Fixes issue with mocking (#1198)

Author: waldekmastykarz

dev-proxy-abstractions/MockResponse.cs

@@ -2,12 +2,20 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Text.Json;
+
 namespace DevProxy.Abstractions;
 
-public class MockResponse
+public class MockResponse: ICloneable
 {
     public MockResponseRequest? Request { get; set; }
     public MockResponseResponse? Response { get; set; }
+
+    public object Clone()
+    {
+        var json = JsonSerializer.Serialize(this);
+        return JsonSerializer.Deserialize<MockResponse>(json) ?? new MockResponse();
+    }
 }
 
 public class MockResponseRequest

dev-proxy-plugins/Mocks/MockResponsePlugin.cs

@@ -177,7 +177,10 @@ protected virtual Task OnRequestAsync(object? sender, ProxyRequestArgs e)
         var matchingResponse = GetMatchingMockResponse(request);
         if (matchingResponse is not null)
         {
-            ProcessMockResponseInternal(e, matchingResponse);
+            // we need to clone the response so that we're not modifying
+            // the original that might be used in other requests
+            var clonedResponse = (MockResponse)matchingResponse.Clone();
+            ProcessMockResponseInternal(e, clonedResponse);
             state.HasBeenSet = true;
             return Task.CompletedTask;
         }