test: Add tests for CheckPdfAttachments feature

- Unit tests for CheckPdfAttachmentsQueryHandler (3 tests)
- Integration tests for PdfAttachmentController (14 tests covering both multipart and JSON endpoints)
- Tests verify: attachment detection, metadata extraction, empty PDF handling, validation errors
- All tests using Stream API (mocks with It.IsAny<Stream>())
- Total: 17 new tests, all passing

DocumentOperator.Tests/Unit/Application/CheckPdfAttachments/CheckPdfAttachmentsQueryHandlerTests.cs

@@ -0,0 +1,123 @@
+using AutoMapper;
+using DocumentOperator.Application.CheckPdfAttachments.Queries;
+using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Application.Common.Interfaces;
+
+using FluentAssertions;
+using Moq;
+
+namespace DocumentOperator.Tests.Unit.Application.CheckPdfAttachments;
+
+/// <summary>
+/// Unit tests for CheckPdfAttachmentsQueryHandler.
+/// Tests handler logic with mocked dependencies (IPdfProcessor, IMapper).
+/// </summary>
+public class CheckPdfAttachmentsQueryHandlerTests
+{
+    private readonly Mock<IPdfProcessor> _mockPdfProcessor;
+    private readonly Mock<IMapper> _mockMapper;
+    private readonly CheckPdfAttachmentsQueryHandler _sut;
+
+    public CheckPdfAttachmentsQueryHandlerTests()
+    {
+        _mockPdfProcessor = new Mock<IPdfProcessor>();
+        _mockMapper = new Mock<IMapper>();
+        _sut = new CheckPdfAttachmentsQueryHandler(_mockPdfProcessor.Object, _mockMapper.Object);
+    }
+
+    [Fact]
+    public async Task Handle_WithPdfBytes_CallsProcessorAndMapper()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+
+        var domainResult = new AttachmentInfo(
+            hasAttachments: true,
+            attachmentCount: 2,
+            attachments:
+            [
+                new("invoice.xml", "text/xml", 1024),
+                new("metadata.json", "application/json", 512)
+            ]
+        );
+
+        var expectedDto = new AttachmentCheckResult
+        {
+            HasAttachments = true,
+            AttachmentCount = 2,
+            Attachments =
+            [
+                new() { FileName = "invoice.xml", MimeType = "text/xml", Size = 1024 },
+                new() { FileName = "metadata.json", MimeType = "application/json", Size = 512 }
+            ]
+        };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().BeEquivalentTo(expectedDto);
+
+        _mockPdfProcessor.Verify(p => p.CheckAttachmentsAsync(It.IsAny<Stream>()), Times.Once);
+        _mockMapper.Verify(m => m.Map<AttachmentCheckResult>(domainResult), Times.Once);
+    }
+
+    [Fact]
+    public async Task Handle_WithBase64Pdf_DecodesAndCallsProcessor()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        string base64Pdf = Convert.ToBase64String(pdfBytes);
+        var query = new CheckPdfAttachmentsQuery { Base64Pdf = base64Pdf };
+
+        var domainResult = new AttachmentInfo(false, 0, []);
+        var expectedDto = new AttachmentCheckResult { HasAttachments = false, AttachmentCount = 0, Attachments = [] };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+
+        _mockPdfProcessor.Verify(p => p.CheckAttachmentsAsync(It.IsAny<Stream>()), Times.Once);
+    }
+
+    [Fact]
+    public async Task Handle_WithEmptyAttachments_ReturnsEmptyList()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+
+        var domainResult = new AttachmentInfo(false, 0, []);
+        var expectedDto = new AttachmentCheckResult
+        {
+            HasAttachments = false,
+            AttachmentCount = 0,
+            Attachments = []
+        };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+        result.Attachments.Should().BeEmpty();
+    }
+}
+
+