added fpdart demo

2024-11-27 15:59:08 +01:00
parent 89e12bdf9f
commit caf6007c26
10 changed files with 755 additions and 254 deletions
@@ -0,0 +1,3 @@
+# https://dart.dev/guides/libraries/private-files
+# Created by `dart pub`
+.dart_tool/
@@ -0,0 +1 @@
+none
@@ -0,0 +1,44 @@
+# **🚀 Demo-Projekt: AppError und Funktionale Programmierung mit fpdart**
+
+Dieses Demo-Projekt begleitet die Zwischenpräsentation und verdeutlicht, wie funktionale Programmierung mit Dart und der Bibliothek `fpdart` umgesetzt werden kann. Es greift die zentralen Konzepte der Präsentation auf.
+
+Das Projekt zeigt, wie durch funktionale Ansätze mit `fpdart`:
+
+- ✅ Logik deklarativ ausgedrückt wird.
+- 🛠️ Fehler elegant und strukturiert behandelt werden.
+- 🔄 Erweiterbare, wartbare und typsichere Programme entstehen.
+
+## **🔑 Zentrale Aspekte**
+
+### **1. Monaden als Datenkonstrukte**
+
+- 📦 Anwendung von **`Either`** für synchrone Fehler- und Erfolgsverarbeitung.
+- ⏳ Verwendung von **`TaskEither`** zur Kombination von Lazy Evaluation mit asynchroner Verarbeitung und Fehlerbehandlung.
+
+### **2. 🛡️ `AppError`: Einheitliche Fehlerstruktur**
+
+- Einführung eines stark typisierten `AppError`, um Fehler systematisch zu kategorisieren (z. B. `ValidationError`, `DatabaseError`, `NetworkError`).
+- Klare Trennung von:
+  - 📄 **Nachricht** (für Benutzer)
+  - ⚙️ **Typ** (zur Kategorisierung)
+  - 🔍 **Details** (für Debugging)
+
+### **3. Praxisnahe Beispiele**
+
+- 🔍 **Validierung**: Prüfung von Benutzereingaben mit `Either`.
+- 🛠️ **Fehlerbehandlung**: Nutzung von `TaskEither` für Datenbank- und Netzwerkfehler.
+- 🔗 **Verkettung von Funktionen**:
+  - Nahtlose Kombination von Validierung, Speicherung und weiteren Prozessen.
+  - Kein Abbruch bei Zwischenfehlern.
+
+### **4. Verbindung zu funktionalen Konzepten**
+
+- 🏛️ **Ursprung**: Konzepte aus Haskell und FP-TS.
+- 🌀 **Monaden**: Praktische Anwendung zur sicheren Datenverarbeitung ohne Seiteneffekte.
+- 🌐 **Anwendungsbezug**: Funktionale Programmierung als Werkzeug für robuste und skalierbare Software.
+
+Das Projekt dient als praktische Grundlage, um die in der Präsentation behandelten Konzepte von funktionaler Programmierung und Fehlerbehandlung greifbar zu machen. Es zeigt, wie mit `fpdart`:
+
+- Der Code sauber und wartbar bleibt.
+- Funktionale Programmierung in Dart effektiv umgesetzt wird.
+- Fehlermanagement nicht nur robust, sondern auch elegant sein kann.
@@ -0,0 +1,30 @@
+# This file configures the static analysis results for your project (errors,
+# warnings, and lints).
+#
+# This enables the 'recommended' set of lints from `package:lints`.
+# This set helps identify many issues that may lead to problems when running
+# or consuming Dart code, and enforces writing Dart using a single, idiomatic
+# style and format.
+#
+# If you want a smaller set of lints you can change this to specify
+# 'package:lints/core.yaml'. These are just the most critical lints
+# (the recommended set includes the core lints).
+# The core lints are also what is used by pub.dev for scoring packages.
+
+include: package:lints/recommended.yaml
+
+# Uncomment the following section to specify additional rules.
+
+# linter:
+#   rules:
+#     - camel_case_types
+
+# analyzer:
+#   exclude:
+#     - path/to/excluded/files/**
+
+# For more information about the core and recommended set of lints, see
+# https://dart.dev/go/core-lints
+
+# For additional information about configuring this file, see
+# https://dart.dev/guides/language/analysis-options
@@ -0,0 +1,46 @@
+import 'package:fpdart/fpdart.dart';
+
+// Fehlerkategorien
+enum AppErrorType {
+  ValidationError,
+  DatabaseError,
+  NetworkError,
+  UnknownError,
+}
+
+class AppError {
+  final String message; // Benutzerfreundliche Fehlermeldung
+  final AppErrorType type; // Typisierte Fehlerkategorie
+  final Exception? exception; // Originale Exception (falls vorhanden)
+
+  AppError({
+    required this.message,
+    this.type = AppErrorType.UnknownError,
+    this.exception,
+  });
+
+  @override
+  String toString() {
+    return 'AppError(message: $message, type: $type, exception: $exception)';
+  }
+
+  /// Hilfsmethode zur einfachen Erstellung eines `Left`-Werts für `Either`
+  static Either<AppError, T> left<T>(
+    String message, {
+    AppErrorType? type,
+    Exception? exception,
+  }) {
+    return Either.left(AppError(
+      message: message,
+      type: type ?? AppErrorType.UnknownError,
+      exception: exception,
+    ));
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+
+    return other is AppError && other.message == message && other.type == type;
+  }
+}
@@ -0,0 +1,68 @@
+import 'package:demo/app_error.dart';
+import 'package:fpdart/fpdart.dart';
+
+// Mock-Datenbank
+final existingEmails = ["existing@example.com"];
+
+// Validierungsfunktionen
+Either<AppError, String> validateName(String name) {
+  return name.isNotEmpty
+      ? Either.right(name)
+      : AppError.left(
+          "Name cannot be empty",
+          type: AppErrorType.ValidationError,
+        );
+}
+
+Either<AppError, String> validateEmail(String email) {
+  final emailRegex = RegExp(r"^[a-zA-Z0-9.]+@[a-zA-Z0-9]+\.[a-zA-Z]+");
+  return emailRegex.hasMatch(email)
+      ? Either.right(email)
+      : AppError.left(
+          "Invalid email format",
+          type: AppErrorType.ValidationError,
+        );
+}
+
+// Asynchrone Überprüfung, ob die E-Mail bereits existiert
+TaskEither<AppError, bool> checkEmailExists(String email) {
+  return TaskEither.tryCatch(
+    () async => existingEmails.contains(email),
+    (error, _) => AppError(
+      message: "Error checking email existence",
+      type: AppErrorType.DatabaseError,
+      exception: error as Exception?,
+    ),
+  );
+}
+
+// Benutzer in der Datenbank speichern (Dummy-Implementierung)
+TaskEither<AppError, bool> saveUser(String name, String email) {
+  return TaskEither.tryCatch(
+    () async {
+      await Future.delayed(Duration(seconds: 1)); // Simulierte Latenz
+      print("User saved: $name, $email");
+      return true;
+    },
+    (error, _) => AppError(
+      message: "Error saving user",
+      type: AppErrorType.DatabaseError,
+      exception: error as Exception?,
+    ),
+  );
+}
+
+// Optional: Begrüßungsnachricht senden
+TaskEither<AppError, bool> sendWelcomeEmail(String email) {
+  return TaskEither.tryCatch(
+    () async {
+      print("Welcome email sent to $email");
+      return true;
+    },
+    (error, _) => AppError(
+      message: "Error sending welcome email",
+      type: AppErrorType.NetworkError,
+      exception: error as Exception?,
+    ),
+  );
+}
@@ -0,0 +1,410 @@
+# Generated by pub
+# See https://dart.dev/tools/pub/glossary#lockfile
+packages:
+  _fe_analyzer_shared:
+    dependency: transitive
+    description:
+      name: _fe_analyzer_shared
+      sha256: "45cfa8471b89fb6643fe9bf51bd7931a76b8f5ec2d65de4fb176dba8d4f22c77"
+      url: "https://pub.dev"
+    source: hosted
+    version: "73.0.0"
+  _macros:
+    dependency: transitive
+    description: dart
+    source: sdk
+    version: "0.3.2"
+  analyzer:
+    dependency: transitive
+    description:
+      name: analyzer
+      sha256: "4959fec185fe70cce007c57e9ab6983101dbe593d2bf8bbfb4453aaec0cf470a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.8.0"
+  args:
+    dependency: transitive
+    description:
+      name: args
+      sha256: bf9f5caeea8d8fe6721a9c358dd8a5c1947b27f1cfaa18b39c301273594919e6
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.6.0"
+  async:
+    dependency: transitive
+    description:
+      name: async
+      sha256: d2872f9c19731c2e5f10444b14686eb7cc85c76274bd6c16e1816bff9a3bab63
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.12.0"
+  boolean_selector:
+    dependency: transitive
+    description:
+      name: boolean_selector
+      sha256: "8aab1771e1243a5063b8b0ff68042d67334e3feab9e95b9490f9a6ebf73b42ea"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  collection:
+    dependency: transitive
+    description:
+      name: collection
+      sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.19.1"
+  convert:
+    dependency: transitive
+    description:
+      name: convert
+      sha256: b30acd5944035672bc15c6b7a8b47d773e41e2f17de064350988c5d02adb1c68
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.2"
+  coverage:
+    dependency: transitive
+    description:
+      name: coverage
+      sha256: "4b03e11f6d5b8f6e5bb5e9f7889a56fe6c5cbe942da5378ea4d4d7f73ef9dfe5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.11.0"
+  crypto:
+    dependency: transitive
+    description:
+      name: crypto
+      sha256: "1e445881f28f22d6140f181e07737b22f1e099a5e1ff94b0af2f9e4a463f4855"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.6"
+  file:
+    dependency: transitive
+    description:
+      name: file
+      sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.0.1"
+  fpdart:
+    dependency: "direct main"
+    description:
+      name: fpdart
+      sha256: "1b84ce64453974159f08046f5d05592020d1fcb2099d7fe6ec58da0e7337af77"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
+  frontend_server_client:
+    dependency: transitive
+    description:
+      name: frontend_server_client
+      sha256: f64a0333a82f30b0cca061bc3d143813a486dc086b574bfb233b7c1372427694
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.0.0"
+  glob:
+    dependency: transitive
+    description:
+      name: glob
+      sha256: "0e7014b3b7d4dac1ca4d6114f82bf1782ee86745b9b42a92c9289c23d8a0ab63"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  http_multi_server:
+    dependency: transitive
+    description:
+      name: http_multi_server
+      sha256: "97486f20f9c2f7be8f514851703d0119c3596d14ea63227af6f7a481ef2b2f8b"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.1"
+  http_parser:
+    dependency: transitive
+    description:
+      name: http_parser
+      sha256: "76d306a1c3afb33fe82e2bbacad62a61f409b5634c915fceb0d799de1a913360"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.1.1"
+  io:
+    dependency: transitive
+    description:
+      name: io
+      sha256: "2ec25704aba361659e10e3e5f5d672068d332fc8ac516421d483a11e5cbd061e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.4"
+  js:
+    dependency: transitive
+    description:
+      name: js
+      sha256: c1b2e9b5ea78c45e1a0788d29606ba27dc5f71f019f32ca5140f61ef071838cf
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.1"
+  lints:
+    dependency: "direct dev"
+    description:
+      name: lints
+      sha256: "976c774dd944a42e83e2467f4cc670daef7eed6295b10b36ae8c85bcbf828235"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.0.0"
+  logging:
+    dependency: transitive
+    description:
+      name: logging
+      sha256: c8245ada5f1717ed44271ed1c26b8ce85ca3228fd2ffdb75468ab01979309d61
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.0"
+  macros:
+    dependency: transitive
+    description:
+      name: macros
+      sha256: "0acaed5d6b7eab89f63350bccd82119e6c602df0f391260d0e32b5e23db79536"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.2-main.4"
+  matcher:
+    dependency: transitive
+    description:
+      name: matcher
+      sha256: d2323aa2060500f906aa31a895b4030b6da3ebdcc5619d14ce1aada65cd161cb
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.12.16+1"
+  meta:
+    dependency: transitive
+    description:
+      name: meta
+      sha256: e3641ec5d63ebf0d9b41bd43201a66e3fc79a65db5f61fc181f04cd27aab950c
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.16.0"
+  mime:
+    dependency: transitive
+    description:
+      name: mime
+      sha256: "41a20518f0cb1256669420fdba0cd90d21561e560ac240f26ef8322e45bb7ed6"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.0"
+  node_preamble:
+    dependency: transitive
+    description:
+      name: node_preamble
+      sha256: "6e7eac89047ab8a8d26cf16127b5ed26de65209847630400f9aefd7cd5c730db"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.2"
+  package_config:
+    dependency: transitive
+    description:
+      name: package_config
+      sha256: "1c5b77ccc91e4823a5af61ee74e6b972db1ef98c2ff5a18d3161c982a55448bd"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.0"
+  path:
+    dependency: transitive
+    description:
+      name: path
+      sha256: "75cca69d1490965be98c73ceaea117e8a04dd21217b37b292c9ddbec0d955bc5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.9.1"
+  pool:
+    dependency: transitive
+    description:
+      name: pool
+      sha256: "20fe868b6314b322ea036ba325e6fc0711a22948856475e2c2b6306e8ab39c2a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.5.1"
+  pub_semver:
+    dependency: transitive
+    description:
+      name: pub_semver
+      sha256: "40d3ab1bbd474c4c2328c91e3a7df8c6dd629b79ece4c4bd04bee496a224fb0c"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.4"
+  shelf:
+    dependency: transitive
+    description:
+      name: shelf
+      sha256: e7dd780a7ffb623c57850b33f43309312fc863fb6aa3d276a754bb299839ef12
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.2"
+  shelf_packages_handler:
+    dependency: transitive
+    description:
+      name: shelf_packages_handler
+      sha256: "89f967eca29607c933ba9571d838be31d67f53f6e4ee15147d5dc2934fee1b1e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.2"
+  shelf_static:
+    dependency: transitive
+    description:
+      name: shelf_static
+      sha256: c87c3875f91262785dade62d135760c2c69cb217ac759485334c5857ad89f6e3
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.3"
+  shelf_web_socket:
+    dependency: transitive
+    description:
+      name: shelf_web_socket
+      sha256: cc36c297b52866d203dbf9332263c94becc2fe0ceaa9681d07b6ef9807023b67
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.1"
+  source_map_stack_trace:
+    dependency: transitive
+    description:
+      name: source_map_stack_trace
+      sha256: c0713a43e323c3302c2abe2a1cc89aa057a387101ebd280371d6a6c9fa68516b
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  source_maps:
+    dependency: transitive
+    description:
+      name: source_maps
+      sha256: "708b3f6b97248e5781f493b765c3337db11c5d2c81c3094f10904bfa8004c703"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.10.12"
+  source_span:
+    dependency: transitive
+    description:
+      name: source_span
+      sha256: "53e943d4206a5e30df338fd4c6e7a077e02254531b138a15aec3bd143c1a8b3c"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.10.0"
+  stack_trace:
+    dependency: transitive
+    description:
+      name: stack_trace
+      sha256: "9f47fd3630d76be3ab26f0ee06d213679aa425996925ff3feffdec504931c377"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.12.0"
+  stream_channel:
+    dependency: transitive
+    description:
+      name: stream_channel
+      sha256: ba2aa5d8cc609d96bbb2899c28934f9e1af5cddbd60a827822ea467161eb54e7
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  string_scanner:
+    dependency: transitive
+    description:
+      name: string_scanner
+      sha256: "0bd04f5bb74fcd6ff0606a888a30e917af9bd52820b178eaa464beb11dca84b6"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.0"
+  term_glyph:
+    dependency: transitive
+    description:
+      name: term_glyph
+      sha256: a29248a84fbb7c79282b40b8c72a1209db169a2e0542bce341da992fe1bc7e84
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.1"
+  test:
+    dependency: "direct dev"
+    description:
+      name: test
+      sha256: f2a018e2baa6fce7c8daa55b8bdf4b3d7d165f82caac269e4cbe5edd666c0e4c
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.25.9"
+  test_api:
+    dependency: transitive
+    description:
+      name: test_api
+      sha256: fb31f383e2ee25fbbfe06b40fe21e1e458d14080e3c67e7ba0acfde4df4e0bbd
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.4"
+  test_core:
+    dependency: transitive
+    description:
+      name: test_core
+      sha256: "60ff490bb383858015df7b7a0d883301a426edf9033989f55f091d91efb9dfaf"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.6.6"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      sha256: f9049c039ebfeb4cf7a7104a675823cd72dba8297f264b6637062516699fa006
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.0"
+  vm_service:
+    dependency: transitive
+    description:
+      name: vm_service
+      sha256: "0968250880a6c5fe7edc067ed0a13d4bae1577fe2771dcf3010d52c4a9d3ca14"
+      url: "https://pub.dev"
+    source: hosted
+    version: "14.3.1"
+  watcher:
+    dependency: transitive
+    description:
+      name: watcher
+      sha256: "3d2ad6751b3c16cf07c7fca317a1413b3f26530319181b37e3b9039b84fc01d8"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.0"
+  web:
+    dependency: transitive
+    description:
+      name: web
+      sha256: cd3543bd5798f6ad290ea73d210f423502e71900302dde696f8bff84bf89a1cb
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.0"
+  web_socket:
+    dependency: transitive
+    description:
+      name: web_socket
+      sha256: "3c12d96c0c9a4eec095246debcea7b86c0324f22df69893d538fcc6f1b8cce83"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.6"
+  web_socket_channel:
+    dependency: transitive
+    description:
+      name: web_socket_channel
+      sha256: "9f187088ed104edd8662ca07af4b124465893caf063ba29758f97af57e61da8f"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.1"
+  webkit_inspection_protocol:
+    dependency: transitive
+    description:
+      name: webkit_inspection_protocol
+      sha256: "87d3f2333bb240704cd3f1c6b5b7acd8a10e7f0bc28c28dcf14e782014f4a572"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.1"
+  yaml:
+    dependency: transitive
+    description:
+      name: yaml
+      sha256: "75769501ea3489fca56601ff33454fe45507ea3bfb014161abc3b43ae25989d5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.2"
+sdks:
+  dart: ">=3.5.4 <4.0.0"
@@ -0,0 +1,16 @@
+name: demo
+description: A sample command-line application.
+version: 1.0.0
+# repository: https://github.com/my_org/my_repo
+
+environment:
+  sdk: ^3.5.4
+
+# Add regular dependencies here.
+dependencies:
+  fpdart: ^1.1.1
+  # path: ^1.8.0
+
+dev_dependencies:
+  lints: ^4.0.0
+  test: ^1.24.0
@@ -0,0 +1,137 @@
+import 'package:demo/app_error.dart';
+import 'package:demo/demo.dart';
+import 'package:fpdart/fpdart.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group("User Registration Tests", () {
+    test("Valid name and email results in successful registration", () async {
+      final name = "John Doe";
+      final email = "newuser@example.com";
+
+      final result =
+          await Either<AppError, (String, String)>.right((name, email))
+              .flatMap((userData) => validateName(userData.$1).flatMap(
+                  (validName) => validateEmail(userData.$2)
+                      .map((validEmail) => (validName, validEmail))))
+              .toTaskEither()
+              .flatMap((validUser) => checkEmailExists(validUser.$2).flatMap(
+                  (exists) => exists
+                      ? AppError.left("Email already exists",
+                              type: AppErrorType.ValidationError)
+                          .toTaskEither()
+                      : saveUser(validUser.$1, validUser.$2)))
+              .flatMap((_) => sendWelcomeEmail(email))
+              .run();
+
+      result.match(
+        (error) => fail("Test failed with error: ${error.message}"),
+        (success) => expect(success, equals(true)),
+      );
+    });
+
+    test("Invalid email format returns validation error", () async {
+      final name = "John Doe";
+      final email = "invalid-email";
+
+      final result =
+          await Either<AppError, (String, String)>.right((name, email))
+              .flatMap((userData) => validateName(userData.$1).flatMap(
+                  (validName) => validateEmail(userData.$2)
+                      .map((validEmail) => (validName, validEmail))))
+              .toTaskEither()
+              .run();
+
+      result.match(
+        (error) {
+          expect(error.message, equals("Invalid email format"));
+          expect(error.type, equals(AppErrorType.ValidationError));
+        },
+        (success) => fail("Test succeeded unexpectedly"),
+      );
+    });
+
+    test("Existing email results in error", () async {
+      final name = "John Doe";
+      final email = "existing@example.com";
+
+      final result =
+          await Either<AppError, (String, String)>.right((name, email))
+              .flatMap((userData) => validateName(userData.$1).flatMap(
+                  (validName) => validateEmail(userData.$2)
+                      .map((validEmail) => (validName, validEmail))))
+              .toTaskEither()
+              .flatMap((validUser) => checkEmailExists(validUser.$2).flatMap(
+                  (exists) => exists
+                      ? AppError.left("Email already exists",
+                              type: AppErrorType.ValidationError)
+                          .toTaskEither()
+                      : saveUser(validUser.$1, validUser.$2)))
+              .run();
+
+      result.match(
+        (error) => expect(error.message, equals("Email already exists")),
+        (success) => fail("Test succeeded unexpectedly"),
+      );
+    });
+
+    test("Empty name returns validation error", () async {
+      final name = "";
+      final email = "newuser@example.com";
+
+      final result =
+          await Either<AppError, (String, String)>.right((name, email))
+              .flatMap((userData) => validateName(userData.$1).flatMap(
+                  (validName) => validateEmail(userData.$2)
+                      .map((validEmail) => (validName, validEmail))))
+              .toTaskEither()
+              .run();
+
+      result.match(
+        (error) => expect(
+            error,
+            equals(AppError(
+                message: "Name cannot be empty",
+                type: AppErrorType.ValidationError))),
+        (success) => fail("Test succeeded unexpectedly"),
+      );
+    });
+
+    test("Error while sending welcome email is handled gracefully", () async {
+      final name = "John Doe";
+      final email = "newuser@example.com";
+
+      // Simuliere einen Fehler beim Senden der Begrüßungs-E-Mail
+      TaskEither<AppError, bool> sendWelcomeEmail(String email) {
+        return TaskEither.left(AppError(
+          message: "Error sending welcome email",
+          type: AppErrorType.NetworkError,
+        ));
+      }
+
+      final result =
+          await Either<AppError, (String, String)>.right((name, email))
+              .flatMap((userData) => validateName(userData.$1).flatMap(
+                  (validName) => validateEmail(userData.$2)
+                      .map((validEmail) => (validName, validEmail))))
+              .toTaskEither()
+              .flatMap((validUser) =>
+                  checkEmailExists(validUser.$2).flatMap((exists) => exists
+                      ? AppError.left(
+                          "Email already exists",
+                          type: AppErrorType.ValidationError,
+                        ).toTaskEither()
+                      : saveUser(validUser.$1, validUser.$2)))
+              .flatMap((_) => sendWelcomeEmail(email))
+              .run();
+
+      result.match(
+        (error) {
+          expect(error.message, equals("Error sending welcome email"));
+          expect(error.type, equals(AppErrorType.NetworkError));
+        },
+        (success) => fail("Test succeeded unexpectedly"),
+      );
+    });
+  });
+}