Add comprehensive unit test suite for ProjectR with 99 tests covering core business logic

ProjectR.Tests/DiagnosticsTests.cs

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+using FluentAssertions;
+using Microsoft.CodeAnalysis;
+using Xunit;
+
+namespace ProjectR.Tests.Diagnostic;
+
+public class DiagnosticsTests
+{
+    [Fact]
+    public void UnexpectedError_HasCorrectProperties()
+    {
+        // Arrange & Act
+        var diagnostic = ProjectR.Diagnostics.UnexpectedError;
+
+        // Assert
+        diagnostic.Id.Should().Be("PR0001");
+        diagnostic.Title.ToString().Should().Be("An unexpected error occurred");
+        diagnostic.MessageFormat.ToString().Should().Be("An unexpected error occurred during mapper generation: '{0}' StackTrace: {1}");
+        diagnostic.Category.Should().Be("ProjectR.Generator");
+        diagnostic.DefaultSeverity.Should().Be(DiagnosticSeverity.Error);
+        diagnostic.IsEnabledByDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public void MapperGenerationFailed_HasCorrectProperties()
+    {
+        // Arrange & Act
+        var diagnostic = ProjectR.Diagnostics.MapperGenerationFailed;
+
+        // Assert
+        diagnostic.Id.Should().Be("PR0002");
+        diagnostic.Title.ToString().Should().Be("Mapper generation failed");
+        diagnostic.MessageFormat.ToString().Should().Be("Failed to generate an implementation for mapper '{0}'");
+        diagnostic.Category.Should().Be("ProjectR.Generator");
+        diagnostic.DefaultSeverity.Should().Be(DiagnosticSeverity.Error);
+        diagnostic.IsEnabledByDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public void NoValidCreationMethod_HasCorrectProperties()
+    {
+        // Arrange & Act
+        var diagnostic = ProjectR.Diagnostics.NoValidCreationMethod;
+
+        // Assert
+        diagnostic.Id.Should().Be("PR0003");
+        diagnostic.Title.ToString().Should().Be("No valid creation method found");
+        diagnostic.MessageFormat.ToString().Should().Be("ProjectR could not find a valid constructor or static factory method to create an instance of '{0}' based on the source type.");
+        diagnostic.Category.Should().Be("ProjectR.Policies");
+        diagnostic.DefaultSeverity.Should().Be(DiagnosticSeverity.Error);
+        diagnostic.IsEnabledByDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public void UnmappableConstructorParameter_HasCorrectProperties()
+    {
+        // Arrange & Act
+        var diagnostic = ProjectR.Diagnostics.UnmappableConstructorParameter;
+
+        // Assert
+        diagnostic.Id.Should().Be("PR0004");
+        diagnostic.Title.ToString().Should().Be("Unmappable constructor parameter");
+        diagnostic.MessageFormat.ToString().Should().Be("The parameter '{0}' of the constructor for '{1}' could not be mapped from any source property.");
+        diagnostic.Category.Should().Be("ProjectR.Policies");
+        diagnostic.DefaultSeverity.Should().Be(DiagnosticSeverity.Error);
+        diagnostic.IsEnabledByDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public void UnmappedDestinationProperty_HasCorrectProperties()
+    {
+        // Arrange & Act
+        var diagnostic = ProjectR.Diagnostics.UnmappedDestinationProperty;
+
+        // Assert
+        diagnostic.Id.Should().Be("PR0005");
+        diagnostic.Title.ToString().Should().Be("Unmapped destination property");
+        diagnostic.MessageFormat.ToString().Should().Be("The property '{0}' on destination type '{1}' was not mapped.");
+        diagnostic.Category.Should().Be("ProjectR.Policies");
+        diagnostic.DefaultSeverity.Should().Be(DiagnosticSeverity.Warning);
+        diagnostic.IsEnabledByDefault.Should().BeTrue();
+    }
+}

ProjectR.Tests/DtoAttributeTests.cs

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+using ProjectR.Attributes;
+using FluentAssertions;
+using Xunit;
+
+namespace ProjectR.Tests.Attributes;
+
+public class DtoAttributeTests
+{
+    private class TestEntity { }
+    private class TestDto { }
+    private class TestMapper { }
+
+    [Fact]
+    public void DtoAttribute_Constructor_SetsEntityTypeCorrectly()
+    {
+        // Arrange & Act
+        var attribute = new DtoAttribute<TestEntity>();
+
+        // Assert
+        attribute.EntityType.Should().Be(typeof(TestEntity));
+    }
+
+    [Fact]
+    public void DtoMapperAttribute_Constructor_SetsEntityTypeAndMapperTypeCorrectly()
+    {
+        // Arrange & Act
+        var attribute = new DtoMapperAttribute<TestEntity, TestMapper>();
+
+        // Assert
+        attribute.EntityType.Should().Be(typeof(TestEntity));
+        attribute.MapperType.Should().Be(typeof(TestMapper));
+    }
+
+    [Fact]
+    public void DtoAttribute_HasCorrectAttributeUsage()
+    {
+        // Arrange & Act
+        var attributeUsage = typeof(DtoAttribute<>).GetCustomAttributes(typeof(AttributeUsageAttribute), false)
+            .Cast<AttributeUsageAttribute>()
+            .First();
+
+        // Assert
+        attributeUsage.ValidOn.Should().Be(AttributeTargets.Class);
+        attributeUsage.AllowMultiple.Should().BeTrue();
+        attributeUsage.Inherited.Should().BeTrue();
+    }
+
+    [Fact]
+    public void DtoMapperAttribute_HasCorrectAttributeUsage()
+    {
+        // Arrange & Act
+        var attributeUsage = typeof(DtoMapperAttribute<,>).GetCustomAttributes(typeof(AttributeUsageAttribute), false)
+            .Cast<AttributeUsageAttribute>()
+            .First();
+
+        // Assert
+        attributeUsage.ValidOn.Should().Be(AttributeTargets.Class);
+        attributeUsage.AllowMultiple.Should().BeTrue();
+        attributeUsage.Inherited.Should().BeTrue();
+    }
+
+    [Fact]
+    public void DtoMapperAttribute_InheritsFromDtoAttribute()
+    {
+        // Arrange & Act & Assert
+        typeof(DtoMapperAttribute<TestEntity, TestMapper>).Should().BeDerivedFrom<DtoAttribute<TestEntity>>();
+    }
+}

ProjectR.Tests/GlobalUsings.cs

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+global using Xunit;

ProjectR.Tests/LegacyMappingClassesTests.cs

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+using FluentAssertions;
+using Microsoft.CodeAnalysis;
+using Moq;
+using Xunit;
+
+namespace ProjectR.Tests.Mapping;
+
+public class LegacyMappingClassesTests
+{
+    [Fact]
+    public void MappingInstruction_IsAbstractBaseClass()
+    {
+        // Assert
+        typeof(MappingInstruction).Should().BeAbstract();
+    }
+
+    [Fact]
+    public void NestedObjectMapperMapping_InheritsFromMappingInstruction()
+    {
+        // Assert
+        typeof(NestedObjectMapperMapping).Should().BeDerivedFrom<MappingInstruction>();
+    }
+
+    [Fact]
+    public void NestedObjectMapperMapping_Properties_CanBeSetAndRetrieved()
+    {
+        // Arrange
+        var mockSourceProperty = new Mock<IPropertySymbol>();
+        var mockDestinationProperty = new Mock<IPropertySymbol>();
+        var mockMapperType = new Mock<INamedTypeSymbol>();
+        var mapping = new NestedObjectMapperMapping();
+
+        // Act
+        mapping.SourceProperty = mockSourceProperty.Object;
+        mapping.DestinationProperty = mockDestinationProperty.Object;
+        mapping.MapperType = mockMapperType.Object;
+
+        // Assert
+        mapping.SourceProperty.Should().Be(mockSourceProperty.Object);
+        mapping.DestinationProperty.Should().Be(mockDestinationProperty.Object);
+        mapping.MapperType.Should().Be(mockMapperType.Object);
+    }
+
+    [Fact]
+    public void ParameterMapping_Properties_CanBeSetAndRetrieved()
+    {
+        // Arrange
+        var mapping = new ParameterMapping();
+        var sourcePropertyName = "SourceProperty";
+        var destinationParameterName = "destinationParam";
+
+        // Act
+        mapping.SourcePropertyName = sourcePropertyName;
+        mapping.DestinationParameterName = destinationParameterName;
+
+        // Assert
+        mapping.SourcePropertyName.Should().Be(sourcePropertyName);
+        mapping.DestinationParameterName.Should().Be(destinationParameterName);
+    }
+
+    [Fact]
+    public void PropertyMapping_InheritsFromMappingInstruction()
+    {
+        // Assert
+        typeof(PropertyMapping).Should().BeDerivedFrom<MappingInstruction>();
+    }
+
+    [Fact]
+    public void PropertyMapping_Properties_CanBeSetAndRetrieved()
+    {
+        // Arrange
+        var mapping = new PropertyMapping();
+        var sourcePropertyName = "SourceProperty";
+        var destinationPropertyName = "DestinationProperty";
+
+        // Act
+        mapping.SourcePropertyName = sourcePropertyName;
+        mapping.DestinationPropertyName = destinationPropertyName;
+
+        // Assert
+        mapping.SourcePropertyName.Should().Be(sourcePropertyName);
+        mapping.DestinationPropertyName.Should().Be(destinationPropertyName);
+    }
+
+    [Fact]
+    public void PropertyMappingInstruction_IsAbstractBaseClass()
+    {
+        // Assert
+        typeof(PropertyMappingInstruction).Should().BeAbstract();
+    }
+
+    [Fact]
+    public void PropertyMappingInstruction_InheritsFromMappingInstruction()
+    {
+        // Assert
+        typeof(PropertyMappingInstruction).Should().BeDerivedFrom<MappingInstruction>();
+    }
+
+    [Fact]
+    public void PropertyMappingInstruction_Constructor_SetsDestinationProperty()
+    {
+        // Arrange
+        var mockDestinationProperty = new Mock<IPropertySymbol>();
+
+        // Act
+        var instruction = new TestPropertyMappingInstruction(mockDestinationProperty.Object);
+
+        // Assert
+        instruction.DestinationProperty.Should().Be(mockDestinationProperty.Object);
+    }
+
+    [Fact]
+    public void PropertyMappingInstruction_DestinationProperty_IsReadOnly()
+    {
+        // Arrange
+        var mockDestinationProperty = new Mock<IPropertySymbol>();
+        var instruction = new TestPropertyMappingInstruction(mockDestinationProperty.Object);
+
+        // Assert
+        var property = typeof(PropertyMappingInstruction).GetProperty(nameof(PropertyMappingInstruction.DestinationProperty));
+        property!.CanWrite.Should().BeFalse();
+        property.CanRead.Should().BeTrue();
+    }
+
+    // Test implementation of abstract PropertyMappingInstruction
+    private class TestPropertyMappingInstruction : PropertyMappingInstruction
+    {
+        public TestPropertyMappingInstruction(IPropertySymbol destinationProperty) : base(destinationProperty) { }
+    }
+}