.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library two_exports.src.base;
 
 import '../fake.dart';
@@ -9,15 +7,15 @@ import 'local_scope.dart';
 class BaseClass extends WithGetterAndSetter {}
 
 class BaseWithMembers {
-  int aField;
+  int? aField;
 
   /// Here is some documentation that links to [aNotReexportedVariable]
   /// for documentationFrom processing.
-  bool anotherField;
+  bool? anotherField;
 
   static aStaticMethod() {}
 
-  static String aStaticField;
+  static String? aStaticField;
 
   BaseWithMembers() {}
 
diff --git a/testing/test_package/lib/src/extending.dart b/testing/test_package/lib/src/extending.dart
index 0e7bcce60c..14c9a1486b 100644
--- a/testing/test_package/lib/src/extending.dart
+++ b/testing/test_package/lib/src/extending.dart
@@ -1,12 +1,10 @@
-// @dart=2.9
-
 library two_exports.src.extending;
 
 import 'base.dart';
 
 int topLevelVariable = 1;
 
-bool someConflictingNameSymbol;
+bool? someConflictingNameSymbol;
 
 /// Extending class extends [BaseClass].
 ///
@@ -17,5 +15,5 @@ class ExtendingClass extends BaseClass {}
 
 class ExtendingAgain extends BaseWithMembers {
   @override
-  bool anotherField;
+  bool? anotherField;
 }
diff --git a/testing/test_package/lib/src/gadget.dart b/testing/test_package/lib/src/gadget.dart
index ceb7c784eb..f7054a19c4 100644
--- a/testing/test_package/lib/src/gadget.dart
+++ b/testing/test_package/lib/src/gadget.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 class _GadgetBase {
   int get gadgetGetter => 5;
 }
diff --git a/testing/test_package/lib/src/import_unusual.dart b/testing/test_package/lib/src/import_unusual.dart
index 030f71f2d9..52bb1f7fd9 100644
--- a/testing/test_package/lib/src/import_unusual.dart
+++ b/testing/test_package/lib/src/import_unusual.dart
@@ -1,5 +1,3 @@
 /// This library exists only to be imported with an unusual URI.
 
-// @dart=2.9
-
 library import_unusual;
diff --git a/testing/test_package/lib/src/intermediate_implements.dart b/testing/test_package/lib/src/intermediate_implements.dart
index e9d85c1453..fdec5c6279 100644
--- a/testing/test_package/lib/src/intermediate_implements.dart
+++ b/testing/test_package/lib/src/intermediate_implements.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 // A src-private library for intermediate classes to implement.
 library intermediate_implements;
 
diff --git a/testing/test_package/lib/src/local_scope.dart b/testing/test_package/lib/src/local_scope.dart
index 396744aef5..cf8ae36ef4 100644
--- a/testing/test_package/lib/src/local_scope.dart
+++ b/testing/test_package/lib/src/local_scope.dart
@@ -1,8 +1,6 @@
-// @dart=2.9
-
 /// Imported by a library but not reexported.
 library two_exports.src.local_scope;
 
-String aNotReexportedVariable;
+String? aNotReexportedVariable;
 
-bool anotherNotReexportedVariable;
+bool? anotherNotReexportedVariable;
diff --git a/testing/test_package/lib/src/mixins.dart b/testing/test_package/lib/src/mixins.dart
index 50c2326deb..f52a7c6d0d 100644
--- a/testing/test_package/lib/src/mixins.dart
+++ b/testing/test_package/lib/src/mixins.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library mixins;
 
 export 'mixins_base.dart';
diff --git a/testing/test_package/lib/src/mixins_base.dart b/testing/test_package/lib/src/mixins_base.dart
index 86197667e9..26646fc609 100644
--- a/testing/test_package/lib/src/mixins_base.dart
+++ b/testing/test_package/lib/src/mixins_base.dart
@@ -1,11 +1,9 @@
-// @dart=2.9
-
 library mixins_base;
 
 mixin AMixin {}
 
 class ThisClass {
-  String property;
+  String? property;
 }
 
 /// A class that extends another class with a new-style mixin, then is
diff --git a/testing/test_package/lib/src/mylib.dart b/testing/test_package/lib/src/mylib.dart
index 35c5624a7c..d9e423d539 100644
--- a/testing/test_package/lib/src/mylib.dart
+++ b/testing/test_package/lib/src/mylib.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library src.mylib;
 
 void helperFunction(String message) => print(message);
diff --git a/testing/test_package/lib/src/nodocme.dart b/testing/test_package/lib/src/nodocme.dart
index 36d9b3f4c2..707a399fb6 100644
--- a/testing/test_package/lib/src/nodocme.dart
+++ b/testing/test_package/lib/src/nodocme.dart
@@ -3,8 +3,6 @@
 /// reexported, due to dartdoc_options.yaml in the package root.
 ///
 
-// @dart=2.9
-
 library nodocme;
 
 /// I should not appear in documentation.
diff --git a/testing/test_package/lib/src/reexport_this.dart b/testing/test_package/lib/src/reexport_this.dart
index 77255cf53c..9dfaf7a1f2 100644
--- a/testing/test_package/lib/src/reexport_this.dart
+++ b/testing/test_package/lib/src/reexport_this.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library reexport_this;
 
 /// {@template example:templateMemberTest}
diff --git a/testing/test_package/lib/src/shadow_lib.dart b/testing/test_package/lib/src/shadow_lib.dart
index 57e1901e74..8afe83d6aa 100644
--- a/testing/test_package/lib/src/shadow_lib.dart
+++ b/testing/test_package/lib/src/shadow_lib.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library shadow_lib;
 
 class ADuplicateClass {
diff --git a/testing/test_package/lib/src/shadowing_lib.dart b/testing/test_package/lib/src/shadowing_lib.dart
index 72ea97805c..c3412ba1c4 100644
--- a/testing/test_package/lib/src/shadowing_lib.dart
+++ b/testing/test_package/lib/src/shadowing_lib.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library shadowing_lib;
 
 class ADuplicateClass {
diff --git a/testing/test_package/lib/src/somelib.dart b/testing/test_package/lib/src/somelib.dart
index 1bfa7e15b1..ad7f083f64 100644
--- a/testing/test_package/lib/src/somelib.dart
+++ b/testing/test_package/lib/src/somelib.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library reexport.somelib;
 
 class SomeClass {}
@@ -11,7 +9,7 @@ class YetAnotherClass {}
 class AUnicornClass {}
 
 class BaseReexported {
-  String action;
+  String? action;
 }
 
 class ExtendedBaseReexported extends BaseReexported {}
diff --git a/testing/test_package/lib/src/tool.dart b/testing/test_package/lib/src/tool.dart
index bba37f211a..d08a33dd0d 100644
--- a/testing/test_package/lib/src/tool.dart
+++ b/testing/test_package/lib/src/tool.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 library test_package.tool;
 
 abstract class PrivateLibraryToolUser {
diff --git a/testing/test_package/lib/two_exports.dart b/testing/test_package/lib/two_exports.dart
index d1773f8a5a..826fa5a989 100644
--- a/testing/test_package/lib/two_exports.dart
+++ b/testing/test_package/lib/two_exports.dart
@@ -1,13 +1,11 @@
 /// {@category Real Libraries}
 /// {@category Misc}
 
-// @dart=2.9
-
 library two_exports;
 
 export 'src/base.dart';
 export 'src/extending.dart' hide someConflictingNameSymbol;
 
-int aSymbolOnlyAvailableInExportContext;
+int? aSymbolOnlyAvailableInExportContext;
 
-bool someConflictingNameSymbol;
+bool? someConflictingNameSymbol;
diff --git a/testing/test_package/lib/unrelated_factories.dart b/testing/test_package/lib/unrelated_factories.dart
index ad11cbe132..83051acedf 100644
--- a/testing/test_package/lib/unrelated_factories.dart
+++ b/testing/test_package/lib/unrelated_factories.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 class A {
   /// A link to [AB.fromMap], [fromMap], and [AB] and [A].
   factory A.fromMap(Map<String, dynamic> map) => A._A();
diff --git a/testing/test_package/pubspec.yaml b/testing/test_package/pubspec.yaml
index 0ff1a4cc49..244d34693b 100644
--- a/testing/test_package/pubspec.yaml
+++ b/testing/test_package/pubspec.yaml
@@ -4,8 +4,8 @@ description: Best package ever.
 version: 0.0.1
 dependencies:
   meta: ^1.4.0
-  args: ^1.5.0
+  args: ^2.0.0
   test_package_imported:
     path: "../test_package_imported"
 environment:
-  sdk: '>=2.14.0-0 <3.0.0'
+  sdk: '>=2.14.0 <3.0.0'
diff --git a/testing/test_package_bad/lib/test_package_bad.dart b/testing/test_package_bad/lib/test_package_bad.dart
index 72e4c623b8..5216a07899 100644
--- a/testing/test_package_bad/lib/test_package_bad.dart
+++ b/testing/test_package_bad/lib/test_package_bad.dart
@@ -1,8 +1,10 @@
+// This library does not exist.
 import 'foo.dart';
 
 /// Some sample `dartdoc` comments here.
 void myTestFunction() {
   print('one');
   print('two');
+  // This class cannot be found.
   Foo foo = Foo('three');
 }
diff --git a/testing/test_package_imported/pubspec.yaml b/testing/test_package_imported/pubspec.yaml
index 31338a7d89..5e5478407b 100644
--- a/testing/test_package_imported/pubspec.yaml
+++ b/testing/test_package_imported/pubspec.yaml
@@ -2,4 +2,4 @@ name: test_package_imported
 description: Doomed to be imported from other packages
 version: 0.0.1
 environment:
-  sdk: '>=2.0.0-dev.68 <3.0.0'
+  sdk: '>=2.13.0 <3.0.0'