diff --git a/lib/src/request/request_manager.dart b/lib/src/request/request_manager.dart
index 363a51e..de48fcf 100644
--- a/lib/src/request/request_manager.dart
+++ b/lib/src/request/request_manager.dart
@@ -89,6 +89,11 @@ class RequestManager {
 }
 
 extension RequestManagerExtensions on RequestManager {
+  /// Registers the given [handler].
+  ///
+  /// This will create a function based request handler.
+  ///
+  /// See [RequestHandler.function].
   void registerFunction<TResponse, TRequest extends Request<TResponse>>(
     FutureOr<TResponse> Function(TRequest) handler,
   ) {
diff --git a/test/unit/event/event_subscription_builder/event_subscription_builder_test.dart b/test/unit/event/event_subscription_builder/event_subscription_builder_test.dart
index 975541b..f0ea21b 100644
--- a/test/unit/event/event_subscription_builder/event_subscription_builder_test.dart
+++ b/test/unit/event/event_subscription_builder/event_subscription_builder_test.dart
@@ -26,6 +26,15 @@ void main() {
     });
 
     group('subscribe', () {
+      test('it subscribes the handler', () {
+        final handler = EventHandler<int>.function((event) {});
+
+        EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+            .subscribe(handler);
+
+        verify(() => mockEventHandlerStore.register(handler));
+      });
+
       test('it return a subscription', () {
         final subscription =
             EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
@@ -52,6 +61,13 @@ void main() {
     });
 
     group('subscribeFunction', () {
+      test('it subscribes the handler', () {
+        EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+            .subscribeFunction((event) {});
+
+        verify(() => mockEventHandlerStore.register(any<EventHandler<int>>()));
+      });
+
       test('it return a subscription', () {
         final subscription =
             EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
@@ -63,6 +79,52 @@ void main() {
           reason: 'it should return a subscription',
         );
       });
+
+      test('it can cancel the subscription', () {
+        final subscription =
+            EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+                .subscribeFunction((event) {});
+
+        subscription.cancel();
+
+        verify(
+          () => mockEventHandlerStore.unregister(any<EventHandler<int>>()),
+        );
+      });
+    });
+
+    group('subscribeFactory', () {
+      EventHandler<int> handlerFactory() =>
+          EventHandler<int>.function((event) {});
+
+      test('it subscribes the handler', () {
+        EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+            .subscribeFactory(handlerFactory);
+
+        verify(() => mockEventHandlerStore.registerFactory(handlerFactory));
+      });
+
+      test('it return a subscription', () {
+        final subscription =
+            EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+                .subscribeFactory(handlerFactory);
+
+        expect(
+          subscription,
+          isA<EventSubscription>(),
+          reason: 'it should return a subscription',
+        );
+      });
+
+      test('it can cancel the subscription', () {
+        final subscription =
+            EventSubscriptionBuilder<int>.create(mockEventHandlerStore)
+                .subscribeFactory(handlerFactory);
+
+        subscription.cancel();
+
+        verify(() => mockEventHandlerStore.unregisterFactory(handlerFactory));
+      });
     });
   });
 }
diff --git a/test/unit/request/request_handler/request_handler_store_test.dart b/test/unit/request/request_handler/request_handler_store_test.dart
index 7791f00..ecf7cc1 100644
--- a/test/unit/request/request_handler/request_handler_store_test.dart
+++ b/test/unit/request/request_handler/request_handler_store_test.dart
@@ -1,3 +1,4 @@
+import 'package:dart_mediator/src/request/handler/request_handler.dart';
 import 'package:dart_mediator/src/request/handler/request_handler_store.dart';
 import 'package:test/test.dart';
 
@@ -7,13 +8,16 @@ void main() {
   group('RequestHandlerStore', () {
     late RequestHandlerStore requestHandlerStore;
 
+    RequestHandler<int, MockRequest<int>> handlerFactory() =>
+        MockRequestHandler<int, MockRequest<int>>();
+
+    final mockRequestHandler = MockRequestHandler<int, MockRequest<int>>();
+
     setUp(() {
       requestHandlerStore = RequestHandlerStore();
     });
 
     group('register', () {
-      final mockRequestHandler = MockRequestHandler<int, MockRequest<int>>();
-
       test('it registers the handler', () {
         expect(
           () => requestHandlerStore.register(mockRequestHandler),
@@ -28,17 +32,42 @@ void main() {
           throwsAssertionError,
         );
       });
+
+      test('it throws when a factory for this type was already registered', () {
+        requestHandlerStore.registerFactory(handlerFactory);
+
+        expect(
+          () => requestHandlerStore.register(mockRequestHandler),
+          throwsAssertionError,
+        );
+      });
     });
 
     group('registerFactory', () {
       test('it registers the handler', () {
         expect(
-          () => requestHandlerStore.registerFactory<int, MockRequest<int>>(
-            () => MockRequestHandler<int, MockRequest<int>>(),
-          ),
+          () => requestHandlerStore.registerFactory(handlerFactory),
           returnsNormally,
         );
       });
+
+      test('it throws when registering the same factory multiple times', () {
+        requestHandlerStore.registerFactory(handlerFactory);
+
+        expect(
+          () => requestHandlerStore.registerFactory(handlerFactory),
+          throwsAssertionError,
+        );
+      });
+
+      test('it throws when a handler for this type was already registered', () {
+        requestHandlerStore.register(mockRequestHandler);
+
+        expect(
+          () => requestHandlerStore.registerFactory(handlerFactory),
+          throwsAssertionError,
+        );
+      });
     });
 
     group('unregister', () {
diff --git a/test/unit/request/request_handler/request_handler_test.dart b/test/unit/request/request_handler/request_handler_test.dart
new file mode 100644
index 0000000..a9fb126
--- /dev/null
+++ b/test/unit/request/request_handler/request_handler_test.dart
@@ -0,0 +1,24 @@
+import 'package:dart_mediator/src/request/handler/request_handler.dart';
+import 'package:test/test.dart';
+
+import '../../../mocks.dart';
+
+void main() {
+  group('RequestHandler', () {
+    setUp(() {});
+
+    group('handle', () {
+      test('it handles the request', () {
+        var handled = false;
+        final mockRequest = MockRequest<int>();
+        final handler = RequestHandler<int, MockRequest<int>>.function((req) {
+          handled = true;
+          return 123;
+        });
+
+        expect(handler.handle(mockRequest), 123);
+        expect(handled, isTrue);
+      });
+    });
+  });
+}