Improve error handling logic in TurnierplanClient

src/Turnierplan.Adapter.Test.Functional/TurnierplanAdapterTest.cs

@@ -330,11 +330,11 @@ public async Task Turnierplan_Client_Throws_Exception_When_Version_Does_Not_Matc
         using var httpClient = new HttpClient(new MockHttpMessageHandler(_ =>
         {
             var response = new HttpResponseMessage();
-            response.StatusCode = HttpStatusCode.Unauthorized;
+            response.StatusCode = HttpStatusCode.OK;
 
             if (sendHeader)
             {
-                response.Headers.Add("x-turnierplan-version", "2024.0.0"); // old version that does not exist
+                response.Headers.Add("X-Turnierplan-Version", "2024.0.0"); // old version that does not exist
             }
 
             return response;

src/Turnierplan.Adapter/TurnierplanClient.cs

@@ -76,6 +76,7 @@ public async Task<Tournament> GetTournament(string tournamentId)
         var request = new HttpRequestMessage(HttpMethod.Get, $"/api/tournaments/{tournamentId}");
         var response = await _httpClient.SendAsync(request).ConfigureAwait(false);
 
+        EnsureSuccessResponse(response);
         VerifyServerVersion(response);
 
         return await Deserialize<Tournament>(response).ConfigureAwait(false);
@@ -99,6 +100,7 @@ public async Task<List<TournamentHeader>> GetTournaments(string folderId)
         var request = new HttpRequestMessage(HttpMethod.Get, $"/api/tournaments{query}");
         var response = await _httpClient.SendAsync(request).ConfigureAwait(false);
 
+        EnsureSuccessResponse(response);
         VerifyServerVersion(response);
 
         return await Deserialize<List<TournamentHeader>>(response).ConfigureAwait(false);
@@ -153,13 +155,16 @@ private static void VerifyServerVersion(HttpResponseMessage response)
         }
     }
 
-    private static async Task<T> Deserialize<T>(HttpResponseMessage response)
+    private static void EnsureSuccessResponse(HttpResponseMessage response)
     {
         if (response.StatusCode != HttpStatusCode.OK)
         {
             throw new TurnierplanClientException($"API returned unexpected status code: {response.StatusCode}");
         }
+    }
 
+    private static async Task<T> Deserialize<T>(HttpResponseMessage response)
+    {
         var data = await response.Content.ReadFromJsonAsync<T>(__serializerOptions).ConfigureAwait(false);
 
         return data ?? throw new TurnierplanClientException($"Failed to deserialize API response of type '{typeof(T).Name}'.");