diff --git a/CHANGELOG.md b/CHANGELOG.md
index ec8a8515..6c4afbe4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,10 @@
+# 1.20.0 (24 December 2025)
+- [#1399](https://github.com/wiremock/WireMock.Net/pull/1399) - Upgrade RamlToOpenApiConverter and YamlDotNet [feature] contributed by [StefH](https://github.com/StefH)
+- [#1400](https://github.com/wiremock/WireMock.Net/pull/1400) - Add WireMock.Net.NUnit project [feature] contributed by [StefH](https://github.com/StefH)
+- [#1405](https://github.com/wiremock/WireMock.Net/pull/1405) - Fix Testcontainers AddProtoDefinition [bug] contributed by [StefH](https://github.com/StefH)
+- [#1398](https://github.com/wiremock/WireMock.Net/issues/1398) - Upgrade YamlDotNet dependency [feature]
+- [#1404](https://github.com/wiremock/WireMock.Net/issues/1404) - An exception occurs when adding multiple proto definitions in the TestContainer. [bug]
+
 # 1.19.0 (12 December 2025)
 - [#1391](https://github.com/wiremock/WireMock.Net/pull/1391) - Update WireMockContainerBuilder (WithImage and WithCustomImage) [feature] contributed by [StefH](https://github.com/StefH)
 - [#1392](https://github.com/wiremock/WireMock.Net/pull/1392) - WireMockContainerBuilder: allow all docker images named wiremock [feature] contributed by [StefH](https://github.com/StefH)
diff --git a/Directory.Build.props b/Directory.Build.props
index 6d59e440..daf48040 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -4,7 +4,7 @@
     </PropertyGroup>
 
     <PropertyGroup>
-        <VersionPrefix>1.19.0</VersionPrefix>
+        <VersionPrefix>1.20.0</VersionPrefix>
         <PackageIcon>WireMock.Net-Logo.png</PackageIcon>
         <PackageProjectUrl>https://github.com/wiremock/WireMock.Net</PackageProjectUrl>
         <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
diff --git a/Generate-ReleaseNotes.cmd b/Generate-ReleaseNotes.cmd
index dee29e49..5a5e664b 100644
--- a/Generate-ReleaseNotes.cmd
+++ b/Generate-ReleaseNotes.cmd
@@ -1,6 +1,6 @@
 rem https://github.com/StefH/GitHubReleaseNotes
 
-SET version=1.19.0
+SET version=1.20.0
 
 GitHubReleaseNotes --output CHANGELOG.md --skip-empty-releases --exclude-labels wontfix test question invalid doc duplicate example environment --version %version% --token %GH_TOKEN%
 
diff --git a/PackageReleaseNotes.txt b/PackageReleaseNotes.txt
index 1cc929a6..d0d374b0 100644
--- a/PackageReleaseNotes.txt
+++ b/PackageReleaseNotes.txt
@@ -1,6 +1,8 @@
-# 1.19.0 (12 December 2025)
-- #1391 Update WireMockContainerBuilder (WithImage and WithCustomImage) [feature]
-- #1392 WireMockContainerBuilder: allow all docker images named wiremock [feature]
-- #1390 Unable to build WireMockContainerBuilder with custom image [feature]
+# 1.20.0 (24 December 2025)
+- #1399 Upgrade RamlToOpenApiConverter and YamlDotNet [feature]
+- #1400 Add WireMock.Net.NUnit project [feature]
+- #1405 Fix Testcontainers AddProtoDefinition [bug]
+- #1398 Upgrade YamlDotNet dependency [feature]
+- #1404 An exception occurs when adding multiple proto definitions in the TestContainer. [bug]
 
 The full release notes can be found here: https://github.com/wiremock/WireMock.Net/blob/master/CHANGELOG.md
\ No newline at end of file
diff --git a/src/WireMock.Net.ProtoBuf/Matchers/ProtoBufMatcher.cs b/src/WireMock.Net.ProtoBuf/Matchers/ProtoBufMatcher.cs
index bbba63f3..7f79d896 100644
--- a/src/WireMock.Net.ProtoBuf/Matchers/ProtoBufMatcher.cs
+++ b/src/WireMock.Net.ProtoBuf/Matchers/ProtoBufMatcher.cs
@@ -96,14 +96,14 @@ public class ProtoBufMatcher : IProtoBufMatcher
         }
 
         var protoDefinitions = ProtoDefinition().Texts;
-       
+
         var resolver = new WireMockProtoFileResolver(protoDefinitions);
         var request = new ConvertToObjectRequest(protoDefinitions[0], MessageType, input)
             .WithProtoFileResolver(resolver);
 
         try
         {
-            return await ProtoBufToJsonConverter.ConvertAsync(request, cancellationToken).ConfigureAwait(false);
+            return await ProtoBufToJsonConverter.ConvertAsync(request, cancellationToken);
         }
         catch
         {
diff --git a/src/WireMock.Net.ProtoBuf/WireMock.Net.ProtoBuf.csproj b/src/WireMock.Net.ProtoBuf/WireMock.Net.ProtoBuf.csproj
index 47710e3d..52d1e3b0 100644
--- a/src/WireMock.Net.ProtoBuf/WireMock.Net.ProtoBuf.csproj
+++ b/src/WireMock.Net.ProtoBuf/WireMock.Net.ProtoBuf.csproj
@@ -27,7 +27,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="ProtoBufJsonConverter" Version="0.10.0.1" />
+        <PackageReference Include="ProtoBufJsonConverter" Version="0.11.0" />
     </ItemGroup>
 
     <ItemGroup>
diff --git a/src/WireMock.Net.Testcontainers/Extensions/HttpWaitStrategyExtensions.cs b/src/WireMock.Net.Testcontainers/Extensions/HttpWaitStrategyExtensions.cs
new file mode 100644
index 00000000..33aab29a
--- /dev/null
+++ b/src/WireMock.Net.Testcontainers/Extensions/HttpWaitStrategyExtensions.cs
@@ -0,0 +1,18 @@
+// Copyright © WireMock.Net
+
+using WireMock.Net.Testcontainers;
+
+namespace DotNet.Testcontainers.Configurations;
+
+internal static class HttpWaitStrategyExtensions
+{
+    internal static HttpWaitStrategy WithBasicAuthentication(this HttpWaitStrategy strategy, WireMockConfiguration configuration)
+    {
+        if (configuration.HasBasicAuthentication)
+        {
+            return strategy.WithBasicAuthentication(configuration.Username, configuration.Password);
+        }
+
+        return strategy;
+    }
+}
\ No newline at end of file
diff --git a/src/WireMock.Net.Testcontainers/Utils/CombineUtils.cs b/src/WireMock.Net.Testcontainers/Utils/CombineUtils.cs
new file mode 100644
index 00000000..caab4c75
--- /dev/null
+++ b/src/WireMock.Net.Testcontainers/Utils/CombineUtils.cs
@@ -0,0 +1,20 @@
+// Copyright © WireMock.Net
+
+using System.Collections.Generic;
+using System.Linq;
+
+namespace WireMock.Net.Testcontainers.Utils;
+
+internal static class CombineUtils
+{
+    internal static List<T> Combine<T>(List<T> oldValue, List<T> newValue)
+    {
+        return oldValue.Union(newValue).ToList();
+    }
+
+    internal static Dictionary<TKey, TValue> Combine<TKey, TValue>(Dictionary<TKey, TValue> oldValue, Dictionary<TKey, TValue> newValue)
+        where TKey : notnull
+    {
+        return oldValue.Union(newValue).ToDictionary(item => item.Key, item => item.Value);
+    }
+}
\ No newline at end of file
diff --git a/src/WireMock.Net.Testcontainers/WireMockConfiguration.cs b/src/WireMock.Net.Testcontainers/WireMockConfiguration.cs
index f7260670..dded4876 100644
--- a/src/WireMock.Net.Testcontainers/WireMockConfiguration.cs
+++ b/src/WireMock.Net.Testcontainers/WireMockConfiguration.cs
@@ -1,12 +1,12 @@
 // Copyright © WireMock.Net
 
 using System.Collections.Generic;
-using System.Linq;
 using Docker.DotNet.Models;
 using DotNet.Testcontainers.Builders;
 using DotNet.Testcontainers.Configurations;
 using JetBrains.Annotations;
 using Stef.Validation;
+using WireMock.Net.Testcontainers.Utils;
 
 namespace WireMock.Net.Testcontainers;
 
@@ -77,8 +77,8 @@ public sealed class WireMockConfiguration : ContainerConfiguration
         StaticMappingsPath = BuildConfiguration.Combine(oldValue.StaticMappingsPath, newValue.StaticMappingsPath);
         WatchStaticMappings = BuildConfiguration.Combine(oldValue.WatchStaticMappings, newValue.WatchStaticMappings);
         WatchStaticMappingsInSubdirectories = BuildConfiguration.Combine(oldValue.WatchStaticMappingsInSubdirectories, newValue.WatchStaticMappingsInSubdirectories);
-        AdditionalUrls = Combine(oldValue.AdditionalUrls, newValue.AdditionalUrls);
-        ProtoDefinitions = Combine(oldValue.ProtoDefinitions, newValue.ProtoDefinitions);
+        AdditionalUrls = CombineUtils.Combine(oldValue.AdditionalUrls, newValue.AdditionalUrls);
+        ProtoDefinitions = CombineUtils.Combine(oldValue.ProtoDefinitions, newValue.ProtoDefinitions);
     }
 
     /// <summary>
@@ -130,16 +130,4 @@ public sealed class WireMockConfiguration : ContainerConfiguration
 
         return this;
     }
-
-    private static List<T> Combine<T>(List<T> oldValue, List<T> newValue)
-    {
-        return oldValue.Concat(newValue).ToList();
-    }
-
-    private static Dictionary<TKey, TValue> Combine<TKey, TValue>(Dictionary<TKey, TValue> oldValue, Dictionary<TKey, TValue> newValue)
-    {
-        return newValue
-            .Concat(oldValue.Where(item => !newValue.Keys.Contains(item.Key)))
-            .ToDictionary(item => item.Key, item => item.Value);
-    }
 }
\ No newline at end of file
diff --git a/src/WireMock.Net.Testcontainers/WireMockContainer.cs b/src/WireMock.Net.Testcontainers/WireMockContainer.cs
index 002a0469..f34cc1b3 100644
--- a/src/WireMock.Net.Testcontainers/WireMockContainer.cs
+++ b/src/WireMock.Net.Testcontainers/WireMockContainer.cs
@@ -228,6 +228,7 @@ public sealed class WireMockContainer : DockerContainer
         foreach (var kvp in _configuration.ProtoDefinitions)
         {
             Logger.LogInformation("Adding ProtoDefinition {Id}", kvp.Key);
+
             foreach (var protoDefinition in kvp.Value)
             {
                 try
diff --git a/src/WireMock.Net.Testcontainers/WireMockContainerBuilder.cs b/src/WireMock.Net.Testcontainers/WireMockContainerBuilder.cs
index 71c0ad69..37241598 100644
--- a/src/WireMock.Net.Testcontainers/WireMockContainerBuilder.cs
+++ b/src/WireMock.Net.Testcontainers/WireMockContainerBuilder.cs
@@ -2,6 +2,8 @@
 
 using System;
 using System.Linq;
+using System.Net;
+using System.Net.Http;
 using System.Runtime.InteropServices;
 using Docker.DotNet.Models;
 using DotNet.Testcontainers.Builders;
@@ -250,6 +252,23 @@ public sealed class WireMockContainerBuilder : ContainerBuilder<WireMockContaine
 
         builder.Validate();
 
+        var waitForContainerOS = _imageOS == OSPlatform.Windows ? Wait.ForWindowsContainer() : Wait.ForUnixContainer();
+        builder
+            .WithWaitStrategy(waitForContainerOS
+                .UntilHttpRequestIsSucceeded(httpWaitStrategy => httpWaitStrategy
+                    .ForPort(WireMockContainer.ContainerPort)
+                    .WithMethod(HttpMethod.Get)
+                    .WithBasicAuthentication(DockerResourceConfiguration)
+                    .ForPath("/__admin/health")
+                    .ForStatusCode(HttpStatusCode.OK)
+                    .ForResponseMessageMatching(async httpResponseMessage =>
+                    {
+                        var content = await httpResponseMessage.Content.ReadAsStringAsync();
+                        return content?.Contains("Healthy") == true;
+                    })
+                )
+        );
+
         return new WireMockContainer(builder.DockerResourceConfiguration);
     }
 
@@ -262,7 +281,9 @@ public sealed class WireMockContainerBuilder : ContainerBuilder<WireMockContaine
         return builder
             .WithPortBinding(WireMockContainer.ContainerPort, true)
             .WithCommand($"--WireMockLogger {DefaultLogger}")
-            .WithWaitStrategy(waitForContainerOS.UntilMessageIsLogged("WireMock.Net server running"));
+            .WithWaitStrategy(waitForContainerOS
+                .UntilMessageIsLogged("WireMock.Net server running", waitStrategy => waitStrategy.WithTimeout(TimeSpan.FromSeconds(30)))
+            );
     }
 
     /// <inheritdoc />
diff --git a/test/WireMock.Net.Tests/Testcontainers/CombineUtilsTests.cs b/test/WireMock.Net.Tests/Testcontainers/CombineUtilsTests.cs
new file mode 100644
index 00000000..95f55774
--- /dev/null
+++ b/test/WireMock.Net.Tests/Testcontainers/CombineUtilsTests.cs
@@ -0,0 +1,161 @@
+// Copyright © WireMock.Net
+
+using System.Collections.Generic;
+using FluentAssertions;
+using WireMock.Net.Testcontainers.Utils;
+using Xunit;
+
+namespace WireMock.Net.Tests.Testcontainers;
+
+public class CombineUtilsTests
+{
+    [Fact]
+    public void Combine_Lists_WithBothEmpty_ReturnsEmptyList()
+    {
+        // Arrange
+        var oldValue = new List<string>();
+        var newValue = new List<string>();
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void Combine_Lists_WithEmptyOldValue_ReturnsNewValue()
+    {
+        // Arrange
+        var oldValue = new List<string>();
+        var newValue = new List<string> { "item1", "item2" };
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().Equal("item1", "item2");
+    }
+
+    [Fact]
+    public void Combine_Lists_WithEmptyNewValue_ReturnsOldValue()
+    {
+        // Arrange
+        var oldValue = new List<string> { "item1", "item2" };
+        var newValue = new List<string>();
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().Equal("item1", "item2");
+    }
+
+    [Fact]
+    public void Combine_Lists_WithBothPopulated_ReturnsConcatenatedList()
+    {
+        // Arrange
+        var oldValue = new List<int> { 1, 2, 3 };
+        var newValue = new List<int> { 4, 5, 6 };
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().Equal(1, 2, 3, 4, 5, 6);
+    }
+
+    [Fact]
+    public void Combine_Lists_WithDuplicates_RemovesDuplicates()
+    {
+        // Arrange
+        var oldValue = new List<string> { "a", "b", "c" };
+        var newValue = new List<string> { "b", "c", "d" };
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().Equal("a", "b", "c", "d");
+    }
+
+    [Fact]
+    public void Combine_Dictionaries_WithBothEmpty_ReturnsEmptyDictionary()
+    {
+        // Arrange
+        var oldValue = new Dictionary<string, int>();
+        var newValue = new Dictionary<string, int>();
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void Combine_Dictionaries_WithEmptyOldValue_ReturnsNewValue()
+    {
+        // Arrange
+        var oldValue = new Dictionary<string, int>();
+        var newValue = new Dictionary<string, int>
+        {
+            { "key1", 1 },
+            { "key2", 2 }
+        };
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().HaveCount(2);
+        result["key1"].Should().Be(1);
+        result["key2"].Should().Be(2);
+    }
+
+    [Fact]
+    public void Combine_Dictionaries_WithEmptyNewValue_ReturnsOldValue()
+    {
+        // Arrange
+        var oldValue = new Dictionary<string, int>
+        {
+            { "key1", 1 },
+            { "key2", 2 }
+        };
+        var newValue = new Dictionary<string, int>();
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().HaveCount(2);
+        result["key1"].Should().Be(1);
+        result["key2"].Should().Be(2);
+    }
+
+    [Fact]
+    public void Combine_Dictionaries_WithNoOverlappingKeys_ReturnsMergedDictionary()
+    {
+        // Arrange
+        var oldValue = new Dictionary<string, string>
+        {
+            { "key1", "value1" },
+            { "key2", "value2" }
+        };
+        var newValue = new Dictionary<string, string>
+        {
+            { "key3", "value3" },
+            { "key4", "value4" }
+        };
+
+        // Act
+        var result = CombineUtils.Combine(oldValue, newValue);
+
+        // Assert
+        result.Should().HaveCount(4);
+        result["key1"].Should().Be("value1");
+        result["key2"].Should().Be("value2");
+        result["key3"].Should().Be("value3");
+        result["key4"].Should().Be("value4");
+    }
+}
\ No newline at end of file
diff --git a/test/WireMock.Net.Tests/Testcontainers/TestcontainersTestsGrpc.cs b/test/WireMock.Net.Tests/Testcontainers/TestcontainersTestsGrpc.cs
index c05125e0..1c578f78 100644
--- a/test/WireMock.Net.Tests/Testcontainers/TestcontainersTestsGrpc.cs
+++ b/test/WireMock.Net.Tests/Testcontainers/TestcontainersTestsGrpc.cs
@@ -19,7 +19,7 @@ using Xunit.Abstractions;
 
 namespace WireMock.Net.Tests.Testcontainers;
 
-[Collection("Grpc")]
+//[Collection("Grpc")]
 public class TestcontainersTestsGrpc(ITestOutputHelper testOutputHelper)
 {
     [Fact]
@@ -37,7 +37,7 @@ public class TestcontainersTestsGrpc(ITestOutputHelper testOutputHelper)
             .WithCommand("--Urls", $"http://*:80 grpc://*:{port}")
             .WithPortBinding(port, true)
             .Build();
-        
+
         try
         {
             await wireMockContainer.StartAsync();
@@ -171,6 +171,35 @@ public class TestcontainersTestsGrpc(ITestOutputHelper testOutputHelper)
         await StopAsync(wireMockContainer);
     }
 
+    private async Task<HelloReply> When_GrpcClient_Calls_SayHelloAsync(WireMockContainer wireMockContainer)
+    {
+        var address = wireMockContainer.GetPublicUrls().First(x => x.Key != 80).Value;
+        var channel = GrpcChannel.ForAddress(address);
+
+        var client = new Greeter.GreeterClient(channel);
+
+        try
+        {
+            return await client.SayHelloAsync(new HelloRequest { Name = "stef" });
+        }
+        catch (Exception ex)
+        {
+            testOutputHelper.WriteLine("Exception during GrpcClient Call to {0}. Exception = {1}.", address, ex);
+
+            testOutputHelper.WriteLine("Dumping WireMock.Net logs:");
+            var (stdOut, stdError) = await wireMockContainer.GetLogsAsync(DateTime.MinValue);
+            testOutputHelper.WriteLine("Out  :\r\n{0}", stdOut);
+            testOutputHelper.WriteLine("Error:\r\n{0}", stdError);
+
+            testOutputHelper.WriteLine("Dumping WireMock.Net mappings:");
+            using var httpClient = wireMockContainer.CreateClient();
+            using var response = await httpClient.GetAsync("/__admin/mappings");
+            var mappings = await response.Content.ReadAsStringAsync();
+            testOutputHelper.WriteLine("Mappings:\r\n{0}", mappings);
+            throw;
+        }
+    }
+
     private async Task StopAsync(WireMockContainer wireMockContainer)
     {
         try
@@ -240,18 +269,6 @@ public class TestcontainersTestsGrpc(ITestOutputHelper testOutputHelper)
 
         var result = await httpClient.PostAsync("/__admin/mappings", new StringContent(mappingsJson, Encoding.UTF8, WireMockConstants.ContentTypeJson));
         result.EnsureSuccessStatusCode();
-
-        await Task.Delay(5000);
-    }
-
-    private static async Task<HelloReply> When_GrpcClient_Calls_SayHelloAsync(WireMockContainer wireMockContainer)
-    {
-        var address = wireMockContainer.GetPublicUrls().First(x => x.Key != 80).Value;
-        var channel = GrpcChannel.ForAddress(address);
-
-        var client = new Greeter.GreeterClient(channel);
-
-        return await client.SayHelloAsync(new HelloRequest { Name = "stef" });
     }
 
     private static void Then_ReplyMessage_Should_BeCorrect(HelloReply reply)
diff --git a/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj b/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
index de6ca818..b53868b9 100644
--- a/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
+++ b/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
@@ -30,6 +30,10 @@
         <Compile Remove="Util\JsonUtilsTests.cs" />
     </ItemGroup>
 
+    <ItemGroup>
+      <Compile Include="..\..\src\WireMock.Net.Testcontainers\Utils\CombineUtils.cs" Link="Testcontainers\CombineUtils.cs" />
+    </ItemGroup>
+
     <ItemGroup>
         <!-- https://stackoverflow.com/questions/59406201/filenesting-not-working-for-class-or-shared-library-projects -->
         <ProjectCapability Include="ConfigurableFileNesting" />