diff --git a/src/Criteo.OpenApi.Comparator.Cli/Program.cs b/src/Criteo.OpenApi.Comparator.Cli/Program.cs
index be741fd..cdfef57 100644
--- a/src/Criteo.OpenApi.Comparator.Cli/Program.cs
+++ b/src/Criteo.OpenApi.Comparator.Cli/Program.cs
@@ -136,13 +136,7 @@ private static void DisplayOutput(IEnumerable<ComparisonMessage> differences, Ou
         {
             if (outputFormat == OutputFormat.Json)
             {
-                var serializerOptions = new JsonSerializerOptions
-                {
-                    WriteIndented = true,
-                    Converters = { new JsonStringEnumConverter() },
-                    Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
-                };
-                Console.WriteLine(JsonSerializer.Serialize(differences, serializerOptions));
+                Console.WriteLine(JsonSerializer.Serialize(differences, SerializationOptions));
                 return;
             }
 
@@ -154,5 +148,12 @@ private static void DisplayOutput(IEnumerable<ComparisonMessage> differences, Ou
                 }
             }
         }
+
+        private static readonly JsonSerializerOptions SerializationOptions = new()
+        {
+            WriteIndented = true,
+            Converters = { new JsonStringEnumConverter() },
+            Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
+        };
     }
 }
diff --git a/src/Criteo.OpenApi.Comparator.UTest/Criteo.OpenApi.Comparator.UTest.csproj b/src/Criteo.OpenApi.Comparator.UTest/Criteo.OpenApi.Comparator.UTest.csproj
index 6f93523..47dd5a1 100644
--- a/src/Criteo.OpenApi.Comparator.UTest/Criteo.OpenApi.Comparator.UTest.csproj
+++ b/src/Criteo.OpenApi.Comparator.UTest/Criteo.OpenApi.Comparator.UTest.csproj
@@ -11,7 +11,7 @@
     </Content>
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="NUnit" Version="3.13.3" />
+    <PackageReference Include="NUnit" Version="4.3.2" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
   </ItemGroup>
diff --git a/src/Criteo.OpenApi.Comparator.UTest/OpenApiParserTests.cs b/src/Criteo.OpenApi.Comparator.UTest/OpenApiParserTests.cs
index 72b74ea..ddf693d 100644
--- a/src/Criteo.OpenApi.Comparator.UTest/OpenApiParserTests.cs
+++ b/src/Criteo.OpenApi.Comparator.UTest/OpenApiParserTests.cs
@@ -41,7 +41,7 @@ public void OpenApiParser_Should_Return_Valid_OpenApi_Document_Object(string fil
         {
             var documentAsString = ReadOpenApiFile(fileName);
             var validOpenApiDocument = OpenApiParser.Parse(documentAsString, out _);
-            Assert.IsInstanceOf<JsonDocument<OpenApiDocument>>(validOpenApiDocument);
+            Assert.That(validOpenApiDocument, Is.InstanceOf<JsonDocument<OpenApiDocument>>());
         }
     }
 }
diff --git a/src/Criteo.OpenApi.Comparator.UTest/PrimitiveTypesExtensionTests.cs b/src/Criteo.OpenApi.Comparator.UTest/PrimitiveTypesExtensionTests.cs
index c17c269..3a1c340 100644
--- a/src/Criteo.OpenApi.Comparator.UTest/PrimitiveTypesExtensionTests.cs
+++ b/src/Criteo.OpenApi.Comparator.UTest/PrimitiveTypesExtensionTests.cs
@@ -15,7 +15,7 @@ public void DifferFrom_ShouldReturn_false_When_SameString()
         {
             const string oldString = "string";
             const string newString = "string";
-            Assert.IsFalse(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.False);
         }
 
         [Test]
@@ -23,7 +23,7 @@ public void DifferFrom_ShouldReturn_false_When_NullString()
         {
             const string oldString = null;
             const string newString = null;
-            Assert.IsFalse(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.False);
         }
 
         [Test]
@@ -31,7 +31,7 @@ public void DifferFrom_ShouldReturn_true_When_NullOldString()
         {
             const string oldString = null;
             const string newString = "string";
-            Assert.IsTrue(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.True);
         }
 
         [Test]
@@ -39,7 +39,7 @@ public void DifferFrom_ShouldReturn_true_When_NullNewString()
         {
             const string oldString = "string";
             const string newString = null;
-            Assert.IsTrue(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.True);
         }
 
         [Test]
@@ -47,7 +47,7 @@ public void DifferFrom_ShouldReturn_false_When_SameInteger()
         {
             int? oldInteger = 8;
             int? newInteger = 8;
-            Assert.IsFalse(oldInteger.DifferFrom(newInteger));
+            Assert.That(oldInteger.DifferFrom(newInteger), Is.False);
         }
 
         [Test]
@@ -55,7 +55,7 @@ public void DifferFrom_ShouldReturn_false_When_NullInteger()
         {
             int? oldInteger = null;
             int? newInteger = null;
-            Assert.IsFalse(oldInteger.DifferFrom(newInteger));
+            Assert.That(oldInteger.DifferFrom(newInteger), Is.False);
         }
 
         [Test]
@@ -63,14 +63,14 @@ public void DifferFrom_ShouldReturn_true_When_NullOldInteger()
         {
             int? oldInteger = null;
             int? newInteger = 8;
-            Assert.IsTrue(oldInteger.DifferFrom(newInteger));
+            Assert.That(oldInteger.DifferFrom(newInteger), Is.True);
         }
 
         [Test]
         public void DifferFrom_ShouldReturn_true_When_NullNewInteger()
         {
             int? oldInteger = 8;
-            Assert.IsTrue(oldInteger.DifferFrom(null));
+            Assert.That(oldInteger.DifferFrom(null), Is.True);
         }
 
         [Test]
@@ -78,7 +78,7 @@ public void DifferFrom_ShouldReturn_false_When_SameOpenApiInteger()
         {
             var oldInteger = new OpenApiInteger(8);
             var newInteger = new OpenApiInteger(8);
-            Assert.IsFalse(oldInteger.DifferFrom(newInteger));
+            Assert.That(oldInteger.DifferFrom(newInteger), Is.False);
         }
 
         [Test]
@@ -86,7 +86,7 @@ public void DifferFrom_ShouldReturn_true_When_DifferentOpenApiInteger()
         {
             var oldInteger = new OpenApiInteger(8);
             var newInteger = new OpenApiInteger(1);
-            Assert.IsTrue(oldInteger.DifferFrom(newInteger));
+            Assert.That(oldInteger.DifferFrom(newInteger), Is.True);
         }
 
         [Test]
@@ -94,7 +94,7 @@ public void DifferFrom_ShouldReturn_false_When_SameOpenApiBoolean()
         {
             var oldBoolean = new OpenApiBoolean(false);
             var newBoolean = new OpenApiBoolean(false);
-            Assert.IsFalse(oldBoolean.DifferFrom(newBoolean));
+            Assert.That(oldBoolean.DifferFrom(newBoolean), Is.False);
         }
 
         [Test]
@@ -102,7 +102,7 @@ public void DifferFrom_ShouldReturn_true_When_DifferentOpenApiBoolean()
         {
             var oldBoolean = new OpenApiBoolean(false);
             var newBoolean = new OpenApiBoolean(true);
-            Assert.IsTrue(oldBoolean.DifferFrom(newBoolean));
+            Assert.That(oldBoolean.DifferFrom(newBoolean), Is.True);
         }
 
         [Test]
@@ -110,7 +110,7 @@ public void DifferFrom_ShouldReturn_false_When_SameOpenApiString()
         {
             var oldString = new OpenApiString("string");
             var newString = new OpenApiString("string");
-            Assert.IsFalse(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.False);
         }
 
         [Test]
@@ -118,7 +118,7 @@ public void DifferFrom_ShouldReturn_true_When_DifferentOpenApiString()
         {
             var oldString = new OpenApiString("oldString");
             var newString = new OpenApiString("newString");
-            Assert.IsTrue(oldString.DifferFrom(newString));
+            Assert.That(oldString.DifferFrom(newString), Is.True);
         }
     }
 }