From 609f8467c4735c24bbd2f7f8537c159213873604 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:06:53 -0800
Subject: [PATCH 01/24] Fix to prevent isMock from being used in release builds

---
 .../CHANGELOG.md                              |  5 +++++
 .../lib/url_launcher_platform_interface.dart  | 20 ++++++++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
index 18d373d183f2..5ca46411c4cc 100644
--- a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
+++ b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 1.0.4
+
+* Use an assertion to ensure `isMock` is not used in release builds.
+* Prevent `noSuchMethod` from being used to bypass `isMock`.
+
 ## 1.0.3
 
 * Minor DartDoc changes and add a lint for missing DartDocs.
diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 64eeec7cae2d..d8e00dc9f83e 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -21,6 +21,8 @@ abstract class UrlLauncherPlatform {
   /// Mockito mocks are implementing this class with `implements` which is forbidden for anything
   /// other than mocks (see class docs). This property provides a backdoor for mockito mocks to
   /// skip the verification that the class isn't implemented with `implements`.
+  ///
+  /// This flag has no effect in release builds.
   @visibleForTesting
   bool get isMock => false;
 
@@ -36,9 +38,17 @@ abstract class UrlLauncherPlatform {
   // TODO(amirh): Extract common platform interface logic.
   // https://github.com/flutter/flutter/issues/43368
   static set instance(UrlLauncherPlatform instance) {
-    if (!instance.isMock) {
+    bool assertionsEnabled = false;
+    assert(() {
+      assertionsEnabled = true;
+      return true;
+    });
+    if (!assertionsEnabled || !instance.isMock) {
       try {
-        instance._verifyProvidesDefaultImplementations();
+        if (_verificationToken != instance._verifyProvidesDefaultImplementations()) {
+          throw AssertionError(
+              'Platform interfaces must not be implemented with `implements`');
+        }
       } on NoSuchMethodError catch (_) {
         throw AssertionError(
             'Platform interfaces must not be implemented with `implements`');
@@ -79,5 +89,9 @@ abstract class UrlLauncherPlatform {
   //
   // This private method is called by the instance setter, which fails if the class is
   // implemented with `implements`.
-  void _verifyProvidesDefaultImplementations() {}
+  Object _verifyProvidesDefaultImplementations() => _verificationToken;
+
+  // Private object used to determine whether  mocks from instances of  genuine  if _verifyProvidesDefaultImplementations
+  // has been overridden with noSuchMethod.
+  static Object _verificationToken = Object();
 }

From d2ff05dd6d3e881968ec8fc8e1309174c3bc428a Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:09:30 -0800
Subject: [PATCH 02/24] update pubspec

---
 .../url_launcher/url_launcher_platform_interface/pubspec.yaml   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/pubspec.yaml b/packages/url_launcher/url_launcher_platform_interface/pubspec.yaml
index 3f7aa4832c41..9793c2b6f3cc 100644
--- a/packages/url_launcher/url_launcher_platform_interface/pubspec.yaml
+++ b/packages/url_launcher/url_launcher_platform_interface/pubspec.yaml
@@ -4,7 +4,7 @@ author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/url_launcher/url_launcher_platform_interface
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 1.0.3
+version: 1.0.4
 
 dependencies:
   flutter:

From ecf964d0e56fe61e5ca044208d52fe0c6928f7c8 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:10:12 -0800
Subject: [PATCH 03/24] Fix assertion

---
 .../lib/url_launcher_platform_interface.dart                    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index d8e00dc9f83e..9ce5e4ca3647 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -42,7 +42,7 @@ abstract class UrlLauncherPlatform {
     assert(() {
       assertionsEnabled = true;
       return true;
-    });
+    }());
     if (!assertionsEnabled || !instance.isMock) {
       try {
         if (_verificationToken != instance._verifyProvidesDefaultImplementations()) {

From 69a06fe0f956bd3f9da7523ce6f849f95a44bc4a Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:13:21 -0800
Subject: [PATCH 04/24] Fix comment

---
 .../lib/url_launcher_platform_interface.dart                  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 9ce5e4ca3647..4c058d0ba2ca 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -91,7 +91,7 @@ abstract class UrlLauncherPlatform {
   // implemented with `implements`.
   Object _verifyProvidesDefaultImplementations() => _verificationToken;
 
-  // Private object used to determine whether  mocks from instances of  genuine  if _verifyProvidesDefaultImplementations
-  // has been overridden with noSuchMethod.
+  // Private object used to determine if `_verifyProvidesDefaultImplementations`
+  // has been overridden with `noSuchMethod`.
   static Object _verificationToken = Object();
 }

From 0f2dd57eb243d60523a5be4bdb9526e388690303 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:26:29 -0800
Subject: [PATCH 05/24] Update CHANGELOG

---
 .../url_launcher/url_launcher_platform_interface/CHANGELOG.md  | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
index 5ca46411c4cc..f5b8d04b9cd0 100644
--- a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
+++ b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
@@ -1,7 +1,8 @@
 ## 1.0.4
 
 * Use an assertion to ensure `isMock` is not used in release builds.
-* Prevent `noSuchMethod` from being used to bypass `isMock`.
+* Prevent `noSuchMethod` from being used to bypass checks that
+  `UrlLauncherPlatform` isn't implemented with `implements`.
 
 ## 1.0.3
 

From 85b233ef75a81249eabce05b64ffd9ae13207bea Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:29:24 -0800
Subject: [PATCH 06/24] use `identical`

---
 .../lib/url_launcher_platform_interface.dart                   | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 4c058d0ba2ca..37fb8ce69c50 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -45,7 +45,8 @@ abstract class UrlLauncherPlatform {
     }());
     if (!assertionsEnabled || !instance.isMock) {
       try {
-        if (_verificationToken != instance._verifyProvidesDefaultImplementations()) {
+        if (identical(_verificationToken,
+            instance._verifyProvidesDefaultImplementations())) {
           throw AssertionError(
               'Platform interfaces must not be implemented with `implements`');
         }

From 6941bf5a90ce0234a2f8e09431459e0c886bb245 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:35:53 -0800
Subject: [PATCH 07/24] Make `Object` const and fix test

---
 .../lib/url_launcher_platform_interface.dart                  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 37fb8ce69c50..06828d5f46c2 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -45,7 +45,7 @@ abstract class UrlLauncherPlatform {
     }());
     if (!assertionsEnabled || !instance.isMock) {
       try {
-        if (identical(_verificationToken,
+        if (!identical(_verificationToken,
             instance._verifyProvidesDefaultImplementations())) {
           throw AssertionError(
               'Platform interfaces must not be implemented with `implements`');
@@ -94,5 +94,5 @@ abstract class UrlLauncherPlatform {
 
   // Private object used to determine if `_verifyProvidesDefaultImplementations`
   // has been overridden with `noSuchMethod`.
-  static Object _verificationToken = Object();
+  static const Object _verificationToken = const Object();
 }

From 5762a2d47939090b9b5a3ea27d87b1a182068279 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 12:39:47 -0800
Subject: [PATCH 08/24] Update comment

---
 .../lib/url_launcher_platform_interface.dart                  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 06828d5f46c2..0f9ab9fde4b6 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -92,7 +92,7 @@ abstract class UrlLauncherPlatform {
   // implemented with `implements`.
   Object _verifyProvidesDefaultImplementations() => _verificationToken;
 
-  // Private object used to determine if `_verifyProvidesDefaultImplementations`
-  // has been overridden with `noSuchMethod`.
+  // Private object used to ensure that `_verifyProvidesDefaultImplementations`
+  // cannot be implemented using `noSuchMethod`.
   static const Object _verificationToken = const Object();
 }

From fff7923689851ca23a0c01c78a0448c32dee8435 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:15:06 -0800
Subject: [PATCH 09/24] Alternative approach

---
 .../url_launcher/test/url_launcher_test.dart  |  3 +-
 .../lib/url_launcher_platform_interface.dart  | 99 +++++++++++--------
 .../method_channel_url_launcher_test.dart     |  6 +-
 3 files changed, 64 insertions(+), 44 deletions(-)

diff --git a/packages/url_launcher/url_launcher/test/url_launcher_test.dart b/packages/url_launcher/url_launcher/test/url_launcher_test.dart
index 2481e5a0ee63..861b18e06625 100644
--- a/packages/url_launcher/url_launcher/test/url_launcher_test.dart
+++ b/packages/url_launcher/url_launcher/test/url_launcher_test.dart
@@ -13,7 +13,6 @@ import 'package:flutter/services.dart' show PlatformException;
 
 void main() {
   final MockUrlLauncher mock = MockUrlLauncher();
-  when(mock.isMock).thenReturn(true);
   UrlLauncherPlatform.instance = mock;
 
   test('closeWebView default behavior', () async {
@@ -208,4 +207,4 @@ void main() {
   });
 }
 
-class MockUrlLauncher extends Mock implements UrlLauncherPlatform {}
+class MockUrlLauncher extends Mock with MockPlatformInterface implements UrlLauncherPlatform {}
diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 0f9ab9fde4b6..d6e3d5c902c8 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -8,6 +8,61 @@ import 'package:meta/meta.dart' show required, visibleForTesting;
 
 import 'method_channel_url_launcher.dart';
 
+/// Base class for platform interfaces.
+///
+/// Provides helper methods for ensuring that platform interfaces are
+/// implemented using `extends` instead of `implements`.
+class PlatformInterface {
+  PlatformInterface({ Object token }) : _verificationToken = token;
+
+  final Object _token;
+
+  // Mock implementations can return true here using `noSuchMethod`.
+  //
+  // Mockito mocks are implementing this class with `implements` which is forbidden for anything
+  // other than mocks (see class docs). This property provides `MockPlatformInterface`
+  // a backdoor for mockito mocks to skip the verification that the class isn't
+  // implemented with `implements`.
+  bool get _isMock => false;
+
+  /// Returns the instance.
+  static void verifyToken<T>(Object token, PlatformInterface instance) {
+    assert(identical(token, instance._token));
+  }
+
+  // This method makes sure that UrlLauncher isn't implemented with `implements`.
+  //
+  // See class doc for more details on why implementing this class is forbidden.
+  //
+  // This private method is called by the instance setter, which fails if the class is
+  // implemented with `implements`.
+  Object _verifyProvidesDefaultImplementations() => _verificationToken;
+
+  // Private object used to ensure that `_verifyProvidesDefaultImplementations`
+  // cannot be implemented using `noSuchMethod`.
+  static const Object _verificationToken = const Object();
+}
+
+/// A [PlatformInterface] that can be mocked with mockito.
+///
+/// Throws an `AssertionError` when used in release builds.
+@visibleForTesting
+class MockPlatformInterface extends PlatformInterface {
+  @override
+  bool get _isMock {
+    bool assertionsEnabled = false;
+    assert(() {
+      assertionsEnabled = true;
+      return true;
+    }());
+    if (!assertionsEnabled) {
+      throw AssertionError(
+          '`MockPlatformInterface` is not intended for use in release builds.');
+    }
+    return true;
+  }
+}
+
 /// The interface that implementations of url_launcher must implement.
 ///
 /// Platform implementations should extend this class rather than implement it as `url_launcher`
@@ -15,19 +70,13 @@ import 'method_channel_url_launcher.dart';
 /// (using `extends`) ensures that the subclass will get the default implementation, while
 /// platform implementations that `implements` this interface will be broken by newly added
 /// [UrlLauncherPlatform] methods.
-abstract class UrlLauncherPlatform {
-  /// Only mock implementations should set this to true.
-  ///
-  /// Mockito mocks are implementing this class with `implements` which is forbidden for anything
-  /// other than mocks (see class docs). This property provides a backdoor for mockito mocks to
-  /// skip the verification that the class isn't implemented with `implements`.
-  ///
-  /// This flag has no effect in release builds.
-  @visibleForTesting
-  bool get isMock => false;
+abstract class UrlLauncherPlatform extends PlatformInterface {
+  UrlLauncherPlatform() : super(token: _token);
 
   static UrlLauncherPlatform _instance = MethodChannelUrlLauncher();
 
+  static const Object _token = const Object();
+
   /// The default instance of [UrlLauncherPlatform] to use.
   ///
   /// Defaults to [MethodChannelUrlLauncher].
@@ -38,23 +87,7 @@ abstract class UrlLauncherPlatform {
   // TODO(amirh): Extract common platform interface logic.
   // https://github.com/flutter/flutter/issues/43368
   static set instance(UrlLauncherPlatform instance) {
-    bool assertionsEnabled = false;
-    assert(() {
-      assertionsEnabled = true;
-      return true;
-    }());
-    if (!assertionsEnabled || !instance.isMock) {
-      try {
-        if (!identical(_verificationToken,
-            instance._verifyProvidesDefaultImplementations())) {
-          throw AssertionError(
-              'Platform interfaces must not be implemented with `implements`');
-        }
-      } on NoSuchMethodError catch (_) {
-        throw AssertionError(
-            'Platform interfaces must not be implemented with `implements`');
-      }
-    }
+    PlatformInterface.verifyToken(_token, instance);
     _instance = instance;
   }
 
@@ -83,16 +116,4 @@ abstract class UrlLauncherPlatform {
   Future<void> closeWebView() {
     throw UnimplementedError('closeWebView() has not been implemented.');
   }
-
-  // This method makes sure that UrlLauncher isn't implemented with `implements`.
-  //
-  // See class doc for more details on why implementing this class is forbidden.
-  //
-  // This private method is called by the instance setter, which fails if the class is
-  // implemented with `implements`.
-  Object _verifyProvidesDefaultImplementations() => _verificationToken;
-
-  // Private object used to ensure that `_verifyProvidesDefaultImplementations`
-  // cannot be implemented using `noSuchMethod`.
-  static const Object _verificationToken = const Object();
 }
diff --git a/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart b/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
index 1d6b0c9f3f8c..2f511d871d3d 100644
--- a/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
@@ -27,7 +27,6 @@ void main() {
     test('Can be mocked with `implements`', () {
       final ImplementsUrlLauncherPlatform mock =
           ImplementsUrlLauncherPlatform();
-      when(mock.isMock).thenReturn(true);
       UrlLauncherPlatform.instance = mock;
     });
 
@@ -280,7 +279,8 @@ void main() {
   });
 }
 
-class ImplementsUrlLauncherPlatform extends Mock
-    implements UrlLauncherPlatform {}
+class ImplementsUrlLauncherPlatform extends Mock with MockPlatformInterface
+    implements UrlLauncherPlatform {
+}
 
 class ExtendsUrlLauncherPlatform extends UrlLauncherPlatform {}

From 5f04abd5814ed1333e0d59cb57d5b16a7680c9b4 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:25:12 -0800
Subject: [PATCH 10/24] More improvements

---
 .../lib/url_launcher_platform_interface.dart  | 25 ++++++-------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index d6e3d5c902c8..ffa6d2d66aa1 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -13,8 +13,9 @@ import 'method_channel_url_launcher.dart';
 /// Provides helper methods for ensuring that platform interfaces are
 /// implemented using `extends` instead of `implements`.
 class PlatformInterface {
-  PlatformInterface({ Object token }) : _verificationToken = token;
+  PlatformInterface({ Object token }) : _token = token;
 
+  // Pass a `const Object()` here to distinguish
   final Object _token;
 
   // Mock implementations can return true here using `noSuchMethod`.
@@ -25,22 +26,12 @@ class PlatformInterface {
   // implemented with `implements`.
   bool get _isMock => false;
 
-  /// Returns the instance.
-  static void verifyToken<T>(Object token, PlatformInterface instance) {
-    assert(identical(token, instance._token));
+  /// Return true if the platform instance has a token that matches the
+  /// provided token. This is used to ensure that implementers are using
+  /// `extends` rather than `implements`.
+  static bool isValid(PlatformInterface instance, Object token) {
+    return _isMock || identical(token, instance._token);
   }
-
-  // This method makes sure that UrlLauncher isn't implemented with `implements`.
-  //
-  // See class doc for more details on why implementing this class is forbidden.
-  //
-  // This private method is called by the instance setter, which fails if the class is
-  // implemented with `implements`.
-  Object _verifyProvidesDefaultImplementations() => _verificationToken;
-
-  // Private object used to ensure that `_verifyProvidesDefaultImplementations`
-  // cannot be implemented using `noSuchMethod`.
-  static const Object _verificationToken = const Object();
 }
 
 /// A [PlatformInterface] that can be mocked with mockito.
@@ -87,7 +78,7 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
   // TODO(amirh): Extract common platform interface logic.
   // https://github.com/flutter/flutter/issues/43368
   static set instance(UrlLauncherPlatform instance) {
-    PlatformInterface.verifyToken(_token, instance);
+    assert(PlatformInterface.isValid(instance, _token));
     _instance = instance;
   }
 

From 4b31918d062f49e796e9a11eb8ea5e77d170ff23 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:29:23 -0800
Subject: [PATCH 11/24] Fix tests

---
 .../lib/url_launcher_platform_interface.dart        |  8 +++++---
 .../test/method_channel_url_launcher_test.dart      | 13 ++++++++-----
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index ffa6d2d66aa1..7e90bc83f983 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -13,10 +13,10 @@ import 'method_channel_url_launcher.dart';
 /// Provides helper methods for ensuring that platform interfaces are
 /// implemented using `extends` instead of `implements`.
 class PlatformInterface {
-  PlatformInterface({ Object token }) : _token = token;
+  PlatformInterface({Object token}) : _instanceToken = token;
 
   // Pass a `const Object()` here to distinguish
-  final Object _token;
+  final Object _instanceToken;
 
   // Mock implementations can return true here using `noSuchMethod`.
   //
@@ -29,8 +29,10 @@ class PlatformInterface {
   /// Return true if the platform instance has a token that matches the
   /// provided token. This is used to ensure that implementers are using
   /// `extends` rather than `implements`.
+  ///
+  /// Subclasses of [MockPlatformInterface] are assumed to be valid.
   static bool isValid(PlatformInterface instance, Object token) {
-    return _isMock || identical(token, instance._token);
+    return instance._isMock || identical(token, instance._instanceToken);
   }
 }
 
diff --git a/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart b/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
index 2f511d871d3d..6c9334f6c524 100644
--- a/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart
@@ -25,8 +25,8 @@ void main() {
     });
 
     test('Can be mocked with `implements`', () {
-      final ImplementsUrlLauncherPlatform mock =
-          ImplementsUrlLauncherPlatform();
+      final UrlLauncherPlatform mock =
+          ImplementsUrlLauncherPlatformUsingMockPlatformInterface();
       UrlLauncherPlatform.instance = mock;
     });
 
@@ -279,8 +279,11 @@ void main() {
   });
 }
 
-class ImplementsUrlLauncherPlatform extends Mock with MockPlatformInterface
-    implements UrlLauncherPlatform {
-}
+class ImplementsUrlLauncherPlatform extends Mock
+    implements UrlLauncherPlatform {}
+
+class ImplementsUrlLauncherPlatformUsingMockPlatformInterface extends Mock
+    with MockPlatformInterface
+    implements UrlLauncherPlatform {}
 
 class ExtendsUrlLauncherPlatform extends UrlLauncherPlatform {}

From b170b933df8e66d7329294ab0538972ad0b38f3b Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:31:21 -0800
Subject: [PATCH 12/24] CHANGELOG

---
 .../url_launcher_platform_interface/CHANGELOG.md             | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
index f5b8d04b9cd0..a58dbcd4aa8a 100644
--- a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
+++ b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
@@ -1,8 +1,7 @@
 ## 1.0.4
 
-* Use an assertion to ensure `isMock` is not used in release builds.
-* Prevent `noSuchMethod` from being used to bypass checks that
-  `UrlLauncherPlatform` isn't implemented with `implements`.
+* Remove `@visibleForTesting` API `isMock`.
+* Introduces `MockPlatformInterface` and `PlatformInterface`.
 
 ## 1.0.3
 

From df9b2f8ebe69e200972d8670eddc0c79c53de4e1 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:32:15 -0800
Subject: [PATCH 13/24] Move comment

---
 .../lib/url_launcher_platform_interface.dart                  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 7e90bc83f983..a8d3508fdeae 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -12,6 +12,8 @@ import 'method_channel_url_launcher.dart';
 ///
 /// Provides helper methods for ensuring that platform interfaces are
 /// implemented using `extends` instead of `implements`.
+// TODO(amirh): Extract common platform interface logic.
+// https://github.com/flutter/flutter/issues/43368
 class PlatformInterface {
   PlatformInterface({Object token}) : _instanceToken = token;
 
@@ -77,8 +79,6 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
 
   /// Platform-specific plugins should set this with their own platform-specific
   /// class that extends [UrlLauncherPlatform] when they register themselves.
-  // TODO(amirh): Extract common platform interface logic.
-  // https://github.com/flutter/flutter/issues/43368
   static set instance(UrlLauncherPlatform instance) {
     assert(PlatformInterface.isValid(instance, _token));
     _instance = instance;

From 12bebdf5357597741249959b5fa6eb565448ee80 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:40:50 -0800
Subject: [PATCH 14/24] Update comments

---
 .../lib/url_launcher_platform_interface.dart         | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index a8d3508fdeae..90418f9b346d 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -10,14 +10,14 @@ import 'method_channel_url_launcher.dart';
 
 /// Base class for platform interfaces.
 ///
-/// Provides helper methods for ensuring that platform interfaces are
+/// Provides a static helper method for ensuring that platform interfaces are
 /// implemented using `extends` instead of `implements`.
 // TODO(amirh): Extract common platform interface logic.
 // https://github.com/flutter/flutter/issues/43368
-class PlatformInterface {
+abstract class PlatformInterface {
+  /// Pass a class-specific `const Object()` as the `token`.
   PlatformInterface({Object token}) : _instanceToken = token;
 
-  // Pass a `const Object()` here to distinguish
   final Object _instanceToken;
 
   // Mock implementations can return true here using `noSuchMethod`.
@@ -38,11 +38,13 @@ class PlatformInterface {
   }
 }
 
-/// A [PlatformInterface] that can be mocked with mockito.
+/// A [PlatformInterface] mixin that can be combined with mockito's `Mock`.
+///
+/// It always returns true when passed to [PlatformInterface.isValid].
 ///
 /// Throws an `AssertionError` when used in release builds.
 @visibleForTesting
-class MockPlatformInterface extends PlatformInterface {
+abstract class MockPlatformInterface extends PlatformInterface {
   @override
   bool get _isMock {
     bool assertionsEnabled = false;

From a3ad7a33cfba17e71526653a77ee14fb8a42e811 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:49:35 -0800
Subject: [PATCH 15/24] Update to syntax

---
 .../lib/url_launcher_platform_interface.dart                | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 90418f9b346d..76a8bd672318 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -16,7 +16,7 @@ import 'method_channel_url_launcher.dart';
 // https://github.com/flutter/flutter/issues/43368
 abstract class PlatformInterface {
   /// Pass a class-specific `const Object()` as the `token`.
-  PlatformInterface({Object token}) : _instanceToken = token;
+  PlatformInterface({ @required Object token }) : _instanceToken = token;
 
   final Object _instanceToken;
 
@@ -42,9 +42,9 @@ abstract class PlatformInterface {
 ///
 /// It always returns true when passed to [PlatformInterface.isValid].
 ///
-/// Throws an `AssertionError` when used in release builds.
+/// For use in testing only. Throws `AssertionError` when used in release mode.
 @visibleForTesting
-abstract class MockPlatformInterface extends PlatformInterface {
+abstract class MockPlatformInterface implements PlatformInterface {
   @override
   bool get _isMock {
     bool assertionsEnabled = false;

From 2bd58286a0e678dc9a42aad1be11c0087ff835c2 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:50:06 -0800
Subject: [PATCH 16/24] Format

---
 .../lib/url_launcher_platform_interface.dart                    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 76a8bd672318..772f192fb02b 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -16,7 +16,7 @@ import 'method_channel_url_launcher.dart';
 // https://github.com/flutter/flutter/issues/43368
 abstract class PlatformInterface {
   /// Pass a class-specific `const Object()` as the `token`.
-  PlatformInterface({ @required Object token }) : _instanceToken = token;
+  PlatformInterface({@required Object token}) : _instanceToken = token;
 
   final Object _instanceToken;
 

From 4fe61d0ac1c585a0b0bac95af64e376548038459 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 14:56:15 -0800
Subject: [PATCH 17/24] Defend against noSuchMethod

---
 .../lib/url_launcher_platform_interface.dart  | 38 +++++++++----------
 1 file changed, 17 insertions(+), 21 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 772f192fb02b..17191f7ae0e6 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -20,21 +20,26 @@ abstract class PlatformInterface {
 
   final Object _instanceToken;
 
-  // Mock implementations can return true here using `noSuchMethod`.
-  //
-  // Mockito mocks are implementing this class with `implements` which is forbidden for anything
-  // other than mocks (see class docs). This property provides `MockPlatformInterface`
-  // a backdoor for mockito mocks to skip the verification that the class isn't
-  // implemented with `implements`.
-  bool get _isMock => false;
-
   /// Return true if the platform instance has a token that matches the
   /// provided token. This is used to ensure that implementers are using
   /// `extends` rather than `implements`.
   ///
   /// Subclasses of [MockPlatformInterface] are assumed to be valid.
   static bool isValid(PlatformInterface instance, Object token) {
-    return instance._isMock || identical(token, instance._instanceToken);
+    if (identical(instance._instanceToken, MockPlatformInterface._token)) {
+      bool assertionsEnabled = false;
+      assert(() {
+        assertionsEnabled = true;
+        return true;
+      }());
+      if (!assertionsEnabled) {
+        throw AssertionError(
+            '`MockPlatformInterface` is not intended for use in release builds.');
+      } else {
+        return true;
+      }
+    }
+    return identical(token, instance._instanceToken);
   }
 }
 
@@ -45,19 +50,10 @@ abstract class PlatformInterface {
 /// For use in testing only. Throws `AssertionError` when used in release mode.
 @visibleForTesting
 abstract class MockPlatformInterface implements PlatformInterface {
+  static const Object _token = const Object();
+
   @override
-  bool get _isMock {
-    bool assertionsEnabled = false;
-    assert(() {
-      assertionsEnabled = true;
-      return true;
-    }());
-    if (!assertionsEnabled) {
-      throw AssertionError(
-          '`MockPlatformInterface` is not intended for use in release builds.');
-    }
-    return true;
-  }
+  final Object _instanceToken = _token;
 }
 
 /// The interface that implementations of url_launcher must implement.

From 8a4a3774d2f2b6398a0e1b330f4d45e15a536ed1 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:01:47 -0800
Subject: [PATCH 18/24] Flip if statement

---
 .../lib/url_launcher_platform_interface.dart                | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 17191f7ae0e6..1d3aff4aa4f5 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -32,11 +32,11 @@ abstract class PlatformInterface {
         assertionsEnabled = true;
         return true;
       }());
-      if (!assertionsEnabled) {
+      if (assertionsEnabled) {
+        return true;
+      } else {
         throw AssertionError(
             '`MockPlatformInterface` is not intended for use in release builds.');
-      } else {
-        return true;
       }
     }
     return identical(token, instance._instanceToken);

From 335f098b5a7872a31ec207508fa5852992d5fcb7 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:03:46 -0800
Subject: [PATCH 19/24] Clean up comments more

---
 .../lib/url_launcher_platform_interface.dart           | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 1d3aff4aa4f5..fc05964c0853 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -20,9 +20,11 @@ abstract class PlatformInterface {
 
   final Object _instanceToken;
 
-  /// Return true if the platform instance has a token that matches the
-  /// provided token. This is used to ensure that implementers are using
-  /// `extends` rather than `implements`.
+  /// Return `true `if the platform instance has a token that matches the
+  /// provided token.
+  /// 
+  /// This is used to ensure that implementers are using `extends` rather than
+  /// `implements`.
   ///
   /// Subclasses of [MockPlatformInterface] are assumed to be valid.
   static bool isValid(PlatformInterface instance, Object token) {
@@ -45,7 +47,7 @@ abstract class PlatformInterface {
 
 /// A [PlatformInterface] mixin that can be combined with mockito's `Mock`.
 ///
-/// It always returns true when passed to [PlatformInterface.isValid].
+/// It always returns `true` when passed to [PlatformInterface.isValid].
 ///
 /// For use in testing only. Throws `AssertionError` when used in release mode.
 @visibleForTesting

From 556ce46907dd7389f7788c31b6ef5757967f8eff Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:08:03 -0800
Subject: [PATCH 20/24] Move assertion logic into MockPlatformInterface

---
 .../lib/url_launcher_platform_interface.dart  | 26 ++++++++++---------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index fc05964c0853..61f1c9c5506b 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -29,17 +29,7 @@ abstract class PlatformInterface {
   /// Subclasses of [MockPlatformInterface] are assumed to be valid.
   static bool isValid(PlatformInterface instance, Object token) {
     if (identical(instance._instanceToken, MockPlatformInterface._token)) {
-      bool assertionsEnabled = false;
-      assert(() {
-        assertionsEnabled = true;
-        return true;
-      }());
-      if (assertionsEnabled) {
-        return true;
-      } else {
-        throw AssertionError(
-            '`MockPlatformInterface` is not intended for use in release builds.');
-      }
+      return true;
     }
     return identical(token, instance._instanceToken);
   }
@@ -55,7 +45,19 @@ abstract class MockPlatformInterface implements PlatformInterface {
   static const Object _token = const Object();
 
   @override
-  final Object _instanceToken = _token;
+  Object get _instanceToken {
+    bool assertionsEnabled = false;
+    assert(() {
+      assertionsEnabled = true;
+      return true;
+    }());
+    if (assertionsEnabled) {
+      return _token;
+    } else {
+      throw AssertionError(
+          '`MockPlatformInterface` is not intended for use in release builds.');
+    }
+  }
 }
 
 /// The interface that implementations of url_launcher must implement.

From 86b8d3d956f82a22c09a35af5a7f8ad9fbb2b52c Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:32:39 -0800
Subject: [PATCH 21/24] feedback from Amir

---
 .../CHANGELOG.md                              |  2 +-
 .../lib/url_launcher_platform_interface.dart  | 42 ++++++++++---------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
index a58dbcd4aa8a..f12ad149e05a 100644
--- a/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
+++ b/packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md
@@ -1,7 +1,7 @@
 ## 1.0.4
 
 * Remove `@visibleForTesting` API `isMock`.
-* Introduces `MockPlatformInterface` and `PlatformInterface`.
+* Introduces `MockPlatformInterface` and `PlatformInterface` classes.
 
 ## 1.0.3
 
diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 61f1c9c5506b..89f23d5454ee 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -15,23 +15,37 @@ import 'method_channel_url_launcher.dart';
 // TODO(amirh): Extract common platform interface logic.
 // https://github.com/flutter/flutter/issues/43368
 abstract class PlatformInterface {
-  /// Pass a class-specific `const Object()` as the `token`.
+  /// Pass a private, class-specific `const Object()` as the `token`.
   PlatformInterface({@required Object token}) : _instanceToken = token;
 
   final Object _instanceToken;
 
-  /// Return `true `if the platform instance has a token that matches the
-  /// provided token.
+  /// Ensures that the platform instance has a token that matches the
+  /// provided token and throws [AssertionError] if not.
   /// 
   /// This is used to ensure that implementers are using `extends` rather than
   /// `implements`.
   ///
   /// Subclasses of [MockPlatformInterface] are assumed to be valid.
-  static bool isValid(PlatformInterface instance, Object token) {
+  ///
+  /// This is implemented as a static method so that it cannot be overridden
+  /// with `noSuchMethod`.
+  static void verifyToken(PlatformInterface instance, Object token) {
     if (identical(instance._instanceToken, MockPlatformInterface._token)) {
-      return true;
+      bool assertionsEnabled = false;
+      assert(() {
+        assertionsEnabled = true;
+        return true;
+      }());
+      if (!assertionsEnabled) {
+        throw AssertionError(
+            '`MockPlatformInterface` is not intended for use in release builds.');
+      }
+    }
+    if (!identical(token, instance._instanceToken)) {
+      throw AssertionError(
+          'Platform interfaces must not be implemented with `implements`');
     }
-    return identical(token, instance._instanceToken);
   }
 }
 
@@ -45,19 +59,7 @@ abstract class MockPlatformInterface implements PlatformInterface {
   static const Object _token = const Object();
 
   @override
-  Object get _instanceToken {
-    bool assertionsEnabled = false;
-    assert(() {
-      assertionsEnabled = true;
-      return true;
-    }());
-    if (assertionsEnabled) {
-      return _token;
-    } else {
-      throw AssertionError(
-          '`MockPlatformInterface` is not intended for use in release builds.');
-    }
-  }
+  Object get _instanceToken => _token;
 }
 
 /// The interface that implementations of url_launcher must implement.
@@ -82,7 +84,7 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
   /// Platform-specific plugins should set this with their own platform-specific
   /// class that extends [UrlLauncherPlatform] when they register themselves.
   static set instance(UrlLauncherPlatform instance) {
-    assert(PlatformInterface.isValid(instance, _token));
+    PlatformInterface.verifyToken(instance, _token);
     _instance = instance;
   }
 

From 512077e02a28c0a8fac40229232e37fd5244ae2d Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:33:05 -0800
Subject: [PATCH 22/24] Reformat

---
 .../lib/url_launcher_platform_interface.dart                    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 89f23d5454ee..1ae48fdb95ad 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -22,7 +22,7 @@ abstract class PlatformInterface {
 
   /// Ensures that the platform instance has a token that matches the
   /// provided token and throws [AssertionError] if not.
-  /// 
+  ///
   /// This is used to ensure that implementers are using `extends` rather than
   /// `implements`.
   ///

From 3d566179f6d64cedecdafdff184c29703224b304 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:37:08 -0800
Subject: [PATCH 23/24] Update comments

---
 .../lib/url_launcher_platform_interface.dart              | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 1ae48fdb95ad..8467f370a62f 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -26,7 +26,8 @@ abstract class PlatformInterface {
   /// This is used to ensure that implementers are using `extends` rather than
   /// `implements`.
   ///
-  /// Subclasses of [MockPlatformInterface] are assumed to be valid.
+  /// Subclasses of [MockPlatformInterface] are assumed to be valid in debug
+  /// builds.
   ///
   /// This is implemented as a static method so that it cannot be overridden
   /// with `noSuchMethod`.
@@ -51,9 +52,10 @@ abstract class PlatformInterface {
 
 /// A [PlatformInterface] mixin that can be combined with mockito's `Mock`.
 ///
-/// It always returns `true` when passed to [PlatformInterface.isValid].
+/// It passes the [PlatformInterface.verifyToken] check even though it isn't
+/// using `extends`.
 ///
-/// For use in testing only. Throws `AssertionError` when used in release mode.
+/// This class is intended for use in tests only.
 @visibleForTesting
 abstract class MockPlatformInterface implements PlatformInterface {
   static const Object _token = const Object();

From 144ea9d9a6afd5618c8556a31c8ac23b3f018b94 Mon Sep 17 00:00:00 2001
From: Collin Jackson <jackson@google.com>
Date: Wed, 27 Nov 2019 15:38:57 -0800
Subject: [PATCH 24/24] Fix analyzer

---
 .../lib/url_launcher_platform_interface.dart                  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
index 8467f370a62f..cfad2f87bf90 100644
--- a/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
+++ b/packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart
@@ -58,7 +58,7 @@ abstract class PlatformInterface {
 /// This class is intended for use in tests only.
 @visibleForTesting
 abstract class MockPlatformInterface implements PlatformInterface {
-  static const Object _token = const Object();
+  static const Object _token = Object();
 
   @override
   Object get _instanceToken => _token;
@@ -76,7 +76,7 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
 
   static UrlLauncherPlatform _instance = MethodChannelUrlLauncher();
 
-  static const Object _token = const Object();
+  static const Object _token = Object();
 
   /// The default instance of [UrlLauncherPlatform] to use.
   ///