diff --git a/lib/src/errors.dart b/lib/src/errors.dart
index 8940590..34f6787 100644
--- a/lib/src/errors.dart
+++ b/lib/src/errors.dart
@@ -1,5 +1,5 @@
 /// Used to notify unexpected errors
-class StockError extends Error {
+final class StockError extends Error {
   /// Constructor
   StockError(this.message);
 
diff --git a/lib/src/fetcher.dart b/lib/src/fetcher.dart
index fdd7528..88ec78b 100644
--- a/lib/src/fetcher.dart
+++ b/lib/src/fetcher.dart
@@ -12,9 +12,7 @@ import 'package:stock/src/stock_response.dart';
 /// See [ofFuture] for easily translating from a regular `Future` function.
 /// See [ofStream], for easily translating to [StockResponse] (and
 /// automatically transforming exceptions into [StockResponseError]).
-abstract class Fetcher<Key, T> {
-  Fetcher._();
-
+base class Fetcher<Key, T> {
   /// "Creates" a [Fetcher] from a [futureFactory] and translates the results
   /// into a [StockResponse].
   ///
diff --git a/lib/src/implementations/factory_fetcher.dart b/lib/src/implementations/factory_fetcher.dart
index 58d1d94..0209991 100644
--- a/lib/src/implementations/factory_fetcher.dart
+++ b/lib/src/implementations/factory_fetcher.dart
@@ -2,17 +2,17 @@
 
 import 'package:stock/src/fetcher.dart';
 
-class FactoryFetcher<Key, Output> implements Fetcher<Key, Output> {
+sealed class FactoryFetcher<Key, Output> extends Fetcher<Key, Output> {
   FactoryFetcher(this.factory);
 
   Stream<Output> Function(Key key) factory;
 }
 
-class FutureFetcher<Key, Output> extends FactoryFetcher<Key, Output> {
+final class FutureFetcher<Key, Output> extends FactoryFetcher<Key, Output> {
   FutureFetcher(Future<Output> Function(Key key) factory)
       : super((key) => Stream.fromFuture(factory(key)));
 }
 
-class StreamFetcher<Key, Output> extends FactoryFetcher<Key, Output> {
+final class StreamFetcher<Key, Output> extends FactoryFetcher<Key, Output> {
   StreamFetcher(super.factory);
 }
diff --git a/lib/src/implementations/source_of_truth_impl.dart b/lib/src/implementations/source_of_truth_impl.dart
index 85120ba..5eca7fe 100644
--- a/lib/src/implementations/source_of_truth_impl.dart
+++ b/lib/src/implementations/source_of_truth_impl.dart
@@ -2,7 +2,7 @@
 
 import 'package:stock/src/source_of_truth.dart';
 
-class SourceOfTruthImpl<Key, T> implements SourceOfTruth<Key, T> {
+final class SourceOfTruthImpl<Key, T> implements SourceOfTruth<Key, T> {
   SourceOfTruthImpl(this._reader, this._writer, this._delete, this._deleteAll);
 
   final Stream<T?> Function(Key key) _reader;
@@ -23,7 +23,8 @@ class SourceOfTruthImpl<Key, T> implements SourceOfTruth<Key, T> {
   Future<void> deleteAll() async => await _deleteAll?.call();
 }
 
-class WriteWrappedSourceOfTruth<Key, T> extends CachedSourceOfTruth<Key, T> {
+final class WriteWrappedSourceOfTruth<Key, T>
+    extends CachedSourceOfTruth<Key, T> {
   WriteWrappedSourceOfTruth(this._realSourceOfTruth);
 
   final SourceOfTruth<Key, T>? _realSourceOfTruth;
diff --git a/lib/src/source_of_truth.dart b/lib/src/source_of_truth.dart
index d9374b2..9791ef2 100644
--- a/lib/src/source_of_truth.dart
+++ b/lib/src/source_of_truth.dart
@@ -37,7 +37,7 @@ import 'package:stock/src/stock_extensions.dart';
 /// local storage is needed.
 /// For this case you can use the [mapTo] and [mapToUsingMapper] extensions.
 ///
-abstract class SourceOfTruth<Key, T> {
+abstract interface class SourceOfTruth<Key, T> {
   /// Creates a source of truth that is accessed via [reader], [writer],
   /// [delete] and [deleteAll].
   ///
diff --git a/lib/src/stock.dart b/lib/src/stock.dart
index 41de66f..6d9a99c 100644
--- a/lib/src/stock.dart
+++ b/lib/src/stock.dart
@@ -14,7 +14,7 @@ import 'package:stock/src/stock_response.dart';
 /// truth. Its purpose is to eliminate the need for waiting on a network update
 /// before local modifications are available (via [Stock.stream]).
 ///
-abstract class Stock<Key, T> {
+abstract interface class Stock<Key, T> {
   /// Stock constructor
   factory Stock({
     required Fetcher<Key, T> fetcher,
diff --git a/lib/src/stock_request.dart b/lib/src/stock_request.dart
index 7a57187..dcf1359 100644
--- a/lib/src/stock_request.dart
+++ b/lib/src/stock_request.dart
@@ -10,7 +10,7 @@ import 'package:stock/src/stock.dart';
 /// If it's `false`, [Stock] will try to return the [SourceOfTruth] data, and
 /// if it doesn't exist, [Stock] will request fresh data using the [Fetcher].
 ///
-class StockRequest<Key> {
+final class StockRequest<Key> {
   /// [StockRequest] constructor
   StockRequest({
     required this.key,
diff --git a/lib/src/stock_response.dart b/lib/src/stock_response.dart
index f7fbe6f..d58afa8 100644
--- a/lib/src/stock_response.dart
+++ b/lib/src/stock_response.dart
@@ -9,7 +9,7 @@ import 'package:stock/src/stock.dart';
 /// uses this holder class to represent each response. This allows the [Stream]
 /// to keep flowing even if an error happens so that if there is an observable
 /// single source of truth, the application can keep observing it.
-class StockResponse<Output> {
+sealed class StockResponse<Output> {
   const StockResponse._(this.origin);
 
   /// Loading event dispatched by [Stock] to signal the [Fetcher] is currently
@@ -35,7 +35,7 @@ class StockResponse<Output> {
 /// Loading event dispatched by [Stock] to signal the [Fetcher] is currently
 /// running.
 @immutable
-class StockResponseLoading<T> extends StockResponse<T> {
+final class StockResponseLoading<T> extends StockResponse<T> {
   /// StockResponseLoading constructor
   const StockResponseLoading(super.origin) : super._();
 
@@ -56,7 +56,7 @@ class StockResponseLoading<T> extends StockResponse<T> {
 
 /// Data dispatched by [Stock]
 @immutable
-class StockResponseData<T> extends StockResponse<T> {
+final class StockResponseData<T> extends StockResponse<T> {
   /// StockResponseData constructor
   const StockResponseData(super.origin, this.value) : super._();
 
@@ -80,7 +80,7 @@ class StockResponseData<T> extends StockResponse<T> {
 
 /// Error dispatched by a pipeline
 @immutable
-class StockResponseError<T> extends StockResponse<T> {
+final class StockResponseError<T> extends StockResponse<T> {
   /// StockResponseError constructor
   const StockResponseError(super.origin, this.error, [this.stackTrace])
       : super._();
diff --git a/lib/src/stock_response_extensions.dart b/lib/src/stock_response_extensions.dart
index 7ab7984..24f04d9 100644
--- a/lib/src/stock_response_extensions.dart
+++ b/lib/src/stock_response_extensions.dart
@@ -5,25 +5,27 @@ import 'package:stock/src/stock_response.dart';
 /// Useful [StockResponse] extensions.
 extension StockResponseExtensions<T> on StockResponse<T> {
   /// Returns the available data or throws error if there is no data.
-  T requireData() => when(
-        onData: (_, data) => data,
-        onLoading: (_) => throw StockError('There is no data in loading'),
+  T requireData() => switch (this) {
+        StockResponseLoading<T>() =>
+          throw StockError('There is no data in loading'),
+        StockResponseData<T>(value: final value) => value,
         // ignore: only_throw_errors
-        onError: (_, error, __) => throw error,
-      );
+        StockResponseError<T>(error: final error) => throw error,
+      };
 
   /// If there is data available, returns it; otherwise returns null.
-  T? getDataOrNull() => this is StockResponseData<T>
-      ? (this as StockResponseData<T>).value
-      : null;
+  T? getDataOrNull() => switch (this) {
+        StockResponseData<T>(value: final value) => value,
+        _ => null
+      };
 
   /// Returns the available data or throws error if there is no data.
-  Object requireError() => maybeMap(
-        onError: (response) => response.error,
-        orElse: () => throw StockError(
-          'Response is not an StockResponseError. Response: $this',
-        ),
-      );
+  Object requireError() => switch (this) {
+        StockResponseError<T>(error: final error) => error,
+        _ => throw StockError(
+            'Response is not an StockResponseError. Response: $this',
+          ),
+      };
 
   /// If this [StockResponse] is of type [StockResponseError], throws the
   /// exception. Otherwise, does nothing.
@@ -61,17 +63,12 @@ extension StockResponseExtensions<T> on StockResponse<T> {
     required E Function(StockResponseLoading<T> value) onLoading,
     required E Function(StockResponseData<T> value) onData,
     required E Function(StockResponseError<T> value) onError,
-  }) {
-    if (this is StockResponseLoading<T>) {
-      return onLoading(this as StockResponseLoading<T>);
-    } else if (this is StockResponseData<T>) {
-      return onData(this as StockResponseData<T>);
-    } else if (this is StockResponseError<T>) {
-      return onError(this as StockResponseError<T>);
-    } else {
-      throw StockError('Unknown StockResponse type: $this');
-    }
-  }
+  }) =>
+      switch (this) {
+        StockResponseLoading<T>() => onLoading(this as StockResponseLoading<T>),
+        StockResponseData<T>() => onData(this as StockResponseData<T>),
+        StockResponseError<T>() => onError(this as StockResponseError<T>),
+      };
 
   /// Invokes [onData] or [orElse] as fallback if the response is successful,
   /// [onLoading] or [orElse] as fallback if the response is loading, and
diff --git a/lib/src/type_mapper.dart b/lib/src/type_mapper.dart
index 3844cfa..ca8f70e 100644
--- a/lib/src/type_mapper.dart
+++ b/lib/src/type_mapper.dart
@@ -1,6 +1,6 @@
 /// Converts the [Input] type to the [Output] and vice versa.
 /// Used to transform DB entity to network entity and vice versa.
-abstract class StockTypeMapper<Input, Output> {
+abstract interface class StockTypeMapper<Input, Output> {
   /// Transform a [Input] into a [Output]
   Output fromInput(Input value);
 
diff --git a/test/clear_and_clear_all_test.dart b/test/clear_and_clear_all_test.dart
index 7026104..6c4eccd 100644
--- a/test/clear_and_clear_all_test.dart
+++ b/test/clear_and_clear_all_test.dart
@@ -1,18 +1,20 @@
 import 'package:mockito/mockito.dart';
+import 'package:stock/src/implementations/factory_fetcher.dart';
 import 'package:stock/src/stock.dart';
 import 'package:test/test.dart';
 
+import 'common/fetcher_mock.dart';
 import 'common/source_of_truth/cached_and_mocked_source_of_truth.dart';
-import 'common_mocks.mocks.dart';
 
 void main() {
   group('Clear tests', () {
     test('Stock Clear invokes SOT clear', () async {
       final sourceOfTruth = createMockedSourceOfTruth<int, int>();
 
-      final fetcher = MockFutureFetcher<int, int>();
       var timesCalled = 0;
-      when(fetcher.factory).thenReturn((key) => Stream.value(++timesCalled));
+      final mockFetcher =
+          MockFutureFetcher<int, int>((key) => Future.value(++timesCalled));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
 
       final stock = Stock<int, int>(
         fetcher: fetcher,
@@ -28,9 +30,10 @@ void main() {
     test('Stock ClearAll invokes SOT clearAll', () async {
       final sourceOfTruth = createMockedSourceOfTruth<int, int>();
 
-      final fetcher = MockFutureFetcher<int, int>();
       var timesCalled = 0;
-      when(fetcher.factory).thenReturn((key) => Stream.value(++timesCalled));
+      final mockFetcher =
+          MockFutureFetcher<int, int>((key) => Future.value(++timesCalled));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
 
       final stock = Stock<int, int>(
         fetcher: fetcher,
diff --git a/test/common/fetcher_mock.dart b/test/common/fetcher_mock.dart
new file mode 100644
index 0000000..c805fdb
--- /dev/null
+++ b/test/common/fetcher_mock.dart
@@ -0,0 +1,12 @@
+class MockFutureFetcher<Key, Output> {
+  MockFutureFetcher(Future<Output> Function(Key key) factory) {
+    this.factory = (key) {
+      invocations++;
+      return factory(key);
+    };
+  }
+
+  int invocations = 0;
+
+  late Future<Output> Function(Key key) factory;
+}
diff --git a/test/common_mocks.dart b/test/common_mocks.dart
index 1995ff6..6c0a65b 100644
--- a/test/common_mocks.dart
+++ b/test/common_mocks.dart
@@ -1,5 +1,4 @@
 import 'package:mockito/annotations.dart';
-import 'package:stock/src/implementations/factory_fetcher.dart';
 import 'package:stock/src/source_of_truth.dart';
 
 import 'stock_response_extension_test.dart';
@@ -7,8 +6,6 @@ import 'stock_response_extension_test.dart';
 @GenerateMocks([
   CallbackVoid,
   CallbackInt,
-  FutureFetcher,
-  StreamFetcher,
   SourceOfTruth,
 ])
 void main() {}
diff --git a/test/common_mocks.mocks.dart b/test/common_mocks.mocks.dart
index ec07837..54ccc83 100644
--- a/test/common_mocks.mocks.dart
+++ b/test/common_mocks.mocks.dart
@@ -1,4 +1,4 @@
-// Mocks generated by Mockito 5.3.0 from annotations
+// Mocks generated by Mockito 5.4.2 from annotations
 // in stock/test/common_mocks.dart.
 // Do not manually edit this file.
 
@@ -6,8 +6,7 @@
 import 'dart:async' as _i4;
 
 import 'package:mockito/mockito.dart' as _i1;
-import 'package:stock/src/implementations/factory_fetcher.dart' as _i3;
-import 'package:stock/src/source_of_truth.dart' as _i5;
+import 'package:stock/src/source_of_truth.dart' as _i3;
 
 import 'stock_response_extension_test.dart' as _i2;
 
@@ -58,59 +57,11 @@ class MockCallbackInt extends _i1.Mock implements _i2.CallbackInt {
       ) as int);
 }
 
-/// A class which mocks [FutureFetcher].
-///
-/// See the documentation for Mockito's code generation for more information.
-class MockFutureFetcher<Key, Output> extends _i1.Mock
-    implements _i3.FutureFetcher<Key, Output> {
-  MockFutureFetcher() {
-    _i1.throwOnMissingStub(this);
-  }
-
-  @override
-  _i4.Stream<Output> Function(Key) get factory => (super.noSuchMethod(
-        Invocation.getter(#factory),
-        returnValue: (Key key) => _i4.Stream<Output>.empty(),
-      ) as _i4.Stream<Output> Function(Key));
-  @override
-  set factory(_i4.Stream<Output> Function(Key)? _factory) => super.noSuchMethod(
-        Invocation.setter(
-          #factory,
-          _factory,
-        ),
-        returnValueForMissingStub: null,
-      );
-}
-
-/// A class which mocks [StreamFetcher].
-///
-/// See the documentation for Mockito's code generation for more information.
-class MockStreamFetcher<Key, Output> extends _i1.Mock
-    implements _i3.StreamFetcher<Key, Output> {
-  MockStreamFetcher() {
-    _i1.throwOnMissingStub(this);
-  }
-
-  @override
-  _i4.Stream<Output> Function(Key) get factory => (super.noSuchMethod(
-        Invocation.getter(#factory),
-        returnValue: (Key key) => _i4.Stream<Output>.empty(),
-      ) as _i4.Stream<Output> Function(Key));
-  @override
-  set factory(_i4.Stream<Output> Function(Key)? _factory) => super.noSuchMethod(
-        Invocation.setter(
-          #factory,
-          _factory,
-        ),
-        returnValueForMissingStub: null,
-      );
-}
-
 /// A class which mocks [SourceOfTruth].
 ///
 /// See the documentation for Mockito's code generation for more information.
 class MockSourceOfTruth<Key, T> extends _i1.Mock
-    implements _i5.SourceOfTruth<Key, T> {
+    implements _i3.SourceOfTruth<Key, T> {
   MockSourceOfTruth() {
     _i1.throwOnMissingStub(this);
   }
@@ -123,6 +74,7 @@ class MockSourceOfTruth<Key, T> extends _i1.Mock
         ),
         returnValue: _i4.Stream<T?>.empty(),
       ) as _i4.Stream<T?>);
+
   @override
   _i4.Future<void> write(
     Key? key,
@@ -139,6 +91,7 @@ class MockSourceOfTruth<Key, T> extends _i1.Mock
         returnValue: _i4.Future<void>.value(),
         returnValueForMissingStub: _i4.Future<void>.value(),
       ) as _i4.Future<void>);
+
   @override
   _i4.Future<void> delete(Key? key) => (super.noSuchMethod(
         Invocation.method(
@@ -148,6 +101,7 @@ class MockSourceOfTruth<Key, T> extends _i1.Mock
         returnValue: _i4.Future<void>.value(),
         returnValueForMissingStub: _i4.Future<void>.value(),
       ) as _i4.Future<void>);
+
   @override
   _i4.Future<void> deleteAll() => (super.noSuchMethod(
         Invocation.method(
diff --git a/test/fresh_and_get_test.dart b/test/fresh_and_get_test.dart
index 62d0796..6e6c1ab 100644
--- a/test/fresh_and_get_test.dart
+++ b/test/fresh_and_get_test.dart
@@ -1,15 +1,16 @@
 import 'package:mockito/mockito.dart';
+import 'package:stock/src/implementations/factory_fetcher.dart';
 import 'package:stock/src/stock.dart';
 import 'package:test/test.dart';
 
+import 'common/fetcher_mock.dart';
 import 'common/source_of_truth/cached_and_mocked_source_of_truth.dart';
-import 'common_mocks.mocks.dart';
 
 void main() {
   group('Fresh tests', () {
     test('Sot is not called when fresh is invoked', () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth = createMockedSourceOfTruthFromMethods<int, int>(
         (key) => Stream.value(-1),
         (key, output) => Future.value(),
@@ -29,8 +30,8 @@ void main() {
   group('Get tests', () {
     test('Fetcher is not called when get is invoked and sot has data',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth = createMockedSourceOfTruthFromMethods<int, int>(
         (key) => Stream.value(-1),
         (key, output) => Future.value(),
@@ -42,15 +43,15 @@ void main() {
 
       final result = await stock.get(1);
       expect(result, equals(-1));
-      verifyNever(fetcher.factory);
+      expect(mockFetcher.invocations, equals(0));
       verify(sourceOfTruth.reader(any)).called(1);
       verifyNever(sourceOfTruth.write(any, any));
     });
 
     test('Fetcher is called when get is invoked and sot has not data',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mock = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mock.factory);
       final sourceOfTruth = createMockedSourceOfTruth<int, int>();
       final stock = Stock<int, int>(
         fetcher: fetcher,
@@ -59,7 +60,7 @@ void main() {
 
       final result = await stock.get(1);
       expect(result, equals(1));
-      verify(fetcher.factory).called(1);
+      expect(mock.invocations, equals(1));
       verify(sourceOfTruth.reader(any)).called(1);
       verify(sourceOfTruth.write(any, any)).called(1);
     });
diff --git a/test/refresh_test.dart b/test/refresh_test.dart
index b0a9752..a177f90 100644
--- a/test/refresh_test.dart
+++ b/test/refresh_test.dart
@@ -1,20 +1,20 @@
-import 'package:mockito/mockito.dart';
+import 'package:stock/src/implementations/factory_fetcher.dart';
 import 'package:stock/src/source_of_truth.dart';
 import 'package:stock/src/stock.dart';
 import 'package:stock/src/stock_response.dart';
 import 'package:test/test.dart';
 
+import 'common/fetcher_mock.dart';
 import 'common/source_of_truth/cached_source_of_truth_with_default_value.dart';
 import 'common/source_of_truth/source_of_truth_with_error.dart';
 import 'common/stock_test_extensions.dart';
-import 'common_mocks.mocks.dart';
 
 void main() {
   group('Refresh tests', () {
     test('Fetcher is not called if sot has data and refresh is false',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth = CachedSourceOfTruthWithDefaultValue<int, int>(-1);
       final stock = Stock<int, int>(
         fetcher: fetcher,
@@ -28,12 +28,13 @@ void main() {
           const StockResponse.data(ResponseOrigin.sourceOfTruth, -1),
         ]),
       );
-      verifyNever(fetcher.factory);
+      expect(mockFetcher.invocations, equals(0));
     });
 
     test('Fetcher is called if sot has data and refresh is true', () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
+
       final sourceOfTruth = CachedSourceOfTruthWithDefaultValue<int, int>(-1);
       final stock = Stock<int, int>(
         fetcher: fetcher,
@@ -49,13 +50,13 @@ void main() {
           const StockResponse.data(ResponseOrigin.fetcher, 1),
         ]),
       );
-      verify(fetcher.factory).called(1);
+      expect(mockFetcher.invocations, equals(1));
     });
 
     test('Fetcher is called if sot has not data and refresh is false',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth = CachedSourceOfTruth<int, int>();
       final stock = Stock<int, int>(
         fetcher: fetcher,
@@ -70,13 +71,13 @@ void main() {
           const StockResponse.data(ResponseOrigin.fetcher, 1),
         ]),
       );
-      verify(fetcher.factory).called(1);
+      expect(mockFetcher.invocations, equals(1));
     });
 
     test('Fetcher is called if sot returns an error and refresh is false',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth =
           SourceOfTruthWithError<int, int>(null, throwReadErrorCount: 1);
       final stock = Stock<int, int>(
@@ -97,13 +98,13 @@ void main() {
           const StockResponse.data(ResponseOrigin.fetcher, 1),
         ]),
       );
-      verify(fetcher.factory).called(1);
+      expect(mockFetcher.invocations, equals(1));
     });
 
     test('Fetcher is called if sot returns an error and refresh is true',
         () async {
-      final fetcher = MockFutureFetcher<int, int>();
-      when(fetcher.factory).thenReturn((key) => Stream.value(1));
+      final mockFetcher = MockFutureFetcher<int, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<int, int>(mockFetcher.factory);
       final sourceOfTruth =
           SourceOfTruthWithError<int, int>(null, throwReadErrorCount: 1);
       final stock = Stock<int, int>(
@@ -124,7 +125,7 @@ void main() {
           const StockResponse.data(ResponseOrigin.fetcher, 1),
         ]),
       );
-      verify(fetcher.factory).called(1);
+      expect(mockFetcher.invocations, equals(1));
     });
   });
 }
diff --git a/test/stock_response_extension_test.dart b/test/stock_response_extension_test.dart
index ae085bd..7cf675c 100644
--- a/test/stock_response_extension_test.dart
+++ b/test/stock_response_extension_test.dart
@@ -1,6 +1,5 @@
 import 'package:mockito/mockito.dart';
 import 'package:stock/src/errors.dart';
-import 'package:stock/src/extensions/stock_response_internal_extensions.dart';
 import 'package:stock/src/stock_response.dart';
 import 'package:stock/src/stock_response_extensions.dart';
 import 'package:test/test.dart';
@@ -155,32 +154,6 @@ void main() {
     });
   });
 
-  group('Unknown type', () {
-    test('Require data throws error if the type is not recognized', () async {
-      expect(
-        _FakeType().requireData,
-        throwsA(
-          (dynamic e) =>
-              e is StockError &&
-              e.toString().contains('Unknown StockResponse type:'),
-        ),
-      );
-    });
-
-    test('Swap type throws error if the type is not recognized', () async {
-      expect(
-        _FakeType().swapType,
-        throwsA(
-          (dynamic e) =>
-              e is StockError &&
-              e.toString().contains(
-                    "Unknown StockResponse type: Instance of '_FakeType'",
-                  ),
-        ),
-      );
-    });
-  });
-
   group('Map', () {
     test('mapData', () {
       final loading = const StockResponseLoading<int>(ResponseOrigin.fetcher)
@@ -245,29 +218,6 @@ void main() {
       verifyNever(mockDataCallback());
       verify(mockErrorCallback()).called(1);
     });
-
-    test('Map with unknown type', () async {
-      final mockLoadingCallback = MockCallbackVoid();
-      final mockDataCallback = MockCallbackVoid();
-      final mockErrorCallback = MockCallbackVoid();
-      expect(
-        () {
-          _FakeType().map(
-            onLoading: (_) => mockLoadingCallback(),
-            onData: (_) => mockDataCallback(),
-            onError: (_) => mockErrorCallback(),
-          );
-        },
-        throwsA(
-          (dynamic e) =>
-              e is StockError &&
-              e.message.startsWith('Unknown StockResponse type: '),
-        ),
-      );
-      verifyNever(mockLoadingCallback());
-      verifyNever(mockDataCallback());
-      verifyNever(mockErrorCallback());
-    });
   });
 
   group('MaybeMap', () {
@@ -680,8 +630,3 @@ abstract class Callback<T> {
 abstract class CallbackVoid implements Callback<void> {}
 
 abstract class CallbackInt implements Callback<int> {}
-
-class _FakeType implements StockResponse<int> {
-  @override
-  ResponseOrigin get origin => ResponseOrigin.fetcher;
-}
diff --git a/test/stock_without_key_test.dart b/test/stock_without_key_test.dart
index f908812..4312a8d 100644
--- a/test/stock_without_key_test.dart
+++ b/test/stock_without_key_test.dart
@@ -1,17 +1,18 @@
-import 'package:mockito/mockito.dart';
+import 'package:stock/src/implementations/factory_fetcher.dart';
 import 'package:stock/src/stock.dart';
 import 'package:stock/src/stock_response.dart';
 import 'package:test/test.dart';
 
+import 'common/fetcher_mock.dart';
 import 'common/source_of_truth/cached_source_of_truth_with_default_value.dart';
 import 'common/stock_test_extensions.dart';
-import 'common_mocks.mocks.dart';
 
 void main() {
   group('Stock without specific key', () {
     test('Simple request using dynamic', () async {
-      final fetcher = MockFutureFetcher<dynamic, int>();
-      when(fetcher.factory).thenReturn((_) => Stream.value(1));
+      final mockFetcher =
+          MockFutureFetcher<dynamic, int>((key) => Future.value(1));
+      final fetcher = FutureFetcher<dynamic, int>(mockFetcher.factory);
       final sourceOfTruth = CachedSourceOfTruthWithDefaultValue<void, int>(-1);
       final stock = Stock<dynamic, int>(
         fetcher: fetcher,