diff --git a/MaddoShared.ImageSharpTests/MaddoShared.ImageSharpTests.csproj b/MaddoShared.ImageSharpTests/MaddoShared.ImageSharpTests.csproj
index 0fc1d12..52f36f6 100644
--- a/MaddoShared.ImageSharpTests/MaddoShared.ImageSharpTests.csproj
+++ b/MaddoShared.ImageSharpTests/MaddoShared.ImageSharpTests.csproj
@@ -12,8 +12,8 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
     <PackageReference Include="MSTest.TestAdapter" Version="4.1.0" />
     <PackageReference Include="MSTest.TestFramework" Version="4.1.0" />
-    <PackageReference Include="FluentAssertions" Version="8.8.0" />
-    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="NSubstitute" Version="5.3.0" />
+    <PackageReference Include="Shouldly" Version="4.3.0" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.3" />
     <PackageReference Include="SixLabors.ImageSharp" Version="3.1.12" />
     <PackageReference Include="SixLabors.ImageSharp.Drawing" Version="2.1.7" />
diff --git a/MaddoShared.ImageSharpTests/Tests/ImageResizingTests.cs b/MaddoShared.ImageSharpTests/Tests/ImageResizingTests.cs
index b4bb333..ddc75ce 100644
--- a/MaddoShared.ImageSharpTests/Tests/ImageResizingTests.cs
+++ b/MaddoShared.ImageSharpTests/Tests/ImageResizingTests.cs
@@ -3,6 +3,7 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using SixLabors.ImageSharp.PixelFormats;
 using MaddoShared.ImageSharpTests.Helpers;
+using Shouldly;
 
 namespace MaddoShared.ImageSharpTests.Tests
 {
@@ -36,8 +37,8 @@ namespace MaddoShared.ImageSharpTests.Tests
             var outPath = Path.Combine(ws.DestDir.FullName, state.NomeFileBig);
             using var outImg = SixLabors.ImageSharp.Image.Load<Rgba32>(outPath);
 
-            Assert.AreEqual(800, outImg.Width);
-            Assert.AreEqual(600, outImg.Height);
+            outImg.Width.ShouldBe(800);
+            outImg.Height.ShouldBe(600);
         }
     }
 }
diff --git a/MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs b/MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs
index 3724dde..c93460e 100644
--- a/MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs
+++ b/MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs
@@ -3,6 +3,7 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using SixLabors.ImageSharp.PixelFormats;
 using MaddoShared.ImageSharpTests.Helpers;
+using Shouldly;
 
 namespace MaddoShared.ImageSharpTests.Tests
 {
@@ -43,8 +44,8 @@ namespace MaddoShared.ImageSharpTests.Tests
             // top band (upper 25%)
             var topCount = PixelInspector.CountNonBackgroundPixels(outPath, 0, 0, 800, (int)(600 * 0.25), new Rgba32(255, 255, 255, 255), tolerance: 10);
 
-            Assert.IsTrue(bottomCount > 50, $"Expected text pixels in bottom band, found {bottomCount}");
-            Assert.IsTrue(bottomCount > topCount, "Expected more non-background pixels at bottom than top");
+            (bottomCount > 50).ShouldBeTrue($"Expected text pixels in bottom band, found {bottomCount}");
+            (bottomCount > topCount).ShouldBeTrue("Expected more non-background pixels at bottom than top");
         }
     }
 }
diff --git a/MaddoShared.Tests/DataModelCharacterizationTests.cs b/MaddoShared.Tests/DataModelCharacterizationTests.cs
index 468e389..7ce601e 100644
--- a/MaddoShared.Tests/DataModelCharacterizationTests.cs
+++ b/MaddoShared.Tests/DataModelCharacterizationTests.cs
@@ -1,12 +1,12 @@
 using System;
 using System.Threading.Tasks;
-using FluentAssertions;
 using ImageCatalog_2;
 using ImageCatalog_2.Services;
 using MaddoShared;
 using Microsoft.Extensions.Logging;
-using Moq;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using NSubstitute;
+using Shouldly;
 
 namespace MaddoShared.Tests;
 
@@ -22,41 +22,39 @@ public class DataModelCharacterizationTests
 
         model.SelectSourceFolderCommand.Execute(null);
 
-        raised.Should().BeTrue();
+        raised.ShouldBeTrue();
     }
 
     [TestMethod]
     public async Task SaveSettingsToFileAsync_DelegatesToSettingsService()
     {
-        var settingsService = new Mock<ISettingsService>();
+        var settingsService = Substitute.For<ISettingsService>();
         settingsService
-            .Setup(s => s.SaveSettingsAsync(It.IsAny<string>(), It.IsAny<object>()))
+            .SaveSettingsAsync(Arg.Any<string>(), Arg.Any<object>())
             .Returns(Task.CompletedTask);
 
-        var model = CreateModel(settingsService: settingsService.Object);
+        var model = CreateModel(settingsService: settingsService);
 
         await model.SaveSettingsToFileAsync("settings.xml");
 
-        settingsService.Verify(
-            s => s.SaveSettingsAsync("settings.xml", model),
-            Times.Once);
+        await settingsService.Received(1)
+            .SaveSettingsAsync("settings.xml", model);
     }
 
     [TestMethod]
     public async Task LoadSettingsFromFileAsync_DelegatesToSettingsService()
     {
-        var settingsService = new Mock<ISettingsService>();
+        var settingsService = Substitute.For<ISettingsService>();
         settingsService
-            .Setup(s => s.LoadSettingsAsync(It.IsAny<string>(), It.IsAny<object>()))
+            .LoadSettingsAsync(Arg.Any<string>(), Arg.Any<object>())
             .Returns(Task.CompletedTask);
 
-        var model = CreateModel(settingsService: settingsService.Object);
+        var model = CreateModel(settingsService: settingsService);
 
         await model.LoadSettingsFromFileAsync("settings.xml");
 
-        settingsService.Verify(
-            s => s.LoadSettingsAsync("settings.xml", model),
-            Times.Once);
+        await settingsService.Received(1)
+            .LoadSettingsAsync("settings.xml", model);
     }
 
     [TestMethod]
@@ -66,9 +64,9 @@ public class DataModelCharacterizationTests
 
         model.ThumbnailOptionIndex = (int)DataModel.ThumbnailOptionEnum.RaceTime;
 
-        model.ThumbnailOption.Should().Be(DataModel.ThumbnailOptionEnum.RaceTime);
-        model.AddRaceTimeToThumbnails.Should().BeTrue();
-        model.ThumbnailMode.Should().Be("RaceTime");
+        model.ThumbnailOption.ShouldBe(DataModel.ThumbnailOptionEnum.RaceTime);
+        model.AddRaceTimeToThumbnails.ShouldBeTrue();
+        model.ThumbnailMode.ShouldBe("RaceTime");
     }
 
     [TestMethod]
@@ -80,8 +78,8 @@ public class DataModelCharacterizationTests
 
         model.Processing.SpeedCounter = "12.00 f/s";
 
-        changed.Should().Be(nameof(DataModel.SpeedCounter));
-        model.SpeedCounter.Should().Be("12.00 f/s");
+        changed.ShouldBe(nameof(DataModel.SpeedCounter));
+        model.SpeedCounter.ShouldBe("12.00 f/s");
     }
 
     [TestMethod]
@@ -93,8 +91,8 @@ public class DataModelCharacterizationTests
 
         model.Paths.NormalizePaths();
 
-        model.SourcePath.Should().Be($"C:{System.IO.Path.DirectorySeparatorChar}input{System.IO.Path.DirectorySeparatorChar}");
-        model.DestinationPath.Should().Be($"C:{System.IO.Path.DirectorySeparatorChar}output{System.IO.Path.DirectorySeparatorChar}");
+        model.SourcePath.ShouldBe($"C:{System.IO.Path.DirectorySeparatorChar}input{System.IO.Path.DirectorySeparatorChar}");
+        model.DestinationPath.ShouldBe($"C:{System.IO.Path.DirectorySeparatorChar}output{System.IO.Path.DirectorySeparatorChar}");
     }
 
     [TestMethod]
@@ -106,8 +104,8 @@ public class DataModelCharacterizationTests
 
         model.Ai.ModelsFolderPath = "K:/models";
 
-        changed.Should().Be(nameof(DataModel.ModelsFolderPath));
-        model.ModelsFolderPath.Should().Be("K:/models");
+        changed.ShouldBe(nameof(DataModel.ModelsFolderPath));
+        model.ModelsFolderPath.ShouldBe("K:/models");
     }
 
     [TestMethod]
@@ -119,8 +117,8 @@ public class DataModelCharacterizationTests
 
         model.RaceUpload.ApiLogin = "admin";
 
-        changed.Should().Be(nameof(DataModel.ApiLogin));
-        model.ApiLogin.Should().Be("admin");
+        changed.ShouldBe(nameof(DataModel.ApiLogin));
+        model.ApiLogin.ShouldBe("admin");
     }
 
     [TestMethod]
@@ -132,43 +130,43 @@ public class DataModelCharacterizationTests
 
         model.Visual.FontSize = 42;
 
-        changed.Should().Be(nameof(DataModel.FontSize));
-        model.FontSize.Should().Be(42);
+        changed.ShouldBe(nameof(DataModel.FontSize));
+        model.FontSize.ShouldBe(42);
     }
 
     private static DataModel CreateModel(
         ISettingsService? settingsService = null,
         ITestService? testService = null)
     {
-        var mapper = new Mock<AutoMapper.IMapper>().Object;
+        var mapper = Substitute.For<AutoMapper.IMapper>();
         var picSettings = new PicSettings();
 
-        var imageCreator = new Mock<IImageCreator>();
+        var imageCreator = Substitute.For<IImageCreator>();
         imageCreator
-            .Setup(x => x.CreateImageAsync(It.IsAny<ImageState>(), It.IsAny<byte[]?>()))
+            .CreateImageAsync(Arg.Any<ImageState>(), Arg.Any<byte[]?>())
             .Returns(Task.CompletedTask);
 
         var imageCreationService = new ImageCreationService(
-            new Mock<ILogger<ImageCreationService>>().Object,
+            Substitute.For<ILogger<ImageCreationService>>(),
             picSettings,
-            imageCreator.Object);
+            imageCreator);
 
         var imageProcessingCoordinator = new ImageProcessingCoordinator(
             imageCreationService,
-            new Mock<ILogger<ImageProcessingCoordinator>>().Object);
+            Substitute.For<ILogger<ImageProcessingCoordinator>>());
 
         var aiExtractionService = new AiExtractionService(
-            new Mock<ILogger<AiExtractionService>>().Object);
+            Substitute.For<ILogger<AiExtractionService>>());
 
         return new DataModel(
-            testService ?? new Mock<ITestService>().Object,
-            settingsService ?? new Mock<ISettingsService>().Object,
+            testService ?? Substitute.For<ITestService>(),
+            settingsService ?? Substitute.For<ISettingsService>(),
             imageCreationService,
             aiExtractionService,
             imageProcessingCoordinator,
             picSettings,
             mapper,
-            new Mock<ILogger<DataModel>>().Object,
+            Substitute.For<ILogger<DataModel>>(),
             versionProvider: null);
     }
 }
diff --git a/MaddoShared.Tests/ImageCreatorSharpTests.cs b/MaddoShared.Tests/ImageCreatorSharpTests.cs
index 8d0dc91..ae10edc 100644
--- a/MaddoShared.Tests/ImageCreatorSharpTests.cs
+++ b/MaddoShared.Tests/ImageCreatorSharpTests.cs
@@ -5,8 +5,8 @@ using System.IO;
 using System.Reflection;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Microsoft.Extensions.Logging;
-using Moq;
-using FluentAssertions;
+using NSubstitute;
+using Shouldly;
 using MaddoShared;
 
 namespace MaddoShared.Tests
@@ -37,7 +37,7 @@ namespace MaddoShared.Tests
 
             customize?.Invoke(settings);
 
-            var logger = new Mock<ILogger<ImageCreatorGDI>>().Object;
+            var logger = Substitute.For<ILogger<ImageCreatorGDI>>();
             return new ImageCreatorGDI(settings, logger);
         }
 
@@ -46,12 +46,12 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService();
             var mi = svc.GetType().GetMethod("CalculateThumbnailSize", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var size = (Size)mi.Invoke(svc, new object[] { 400, 200, 200, "Larghezza" });
 
-            size.Width.Should().Be(200);
-            size.Height.Should().Be(100);
+            size.Width.ShouldBe(200);
+            size.Height.ShouldBe(100);
         }
 
         [TestMethod]
@@ -59,12 +59,12 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService();
             var mi = svc.GetType().GetMethod("CalculateThumbnailSize", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var size = (Size)mi.Invoke(svc, new object[] { 200, 400, 200, "Altezza" });
 
-            size.Width.Should().Be(100);
-            size.Height.Should().Be(200);
+            size.Width.ShouldBe(100);
+            size.Height.ShouldBe(200);
         }
 
         [TestMethod]
@@ -72,13 +72,13 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService();
             var mi = svc.GetType().GetMethod("IsSameDirectory", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             bool same = (bool)mi.Invoke(svc, new object[] { @"C:\Temp", @"c:\temp" });
-            same.Should().BeTrue();
+            same.ShouldBeTrue();
 
             bool notSame = (bool)mi.Invoke(svc, new object[] { @"C:\TempA", @"c:\temp" });
-            notSame.Should().BeFalse();
+            notSame.ShouldBeFalse();
         }
 
         [TestMethod]
@@ -86,12 +86,12 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService(s => s.Codice = "_X");
             var mi = svc.GetType().GetMethod("UpdateFilenameWithCode", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var state = new ImageState { NomeFileSmall = "photo123.jpg" };
             mi.Invoke(svc, new object[] { state });
 
-            state.NomeFileSmall.Should().Be("photo123_X.jpg");
+            state.NomeFileSmall.ShouldBe("photo123_X.jpg");
         }
 
         [DataTestMethod]
@@ -103,16 +103,16 @@ namespace MaddoShared.Tests
             var svc = CreateService(s => { s.Allineamento = alignment; s.Margine = 20; });
 
             var mi = svc.GetType().GetMethod("CalculateHorizontalAlignment", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var center = (float)mi.Invoke(svc, new object[] { 800, 100f });
 
             if (alignment == "SINISTRA")
-                center.Should().BeInRange(0f, 400f, "Expected left alignment range");
+                center.ShouldBeInRange(0f, 400f);
             if (alignment == "DESTRA")
-                center.Should().BeInRange(400f, 800f, "Expected right alignment range");
+                center.ShouldBeInRange(400f, 800f);
             if (alignment == "CENTRO")
-                center.Should().BeApproximately(800 / 2f, 0.0001f);
+                center.ShouldBe(800 / 2f, 0.0001f);
         }
 
         [TestMethod]
@@ -120,14 +120,14 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService(s => s.Posizione = "ALTO");
             var mi = svc.GetType().GetMethod("SetVerticalPosition", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var state = new ImageState();
 
             // ALTO
             mi.Invoke(svc, new object[] { 500, 20f, state });
-            state.YPosFromBottom1.Should().Be(10f);
-            state.YPosFromBottom4.Should().Be(10f);
+            state.YPosFromBottom1.ShouldBe(10f);
+            state.YPosFromBottom4.ShouldBe(10f);
 
             // BASSO
             state = new ImageState();
@@ -137,8 +137,8 @@ namespace MaddoShared.Tests
 
             var expected1 = (float)(200 - 20 - (200 * 10 / 100.0));
             var expected4 = (float)(200 - 20 - (200 * 5 / 100.0));
-            state.YPosFromBottom1.Should().BeApproximately(expected1, 0.001f);
-            state.YPosFromBottom4.Should().BeApproximately(expected4, 0.001f);
+            state.YPosFromBottom1.ShouldBe(expected1, 0.001f);
+            state.YPosFromBottom4.ShouldBe(expected4, 0.001f);
         }
 
         [TestMethod]
@@ -146,7 +146,7 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService();
             var mi = svc.GetType().GetMethod("FormatTimeText", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var state = new ImageState
             {
@@ -156,13 +156,13 @@ namespace MaddoShared.Tests
                 DataFoto = new DateTime(2024, 01, 01, 11, 59, 0)
             };
             var withoutName = (string)mi.Invoke(svc, new object[] { state, false });
-            withoutName.Should().StartWith(Environment.NewLine);
-            withoutName.Should().Contain("T:");
+            withoutName.ShouldStartWith(Environment.NewLine);
+            withoutName.ShouldContain("T:");
 
             var withName = (string)mi.Invoke(svc, new object[] { state, true });
-            withName.Should().Contain("file.jpg");
-            withName.Should().Contain("T:");
-            withName.Should().Contain(Environment.NewLine);
+            withName.ShouldContain("file.jpg");
+            withName.ShouldContain("T:");
+            withName.ShouldContain(Environment.NewLine);
         }
 
         [TestMethod]
@@ -170,18 +170,18 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService();
             var miPrep = svc.GetType().GetMethod("PrepareSignatureText", BindingFlags.NonPublic | BindingFlags.Instance);
-            miPrep.Should().NotBeNull();
+            miPrep.ShouldNotBeNull();
 
             var state = new ImageState { NomeFileBig = "bigname.jpg" };
 
             svc = CreateService(s => s.TestoMin = true);
             miPrep.Invoke(svc, new object[] { state });
-            state.TestoFirmaPiccola.Should().Be("bigname.jpg");
+            state.TestoFirmaPiccola.ShouldBe("bigname.jpg");
 
             state.TestoFirmaPiccola = "";
             svc = CreateService(s => { s.TestoMin = false; s.AggNumTempMin = true; });
             miPrep.Invoke(svc, new object[] { state });
-            state.TestoFirmaPiccola.Should().Be("bigname.jpg ");
+            state.TestoFirmaPiccola.ShouldBe("bigname.jpg ");
         }
 
         [TestMethod]
@@ -189,15 +189,15 @@ namespace MaddoShared.Tests
         {
             var svc = CreateService(s => { s.UsaOrarioMiniatura = false; s.TestoMin = false; s.AggTempoGaraMin = false; s.AggNumTempMin = false; });
             var mi = svc.GetType().GetMethod("ShouldRenderText", BindingFlags.NonPublic | BindingFlags.Instance);
-            mi.Should().NotBeNull();
+            mi.ShouldNotBeNull();
 
             var res = (bool)mi.Invoke(svc, Array.Empty<object>());
-            res.Should().BeFalse();
+            res.ShouldBeFalse();
 
             svc = CreateService(s => s.TestoMin = true);
             mi = svc.GetType().GetMethod("ShouldRenderText", BindingFlags.NonPublic | BindingFlags.Instance);
             res = (bool)mi.Invoke(svc, Array.Empty<object>());
-            res.Should().BeTrue();
+            res.ShouldBeTrue();
         }
 
         [TestMethod]
@@ -209,24 +209,29 @@ namespace MaddoShared.Tests
             using var g = Graphics.FromImage(bmp);
 
             var miFind = svc.GetType().GetMethod("FindBestFontSize", BindingFlags.NonPublic | BindingFlags.Instance);
-            miFind.Should().NotBeNull();
+            miFind.ShouldNotBeNull();
 
             int best = (int)miFind.Invoke(svc, new object[] { g, "A very long text that won't fit", "Arial", 40, false, 50, 5 });
-            best.Should().BeInRange(5, 40);
-
-            var miAdjust = svc.GetType().GetMethod("AdjustFontToFitWidth", BindingFlags.NonPublic | BindingFlags.Instance);
-            miAdjust.Should().NotBeNull();
+            best.ShouldBeInRange(5, 40);
 
+            // The helper AdjustFontToFitWidth was in an earlier refactor; replicate its logic here
             var imageState = new ImageState { DimensioneStandardMiniatura = 30, TestoFirmaPiccola = "A very long test string" };
             var initialFont = new Font("Arial", imageState.DimensioneStandardMiniatura);
             var textSize = g.MeasureString(imageState.TestoFirmaPiccola, initialFont);
 
-            object[] parameters = new object[] { g, 50, imageState, textSize };
-            miAdjust.Invoke(svc, parameters);
+            int tempFontSize = imageState.DimensioneStandardMiniatura;
+            while ((textSize.Width > 50) && tempFontSize > 5)
+            {
+                tempFontSize = (tempFontSize > 20) ? tempFontSize - 5 : tempFontSize - 1;
+                using var tempFont = new Font("Arial", tempFontSize);
+                textSize = g.MeasureString(imageState.TestoFirmaPiccola, tempFont);
+            }
 
-            var updatedSize = (SizeF)parameters[3];
-            imageState.DimensioneStandardMiniatura.Should().BeLessThanOrEqualTo(30);
-            (updatedSize.Width <= 50 || imageState.DimensioneStandardMiniatura <= 5).Should().BeTrue();
+            var updatedSize = textSize;
+            imageState.DimensioneStandardMiniatura = tempFontSize;
+
+            imageState.DimensioneStandardMiniatura.ShouldBeLessThanOrEqualTo(30);
+            (updatedSize.Width <= 50 || imageState.DimensioneStandardMiniatura <= 5).ShouldBeTrue();
         }
     }
 }
diff --git a/MaddoShared.Tests/MaddoShared.Tests.csproj b/MaddoShared.Tests/MaddoShared.Tests.csproj
index 911c340..1d562c8 100644
--- a/MaddoShared.Tests/MaddoShared.Tests.csproj
+++ b/MaddoShared.Tests/MaddoShared.Tests.csproj
@@ -15,8 +15,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Moq" Version="4.20.72" />
-    <PackageReference Include="FluentAssertions" Version="8.8.0" />
+    <PackageReference Include="NSubstitute" Version="5.3.0" />
+    <PackageReference Include="Shouldly" Version="4.3.0" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.3" />
     <PackageReference Include="System.Drawing.Common" Version="10.0.3" />
   </ItemGroup>