feat: add JUnit tests for EML to PDF conversion (#3806)

# Description of Changes This PR introduces tests for EML-to-PDF feature, but indirectly tests also HTML-to-PDF as well as Attachments feature. - Adds JUnit tests for EML-to-PDF conversion, including scenarios with file attachments, multipart, complex, CSS styled etc.. emails. - Confirms that adding Angus Mail as a runtime dependency does not introduce any issues or regressions. PR is relevant after #3781 --- ## Checklist ### General - [x] I have read the [Contribution Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md) - [x] I have read the [Stirling-PDF Developer Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md) (if applicable) - [ ] I have read the [How to add new languages to Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md) (if applicable) - [x] I have performed a self-review of my own code - [x] My changes generate no new warnings ### Documentation - [ ] I have updated relevant docs on [Stirling-PDF's doc repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/) (if functionality has heavily changed) - [ ] I have read the section [Add New Translation Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags) (for new translation tags only) ### UI Changes (if applicable) - [ ] Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR) ### Testing (if applicable) - [x] I have tested my changes locally. Refer to the [Testing Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing) for more details.
2025-07-23 13:45:21 +00:00 · 2025-06-25 19:33:50 +02:00 · 2025-06-25 19:33:50 +02:00 · 6461b93131
commit 6461b93131
parent bc9c127819
1 changed files with 883 additions and 0 deletions
--- a/common/src/test/java/stirling/software/common/util/EmlToPdfTest.java
+++ b/common/src/test/java/stirling/software/common/util/EmlToPdfTest.java
@ -0,0 +1,883 @@
+package stirling.software.common.util;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Base64;
+
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.pdmodel.PDPage;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.ArgumentMatchers.anyString;
+import org.mockito.Mock;
+import org.mockito.MockedStatic;
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import stirling.software.common.model.api.converters.EmlToPdfRequest;
+import stirling.software.common.service.CustomPDFDocumentFactory;
+
+@DisplayName("EML to PDF Conversion tests")
+class EmlToPdfTest {
+
+    // Focus on testing EML to HTML conversion functionality since the PDF conversion relies on WeasyPrint
+    // But HTML to PDF conversion is also briefly tested at PdfConversionTests class.
+    private void testEmailConversion(String emlContent, String[] expectedContent, boolean includeAttachments) throws IOException {
+        byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+        EmlToPdfRequest request = includeAttachments ? createRequestWithAttachments() : createBasicRequest();
+
+        String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+        assertNotNull(htmlResult);
+        for (String expected : expectedContent) {
+            assertTrue(htmlResult.contains(expected), "HTML should contain: " + expected);
+        }
+    }
+
+    @Nested
+    @DisplayName("Core EML Parsing")
+    class CoreParsingTests {
+        @Test
+        @DisplayName("Should parse simple text email correctly")
+        void parseSimpleTextEmail() throws IOException {
+            String emlContent = createSimpleTextEmail(
+                "sender@example.com",
+                "recipient@example.com",
+                "Simple Test Subject",
+                "This is a simple plain text email body.");
+
+            testEmailConversion(emlContent, new String[] {
+                "Simple Test Subject",
+                "sender@example.com",
+                "recipient@example.com",
+                "This is a simple plain text email body",
+                "<!DOCTYPE html>"
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should parse email with missing Subject and To headers")
+        void parseEmailWithMissingHeaders() throws IOException {
+            String emlContent = createEmailWithCustomHeaders();
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains("sender@example.com"));
+            assertTrue(htmlResult.contains("This is an email body"));
+            assertTrue(htmlResult.contains("<title></title>") ||
+                htmlResult.contains("<title>No Subject</title>"));
+        }
+
+        @Test
+        @DisplayName("Should parse HTML email with styling")
+        void parseHtmlEmailWithStyling() throws IOException {
+            String htmlBody = "<html><head><style>.header{color:blue;font-weight:bold;}" +
+                ".content{margin:10px;}.footer{font-size:12px;}</style></head>" +
+                "<body><div class=\"header\">Important Notice</div>" +
+                "<div class=\"content\">This is <strong>HTML content</strong> with styling.</div>" +
+                "<div class=\"footer\">Best regards</div></body></html>";
+
+            String emlContent = createHtmlEmail(
+                "html@example.com", "user@example.com", "HTML Email Test", htmlBody);
+
+            testEmailConversion(emlContent, new String[] {
+                "HTML Email Test",
+                "Important Notice",
+                "HTML content",
+                "font-weight: bold"
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should parse multipart email with attachments")
+        void parseMultipartEmailWithAttachments() throws IOException {
+            String boundary = "----=_Part_" + getTimestamp();
+            String emlContent = createMultipartEmailWithAttachment(
+                "multipart@example.com",
+                "user@example.com",
+                "Multipart Email Test",
+                "This email has both text content and an attachment.",
+                boundary,
+                "document.txt",
+                "Sample attachment content");
+
+            testEmailConversion(emlContent, new String[] {
+                "Multipart Email Test",
+                "This email has both text content"
+            }, true);
+        }
+    }
+
+    @Nested
+    @DisplayName("Email Encoding Support")
+    class EncodingTests {
+
+        @Test
+        @DisplayName("Should handle international characters and UTF-8")
+        void handleInternationalCharacters() throws IOException {
+            String bodyWithIntlChars = "Hello! 你好 Привет مرحبا Hëllö Thañks! Önë Mörë";
+            String emlContent = createSimpleTextEmail(
+                "intl@example.com",
+                "user@example.com",
+                "International Characters Test",
+                bodyWithIntlChars);
+
+            testEmailConversion(emlContent, new String[] {
+                "你好", "Привет", "مرحبا", "Hëllö", "Önë", "Mörë"
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should decode quoted-printable content correctly")
+        void decodeQuotedPrintableContent() throws IOException {
+            String content = createQuotedPrintableEmail(
+            );
+
+            testEmailConversion(content, new String[] {
+                "Quoted-Printable Test",
+                "This is quoted printable content with special chars: éàè."
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should decode Base64 content")
+        void decodeBase64Content() throws IOException {
+            String originalText = "This is Base64 encoded content: éàü ñ";
+            String content = createBase64Email(
+                originalText);
+
+            testEmailConversion(content, new String[] {
+                "Base64 Test", "Base64 encoded content"
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should correctly handle inline images with CID references")
+        void handleInlineImages() throws IOException {
+            String boundary = "----=_Part_CID_1234567890";
+            String cid = "image123@example.com";
+            String htmlBody = "<html><body><p>Here is an image:</p><img src=\"cid:" + cid + "\"></body></html>";
+            String imageBase64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNkYPhfDwAChwGA60e6kgAAAABJRU5ErkJggg==";
+
+            String emlContent = createEmailWithInlineImage(htmlBody, boundary, cid, imageBase64);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createRequestWithAttachments();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains("data:image/png;base64," + imageBase64));
+            assertFalse(htmlResult.contains("cid:" + cid));
+        }
+    }
+
+    @Nested
+    @DisplayName("HTML Output Quality")
+    class HtmlOutputTests {
+
+        @Test
+        @DisplayName("Should generate valid HTML structure")
+        void generateValidHtmlStructure() throws IOException {
+            String emlContent = createSimpleTextEmail(
+                "structure@test.com",
+                "user@test.com",
+                "HTML Structure Test",
+                "Testing HTML structure output");
+
+            testEmailConversion(emlContent, new String[] {
+                "<!DOCTYPE html>", "<html", "</html>", "HTML Structure Test"
+            }, false);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, createBasicRequest());
+            assertTrue(htmlResult.length() > 100, "HTML should have substantial content");
+        }
+
+        @Test
+        @DisplayName("Should preserve safe CSS and remove problematic styles")
+        void handleCssStylesCorrectly() throws IOException {
+            String styledHtml = "<html><head><style>" +
+                ".safe { color: blue; font-size: 14px; }" +
+                ".problematic { position: fixed; word-break: break-all; }" +
+                ".good { margin: 10px; padding: 5px; }" +
+                "</style></head><body>" +
+                "<div class=\"safe\">Safe styling</div>" +
+                "<div class=\"problematic\">Problematic styling</div>" +
+                "<div class=\"good\">Good styling</div>" +
+                "</body></html>";
+
+            String emlContent = createHtmlEmail("css@test.com", "user@test.com", "CSS Test", styledHtml);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains("color: blue"));
+            assertTrue(htmlResult.contains("font-size: 14px"));
+            assertTrue(htmlResult.contains("margin: 10px"));
+
+            assertFalse(htmlResult.contains("position: fixed"));
+        }
+
+        @Test
+        @DisplayName("Should handle complex nested HTML structures")
+        void handleComplexNestedHtml() throws IOException {
+            String complexHtml = "<html><head><title>Complex Email</title></head><body>" +
+                "<div class=\"container\"><header><h1>Email Header</h1></header><main><section>" +
+                "<p>Paragraph with <a href=\"https://example.com\">link</a></p><ul>" +
+                "<li>List item 1</li><li>List item 2 with <em>emphasis</em></li></ul><table>" +
+                "<tr><td>Cell 1</td><td>Cell 2</td></tr><tr><td>Cell 3</td><td>Cell 4</td></tr>" +
+                "</table></section></main></div></body></html>";
+
+            String emlContent = createHtmlEmail(
+                "complex@test.com", "user@test.com", "Complex HTML Test", complexHtml);
+
+            testEmailConversion(emlContent, new String[] {
+                "Email Header", "List item 2", "Cell 3", "example.com"
+            }, false);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, createBasicRequest());
+            assertTrue(htmlResult.length() > 300, "HTML should have substantial content");
+        }
+    }
+
+    @Nested
+    @DisplayName("Error Handling & Edge Cases")
+    class ErrorHandlingTests {
+
+        @Test
+        @DisplayName("Should reject null input")
+        void rejectNullInput() {
+            EmlToPdfRequest request = createBasicRequest();
+
+            Exception exception = assertThrows(
+                IllegalArgumentException.class,
+                () -> EmlToPdf.convertEmlToHtml(null, request));
+            assertTrue(exception.getMessage().contains("EML file is empty or null"));
+        }
+
+        @Test
+        @DisplayName("Should reject empty input")
+        void rejectEmptyInput() {
+            EmlToPdfRequest request = createBasicRequest();
+
+            Exception exception = assertThrows(
+                IllegalArgumentException.class,
+                () -> EmlToPdf.convertEmlToHtml(new byte[0], request));
+            assertTrue(exception.getMessage().contains("EML file is empty or null"));
+        }
+
+        @Test
+        @DisplayName("Should handle malformed EML gracefully")
+        void handleMalformedEmlGracefully() {
+            String malformedEml = """
+                    From: sender@test.com
+                    Subject: Malformed EML
+                    This line breaks header format
+                    Content-Type: text/plain
+
+                    Body content""";
+
+            byte[] emlBytes = malformedEml.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+
+            try {
+                String result = EmlToPdf.convertEmlToHtml(emlBytes, request);
+                assertNotNull(result, "Result should not be null");
+                assertFalse(result.isEmpty(), "Result should not be empty");
+            } catch (Exception e) {
+                assertNotNull(e.getMessage(), "Exception message should not be null");
+                assertFalse(e.getMessage().isEmpty(), "Exception message should not be empty");
+            }
+        }
+
+        @Test
+        @DisplayName("Should reject invalid EML format")
+        void rejectInvalidEmlFormat() {
+            byte[] invalidEml = "This is definitely not an EML file".getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+
+            Exception exception = assertThrows(
+                IllegalArgumentException.class,
+                () -> EmlToPdf.convertEmlToHtml(invalidEml, request));
+            assertTrue(exception.getMessage().contains("Invalid EML file format"));
+        }
+    }
+
+    @Nested
+    @DisplayName("Advanced Parsing Tests (Jakarta Mail)")
+    class AdvancedParsingTests {
+
+        @Test
+        @DisplayName("Should successfully parse email using advanced parser")
+        void initializeDependencyMailSession() {
+            assertDoesNotThrow(() -> {
+                String emlContent = createSimpleTextEmail(
+                    "Dependency@test.com",
+                    "user@test.com",
+                    "Dependency Mail Test",
+                    "Testing Dependency Mail integration.");
+
+                byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+                EmlToPdfRequest request = createBasicRequest();
+
+                String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+                assertNotNull(htmlResult);
+                assertTrue(htmlResult.contains("Dependency Mail Test"));
+            });
+        }
+
+        @Test
+        @DisplayName("Should parse complex MIME structures and select HTML part")
+        void parseComplexMimeStructures() throws IOException {
+            String boundary = "----=_Advanced_1234567890";
+            String textBody = "This is the plain text part.";
+            String htmlBody = "<html><body><h1>This is the HTML part</h1></body></html>";
+            String emlContent = createMultipartAlternativeEmail(textBody, htmlBody, boundary);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createRequestWithAttachments();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains("This is the HTML part"));
+            assertFalse(htmlResult.contains("This is the plain text part"));
+        }
+    }
+
+    @Nested
+    @DisplayName("Additional Correctness Tests")
+    class AdditionalCorrectnessTests {
+
+        @Test
+        @DisplayName("Should handle email with only an attachment and no body")
+        void handleAttachmentOnlyEmail() throws IOException {
+            String boundary = "----=_Part_AttachmentOnly_1234567890";
+            String emlContent = createMultipartEmailWithAttachment(
+                "sender@example.com",
+                "recipient@example.com",
+                "Attachment Only Test",
+                "",
+                boundary,
+                "data.bin",
+                "binary data");
+
+            testEmailConversion(emlContent, new String[] {
+                "Attachment Only Test", "data.bin", "No content available"
+            }, true);
+        }
+
+        @Test
+        @DisplayName("Should handle mixed inline and regular attachments")
+        void handleMixedAttachments() throws IOException {
+            String boundary = "----=_Part_MixedAttachments_1234567890";
+            String cid = "inline_image@example.com";
+            String htmlBody = "<html><body><img src=\"cid:" + cid + "\"></body></html>";
+            String imageBase64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAACklEQVR42mNkAAIAAAoAAb6A/yoAAAAASUVORK5CYII=";
+            String attachmentText = "This is a text attachment.";
+
+            String emlContent = createEmailWithMixedAttachments(
+                htmlBody, boundary, cid, imageBase64, attachmentText);
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createRequestWithAttachments();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains("data:image/png;base64," + imageBase64));
+            assertTrue(htmlResult.contains("text.txt"));
+        }
+
+        @Test
+        @DisplayName("Should handle non-standard but valid character sets like ISO-8859-1")
+        void handleIso88591Charset() throws IOException {
+            String subject = "Subject with special characters: ñ é ü";
+            String body = "Body with special characters: ñ é ü";
+
+            String emlContent = createSimpleTextEmailWithCharset(
+                "sender@example.com",
+                "recipient@example.com",
+                subject,
+                body,
+                "ISO-8859-1");
+
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.ISO_8859_1);
+            EmlToPdfRequest request = createBasicRequest();
+
+            String htmlResult = EmlToPdf.convertEmlToHtml(emlBytes, request);
+
+            assertNotNull(htmlResult);
+            assertTrue(htmlResult.contains(subject));
+            assertTrue(htmlResult.contains(body));
+        }
+
+        @Test
+        @DisplayName("Should handle emails with extremely long lines")
+        void handleLongLines() throws IOException {
+            StringBuilder longLine = new StringBuilder("This is a very long line: ");
+            for (int i = 0; i < 1000; i++) {
+                longLine.append("word").append(i).append(" ");
+            }
+
+            String emlContent = createSimpleTextEmail(
+                "sender@example.com",
+                "recipient@example.com",
+                "Long Line Test",
+                longLine.toString());
+
+            testEmailConversion(emlContent, new String[] {
+                "Long Line Test", "This is a very long line", "word999"
+            }, false);
+        }
+
+        @Test
+        @DisplayName("Should handle .eml files as attachments")
+        void handleEmlAttachment() throws IOException {
+            String boundary = "----=_Part_EmlAttachment_1234567890";
+            String innerEmlContent = createSimpleTextEmail(
+                "inner@example.com",
+                "inner_recipient@example.com",
+                "Inner Email Subject",
+                "This is the body of the attached email.");
+
+            String emlContent = createEmailWithEmlAttachment(
+                boundary,
+                innerEmlContent);
+
+            testEmailConversion(emlContent, new String[] {
+                "Fwd: Inner Email Subject",
+                "Please see the attached email.",
+                "attached_email.eml"
+            }, true);
+        }
+
+        @ParameterizedTest
+        @ValueSource(strings = {"windows-1252", "ISO-8859-2", "KOI8-R", "Shift_JIS"})
+        @DisplayName("Should handle various character encodings")
+        void handleVariousEncodings(String charset) throws IOException {
+            String subject = "Encoding Test";
+            String body = "Testing " + charset + " encoding";
+
+            String emlContent = createSimpleTextEmailWithCharset(
+                "sender@example.com",
+                "recipient@example.com",
+                subject,
+                body,
+                charset);
+
+            testEmailConversion(emlContent, new String[] {subject, body}, false);
+        }
+    }
+
+    @Nested
+    @ExtendWith(MockitoExtension.class)
+    @DisplayName("PDF Conversion Tests")
+    class PdfConversionTests {
+
+        @Mock private CustomPDFDocumentFactory mockPdfDocumentFactory;
+
+        @Mock private PDDocument mockPdDocument;
+
+        @Test
+        @DisplayName("Should convert EML to PDF without attachments when not requested")
+        void convertEmlToPdfWithoutAttachments() throws Exception {
+            String emlContent =
+                createSimpleTextEmail("from@test.com", "to@test.com", "Subject", "Body");
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+
+            PDDocument testPdf = new PDDocument();
+            testPdf.addPage(new PDPage());
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            testPdf.save(baos);
+            testPdf.close();
+            byte[] fakePdfBytes = baos.toByteArray();
+
+            when(mockPdfDocumentFactory.load(any(byte[].class))).thenReturn(mockPdDocument);
+            when(mockPdDocument.getNumberOfPages()).thenReturn(1);
+
+            try (MockedStatic<FileToPdf> fileToPdf = mockStatic(FileToPdf.class)) {
+                fileToPdf
+                    .when(
+                        () ->
+                            FileToPdf.convertHtmlToPdf(
+                                anyString(),
+                                any(),
+                                any(byte[].class),
+                                anyString(),
+                                anyBoolean()))
+                    .thenReturn(fakePdfBytes);
+
+                byte[] resultPdf =
+                    EmlToPdf.convertEmlToPdf(
+                        "weasyprint",
+                        request,
+                        emlBytes,
+                        "test.eml",
+                        false,
+                        mockPdfDocumentFactory);
+
+                assertArrayEquals(fakePdfBytes, resultPdf);
+
+                try (PDDocument resultDoc = mockPdfDocumentFactory.load(resultPdf)) {
+                    assertNotNull(resultDoc);
+                    assertTrue(resultDoc.getNumberOfPages() > 0);
+                }
+
+                fileToPdf.verify(
+                    () ->
+                        FileToPdf.convertHtmlToPdf(
+                            anyString(),
+                            any(),
+                            any(byte[].class),
+                            anyString(),
+                            anyBoolean()));
+                verify(mockPdfDocumentFactory).load(resultPdf);
+            }
+        }
+
+        @Test
+        @DisplayName("Should convert EML to PDF with attachments when requested")
+        void convertEmlToPdfWithAttachments() throws Exception {
+            String boundary = "----=_Part_1234567890";
+            String emlContent = createMultipartEmailWithAttachment(
+                "multipart@example.com",
+                "user@example.com",
+                "Multipart Email Test",
+                "This email has both text content and an attachment.",
+                boundary,
+                "document.txt",
+                "Sample attachment content");
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createRequestWithAttachments();
+
+            PDDocument testPdf = new PDDocument();
+            testPdf.addPage(new PDPage());
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            testPdf.save(baos);
+            testPdf.close();
+            byte[] fakePdfBytes = baos.toByteArray();
+
+            when(mockPdfDocumentFactory.load(any(byte[].class))).thenReturn(mockPdDocument);
+            when(mockPdDocument.getNumberOfPages()).thenReturn(1);
+
+            try (MockedStatic<FileToPdf> fileToPdf = mockStatic(FileToPdf.class)) {
+                fileToPdf
+                    .when(
+                        () ->
+                            FileToPdf.convertHtmlToPdf(
+                                anyString(),
+                                any(),
+                                any(byte[].class),
+                                anyString(),
+                                anyBoolean()))
+                    .thenReturn(fakePdfBytes);
+
+                try (MockedStatic<EmlToPdf> ignored =
+                         mockStatic(
+                             EmlToPdf.class,
+                             invocation -> {
+                                 String methodName = invocation.getMethod().getName();
+                                 return switch (methodName) {
+                                     case "shouldAttachFiles" -> true;
+                                     case "attachFilesToPdf" -> fakePdfBytes;
+                                     default -> invocation.callRealMethod();
+                                 };
+                             })) {
+                    byte[] resultPdf =
+                        EmlToPdf.convertEmlToPdf(
+                            "weasyprint",
+                            request,
+                            emlBytes,
+                            "test.eml",
+                            false,
+                            mockPdfDocumentFactory);
+
+                    assertArrayEquals(fakePdfBytes, resultPdf);
+
+                    try (PDDocument resultDoc = mockPdfDocumentFactory.load(resultPdf)) {
+                        assertNotNull(resultDoc);
+                        assertTrue(resultDoc.getNumberOfPages() > 0);
+                    }
+
+                    fileToPdf.verify(
+                        () ->
+                            FileToPdf.convertHtmlToPdf(
+                                anyString(),
+                                any(),
+                                any(byte[].class),
+                                anyString(),
+                                anyBoolean()));
+
+                    verify(mockPdfDocumentFactory).load(resultPdf);
+                }
+            }
+        }
+
+        @Test
+        @DisplayName("Should handle errors during EML to PDF conversion")
+        void handleErrorsDuringConversion() {
+            String emlContent =
+                createSimpleTextEmail("from@test.com", "to@test.com", "Subject", "Body");
+            byte[] emlBytes = emlContent.getBytes(StandardCharsets.UTF_8);
+            EmlToPdfRequest request = createBasicRequest();
+            String errorMessage = "Conversion failed";
+
+            try (MockedStatic<FileToPdf> fileToPdf = mockStatic(FileToPdf.class)) {
+                fileToPdf
+                    .when(
+                        () ->
+                            FileToPdf.convertHtmlToPdf(
+                                anyString(),
+                                any(),
+                                any(byte[].class),
+                                anyString(),
+                                anyBoolean()))
+                    .thenThrow(new IOException(errorMessage));
+
+                IOException exception = assertThrows(
+                    IOException.class,
+                    () -> EmlToPdf.convertEmlToPdf(
+                        "weasyprint",
+                        request,
+                        emlBytes,
+                        "test.eml",
+                        false,
+                        mockPdfDocumentFactory));
+
+                assertTrue(exception.getMessage().contains(errorMessage));
+            }
+        }
+    }
+
+    // Helper methods
+    private String getTimestamp() {
+        java.time.ZonedDateTime fixedDateTime = java.time.ZonedDateTime.of(2023, 1, 1, 12, 0, 0, 0, java.time.ZoneId.of("GMT"));
+        return java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME.format(fixedDateTime);
+    }
+    private String createSimpleTextEmail(String from, String to, String subject, String body) {
+        return createSimpleTextEmailWithCharset(from, to, subject, body, "UTF-8");
+    }
+
+    private String createSimpleTextEmailWithCharset(String from, String to, String subject, String body, String charset) {
+        return String.format(
+            "From: %s\nTo: %s\nSubject: %s\nDate: %s\nContent-Type: text/plain; charset=%s\nContent-Transfer-Encoding: 8bit\n\n%s",
+            from, to, subject, getTimestamp(), charset, body);
+    }
+
+    private String createEmailWithCustomHeaders() {
+        return String.format(
+            "From: sender@example.com\nDate: %s\nContent-Type: text/plain; charset=UTF-8\nContent-Transfer-Encoding: 8bit\n\n%s",
+            getTimestamp(), "This is an email body with some headers missing.");
+    }
+
+    private String createHtmlEmail(String from, String to, String subject, String htmlBody) {
+        return String.format(
+            "From: %s\nTo: %s\nSubject: %s\nDate: %s\nContent-Type: text/html; charset=UTF-8\nContent-Transfer-Encoding: 8bit\n\n%s",
+            from, to, subject, getTimestamp(), htmlBody);
+    }
+
+    private String createMultipartEmailWithAttachment(String from, String to, String subject, String body,
+                                                      String boundary, String filename, String attachmentContent) {
+        String encodedContent = Base64.getEncoder().encodeToString(attachmentContent.getBytes(StandardCharsets.UTF_8));
+        return String.format(
+            """
+                    From: %s
+                    To: %s
+                    Subject: %s
+                    Date: %s
+                    Content-Type: multipart/mixed; boundary="%s"
+
+                    --%s
+                    Content-Type: text/plain; charset=UTF-8
+                    Content-Transfer-Encoding: 8bit
+
+                    %s
+
+                    --%s
+                    Content-Type: text/plain; charset=UTF-8
+                    Content-Disposition: attachment; filename="%s"
+                    Content-Transfer-Encoding: base64
+
+                    %s
+
+                    --%s--""",
+            from, to, subject, getTimestamp(), boundary, boundary, body, boundary, filename, encodedContent, boundary);
+    }
+
+    private String createEmailWithEmlAttachment(String boundary, String attachmentEmlContent) {
+        String encodedContent = Base64.getEncoder().encodeToString(attachmentEmlContent.getBytes(StandardCharsets.UTF_8));
+        return String.format(
+            """
+                    From: %s
+                    To: %s
+                    Subject: %s
+                    Date: %s
+                    Content-Type: multipart/mixed; boundary="%s"
+
+                    --%s
+                    Content-Type: text/plain; charset=UTF-8
+                    Content-Transfer-Encoding: 8bit
+
+                    %s
+
+                    --%s
+                    Content-Type: message/rfc822; name="%s"
+                    Content-Disposition: attachment; filename="%s"
+                    Content-Transfer-Encoding: base64
+
+                    %s
+
+                    --%s--""",
+            "outer@example.com", "outer_recipient@example.com", "Fwd: Inner Email Subject", getTimestamp(), boundary, boundary, "Please see the attached email.", boundary, "attached_email.eml", "attached_email.eml", encodedContent, boundary);
+    }
+
+    private String createMultipartAlternativeEmail(String textBody, String htmlBody, String boundary) {
+        return String.format(
+            """
+                    From: %s
+                    To: %s
+                    Subject: %s
+                    Date: %s
+                    MIME-Version: 1.0
+                    Content-Type: multipart/alternative; boundary="%s"
+
+                    --%s
+                    Content-Type: text/plain; charset=UTF-8
+                    Content-Transfer-Encoding: 7bit
+
+                    %s
+
+                    --%s
+                    Content-Type: text/html; charset=UTF-8
+                    Content-Transfer-Encoding: 7bit
+
+                    %s
+
+                    --%s--""",
+            "sender@example.com", "receiver@example.com", "Multipart/Alternative Test", getTimestamp(),
+            boundary, boundary, textBody, boundary, htmlBody, boundary);
+    }
+
+    private String createQuotedPrintableEmail() {
+        return String.format(
+            "From: %s\nTo: %s\nSubject: %s\nDate: %s\nMIME-Version: 1.0\nContent-Type: text/plain; charset=UTF-8\nContent-Transfer-Encoding: quoted-printable\n\n%s",
+            "sender@example.com", "recipient@example.com", "Quoted-Printable Test", getTimestamp(), "This is quoted=20printable content with special chars: =C3=A9=C3=A0=C3=A8.");
+    }
+
+    private String createBase64Email(String body) {
+        String encodedBody = Base64.getEncoder().encodeToString(body.getBytes(StandardCharsets.UTF_8));
+        return String.format(
+            "From: %s\nTo: %s\nSubject: %s\nDate: %s\nMIME-Version: 1.0\nContent-Type: text/plain; charset=UTF-8\nContent-Transfer-Encoding: base64\n\n%s",
+            "sender@example.com", "recipient@example.com", "Base64 Test", getTimestamp(), encodedBody);
+    }
+
+    private String createEmailWithInlineImage(String htmlBody, String boundary, String contentId, String base64Image) {
+        return String.format(
+            """
+                    From: %s
+                    To: %s
+                    Subject: %s
+                    Date: %s
+                    Content-Type: multipart/related; boundary="%s"
+
+                    --%s
+                    Content-Type: text/html; charset=UTF-8
+                    Content-Transfer-Encoding: 8bit
+
+                    %s
+
+                    --%s
+                    Content-Type: image/png
+                    Content-Transfer-Encoding: base64
+                    Content-ID: <%s>
+                    Content-Disposition: inline; filename="image.png"
+
+                    %s
+
+                    --%s--""",
+            "sender@example.com", "receiver@example.com", "Inline Image Test", getTimestamp(),
+            boundary, boundary, htmlBody, boundary, contentId, base64Image, boundary);
+    }
+
+    private String createEmailWithMixedAttachments(String htmlBody, String boundary, String contentId,
+                                                   String base64Image, String attachmentBody) {
+        String encodedAttachment = Base64.getEncoder().encodeToString(attachmentBody.getBytes(StandardCharsets.UTF_8));
+        return String.format(
+            """
+                    From: %s
+                    To: %s
+                    Subject: %s
+                    Date: %s
+                    Content-Type: multipart/mixed; boundary="%s"
+
+                    --%s
+                    Content-Type: multipart/related; boundary="related-%s"
+
+                    --related-%s
+                    Content-Type: text/html; charset=UTF-8
+                    Content-Transfer-Encoding: 8bit
+
+                    %s
+
+                    --related-%s
+                    Content-Type: image/png
+                    Content-Transfer-Encoding: base64
+                    Content-ID: <%s>
+                    Content-Disposition: inline; filename="image.png"
+
+                    %s
+
+                    --related-%s--
+
+                    --%s
+                    Content-Type: text/plain; charset=UTF-8
+                    Content-Disposition: attachment; filename="%s"
+                    Content-Transfer-Encoding: base64
+
+                    %s
+
+                    --%s--""",
+            "sender@example.com", "receiver@example.com", "Mixed Attachments Test", getTimestamp(),
+            boundary, boundary, boundary, boundary, htmlBody, boundary, contentId, base64Image, boundary,
+            boundary, "text.txt", encodedAttachment, boundary);
+    }
+    // Creates a basic EmlToPdfRequest with default settings
+    private EmlToPdfRequest createBasicRequest() {
+        EmlToPdfRequest request = new EmlToPdfRequest();
+        request.setIncludeAttachments(false);
+        return request;
+    }
+
+    private EmlToPdfRequest createRequestWithAttachments() {
+        EmlToPdfRequest request = new EmlToPdfRequest();
+        request.setIncludeAttachments(true);
+        request.setMaxAttachmentSizeMB(10);
+        return request;
+    }
+}