Improve code coverage

.github/copilot-instructions.md

@@ -111,28 +111,34 @@ images/                 # Project images and assets
 
 ### Unit Testing Patterns
 
-All new code must include unit tests following the pattern used in `Refitter.Tests.Scenarios` namespace:
+All new code must include unit tests following the pattern used in `Refitter.Tests.Scenarios` namespace.
+
+The project uses **TUnit v1.47.0** as its testing framework (not xUnit). TUnit provides significantly faster test execution (3x faster than xUnit), which improves both local development and CI/CD pipeline performance.
+
+Use TUnit's `[Test]` attribute for test methods:
 
 ```csharp
+using TUnit.Core;
+
 public class MyFeatureTests
 {
     private const string OpenApiSpec = @"..."; // OpenAPI specification
 
-    [Fact]
+    [Test]
     public async Task Can_Generate_Code()
     {
         string generatedCode = await GenerateCode();
         generatedCode.Should().NotBeNullOrWhiteSpace();
     }
 
-    [Fact]
+    [Test]
     public async Task Generated_Code_Contains_Expected_Pattern()
     {
         string generatedCode = await GenerateCode();
         generatedCode.Should().Contain("ExpectedPattern");
     }
 
-    [Fact]
+    [Test]
     public async Task Can_Build_Generated_Code()
     {
         string generatedCode = await GenerateCode();

src/Refitter.Tests/FormParameterExtractorTests.cs

@@ -0,0 +1,253 @@
+using System.Runtime.CompilerServices;
+using FluentAssertions;
+using NJsonSchema;
+using NSwag;
+using NSwag.CodeGeneration.CSharp.Models;
+using Refitter.Core;
+using TUnit.Core;
+
+namespace Refitter.Tests;
+
+public class FormParameterExtractorTests
+{
+    [Test]
+    public void CanExtract_Returns_True_For_FormData()
+    {
+        var extractor = new FormParameterExtractor();
+        extractor.CanExtract(OpenApiParameterKind.FormData).Should().BeTrue();
+    }
+
+    [Test]
+    public void CanExtract_Returns_False_For_Non_FormData()
+    {
+        var extractor = new FormParameterExtractor();
+        extractor.CanExtract(OpenApiParameterKind.Query).Should().BeFalse();
+        extractor.CanExtract(OpenApiParameterKind.Path).Should().BeFalse();
+        extractor.CanExtract(OpenApiParameterKind.Header).Should().BeFalse();
+        extractor.CanExtract(OpenApiParameterKind.Body).Should().BeFalse();
+    }
+
+    [Test]
+    public void Extract_Returns_Empty_When_No_FormData_Parameters()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation();
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings());
+        result.Should().BeEmpty();
+    }
+
+    [Test]
+    public void Extract_Returns_FormData_Parameters_With_Correct_Format()
+    {
+        var extractor = new FormParameterExtractor();
+        var parameter = CreateFormDataParameterModel("field1", "field1", "string");
+        var operationModel = CreateOperationModel(parameter);
+        var operation = new OpenApiOperation();
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().ContainSingle().Which.Should().Be("string field1");
+    }
+
+    [Test]
+    public void Extract_Handles_Alias_For_Different_Variable_Name()
+    {
+        var extractor = new FormParameterExtractor();
+        var parameter = CreateFormDataParameterModel("field-name", "field_name", "string");
+        var operationModel = CreateOperationModel(parameter);
+        var operation = new OpenApiOperation();
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().ContainSingle().Which.Should().Be("[AliasAs(\"field-name\")] string field_name");
+    }
+
+    [Test]
+    public void Extract_Deduplicates_FormData_Parameters_By_Variable_Name()
+    {
+        var extractor = new FormParameterExtractor();
+        var parameter1 = CreateFormDataParameterModel("field1", "field1", "string");
+        var parameter2 = CreateFormDataParameterModel("field1", "field1", "int");
+        var operationModel = CreateOperationModel(parameter1, parameter2);
+        var operation = new OpenApiOperation();
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().ContainSingle();
+    }
+
+    [Test]
+    public void Extract_Extracts_Multipart_Text_Fields_From_RequestBody()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation
+        {
+            RequestBody = new OpenApiRequestBody()
+        };
+        var schema = new JsonSchema();
+        schema.Properties["title"] = new JsonSchemaProperty
+        {
+            Type = JsonObjectType.String
+        };
+        schema.Properties["description"] = new JsonSchemaProperty
+        {
+            Type = JsonObjectType.String
+        };
+        operation.RequestBody.Content["multipart/form-data"] = new OpenApiMediaType
+        {
+            Schema = schema
+        };
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+
+        result.Should().HaveCount(2);
+        result.Should().Contain("string title");
+        result.Should().Contain("string description");
+    }
+
+    [Test]
+    public void Extract_Skips_Binary_Fields_From_Multipart_RequestBody()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation
+        {
+            RequestBody = new OpenApiRequestBody()
+        };
+        var schema = new JsonSchema();
+        schema.Properties["avatar"] = new JsonSchemaProperty
+        {
+            Type = JsonObjectType.String,
+            Format = "binary"
+        };
+        schema.Properties["title"] = new JsonSchemaProperty
+        {
+            Type = JsonObjectType.String
+        };
+        operation.RequestBody.Content["multipart/form-data"] = new OpenApiMediaType
+        {
+            Schema = schema
+        };
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+
+        result.Should().ContainSingle().Which.Should().Be("string title");
+    }
+
+    [Test]
+    public void Extract_Skips_Array_Of_Binary_From_Multipart_RequestBody()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation
+        {
+            RequestBody = new OpenApiRequestBody()
+        };
+        var schema = new JsonSchema();
+        schema.Properties["files"] = new JsonSchemaProperty
+        {
+            Type = JsonObjectType.Array,
+            Item = new JsonSchema
+            {
+                Type = JsonObjectType.String,
+                Format = "binary"
+            }
+        };
+        operation.RequestBody.Content["multipart/form-data"] = new OpenApiMediaType
+        {
+            Schema = schema
+        };
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().BeEmpty();
+    }
+
+    [Test]
+    public void Extract_Handles_Missing_RequestBody_Schema()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation
+        {
+            RequestBody = new OpenApiRequestBody()
+        };
+        operation.RequestBody.Content["multipart/form-data"] = new OpenApiMediaType();
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().BeEmpty();
+    }
+
+    [Test]
+    public void Extract_Handles_Null_RequestBody_Properties()
+    {
+        var extractor = new FormParameterExtractor();
+        var operationModel = CreateEmptyOperationModel();
+        var operation = new OpenApiOperation
+        {
+            RequestBody = new OpenApiRequestBody()
+        };
+        var schema = new JsonSchema();
+        operation.RequestBody.Content["multipart/form-data"] = new OpenApiMediaType
+        {
+            Schema = schema
+        };
+
+        var result = extractor.Extract(operationModel, operation, new RefitGeneratorSettings()).ToList();
+        result.Should().BeEmpty();
+    }
+
+    private static CSharpOperationModel CreateEmptyOperationModel()
+    {
+        var operationModel = (CSharpOperationModel)RuntimeHelpers.GetUninitializedObject(typeof(CSharpOperationModel));
+        var baseType = typeof(CSharpOperationModel).BaseType!;
+
+        baseType
+            .GetField("<Parameters>k__BackingField", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(operationModel, new List<CSharpParameterModel>());
+
+        return operationModel;
+    }
+
+    private static CSharpOperationModel CreateOperationModel(params CSharpParameterModel[] parameters)
+    {
+        var operationModel = (CSharpOperationModel)RuntimeHelpers.GetUninitializedObject(typeof(CSharpOperationModel));
+        var baseType = typeof(CSharpOperationModel).BaseType!;
+
+        baseType
+            .GetField("<Parameters>k__BackingField", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(operationModel, parameters.ToList());
+
+        return operationModel;
+    }
+
+    private static CSharpParameterModel CreateFormDataParameterModel(
+        string name,
+        string variableName,
+        string type = "string")
+    {
+        var parameterModel = (CSharpParameterModel)RuntimeHelpers.GetUninitializedObject(typeof(CSharpParameterModel));
+        var baseType = typeof(CSharpParameterModel).BaseType!;
+
+        baseType
+            .GetField("<Type>k__BackingField", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(parameterModel, type);
+        baseType
+            .GetField("<Name>k__BackingField", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(parameterModel, name);
+        baseType
+            .GetField("<VariableName>k__BackingField", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(parameterModel, variableName);
+        baseType
+            .GetField("_parameter", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!
+            .SetValue(
+                parameterModel,
+                new OpenApiParameter
+                {
+                    Name = name,
+                    Kind = OpenApiParameterKind.FormData,
+                    Schema = new JsonSchema()
+                });
+
+        return parameterModel;
+    }
+}