Add additional unit tests for utils and EE (#3557)

## Summary
- add tests for LicenseKeyChecker
- expand GeneralUtils coverage
- cover extra PdfUtils functionality
- merge PdfUtilsMoreTest into PdfUtilsTest

## Testing
- `./gradlew test --no-daemon`
- `./gradlew build spotlessApply --no-daemon`

src/test/java/stirling/software/SPDF/EE/LicenseKeyCheckerTest.java

@@ -0,0 +1,77 @@
+package stirling.software.SPDF.EE;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.io.TempDir;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import stirling.software.SPDF.EE.KeygenLicenseVerifier.License;
+import stirling.software.SPDF.model.ApplicationProperties;
+
+@ExtendWith(MockitoExtension.class)
+class LicenseKeyCheckerTest {
+
+    @Mock private KeygenLicenseVerifier verifier;
+
+    @Test
+    void premiumDisabled_skipsVerification() {
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(false);
+        props.getPremium().setKey("dummy");
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.NORMAL, checker.getPremiumLicenseEnabledResult());
+        verifyNoInteractions(verifier);
+    }
+
+    @Test
+    void directKey_verified() {
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("abc");
+        when(verifier.verifyLicense("abc")).thenReturn(License.PRO);
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.PRO, checker.getPremiumLicenseEnabledResult());
+        verify(verifier).verifyLicense("abc");
+    }
+
+    @Test
+    void fileKey_verified(@TempDir Path temp) throws IOException {
+        Path file = temp.resolve("license.txt");
+        Files.writeString(file, "filekey");
+
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("file:" + file.toString());
+        when(verifier.verifyLicense("filekey")).thenReturn(License.ENTERPRISE);
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.ENTERPRISE, checker.getPremiumLicenseEnabledResult());
+        verify(verifier).verifyLicense("filekey");
+    }
+
+    @Test
+    void missingFile_resultsNormal(@TempDir Path temp) {
+        Path file = temp.resolve("missing.txt");
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("file:" + file.toString());
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.NORMAL, checker.getPremiumLicenseEnabledResult());
+        verifyNoInteractions(verifier);
+    }
+}

src/test/java/stirling/software/SPDF/utils/GeneralUtilsAdditionalTest.java

@@ -0,0 +1,41 @@
+package stirling.software.SPDF.utils;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class GeneralUtilsAdditionalTest {
+
+    @Test
+    void testConvertSizeToBytes() {
+        assertEquals(1024L, GeneralUtils.convertSizeToBytes("1KB"));
+        assertEquals(1024L * 1024, GeneralUtils.convertSizeToBytes("1MB"));
+        assertEquals(1024L * 1024 * 1024, GeneralUtils.convertSizeToBytes("1GB"));
+        assertEquals(100L * 1024 * 1024, GeneralUtils.convertSizeToBytes("100"));
+        assertNull(GeneralUtils.convertSizeToBytes("invalid"));
+        assertNull(GeneralUtils.convertSizeToBytes(null));
+    }
+
+    @Test
+    void testFormatBytes() {
+        assertEquals("512 B", GeneralUtils.formatBytes(512));
+        assertEquals("1.00 KB", GeneralUtils.formatBytes(1024));
+        assertEquals("1.00 MB", GeneralUtils.formatBytes(1024L * 1024));
+        assertEquals("1.00 GB", GeneralUtils.formatBytes(1024L * 1024 * 1024));
+    }
+
+    @Test
+    void testURLHelpersAndUUID() {
+        assertTrue(GeneralUtils.isValidURL("https://example.com"));
+        assertFalse(GeneralUtils.isValidURL("htp:/bad"));
+        assertFalse(GeneralUtils.isURLReachable("http://localhost"));
+        assertFalse(GeneralUtils.isURLReachable("ftp://example.com"));
+
+        assertTrue(GeneralUtils.isValidUUID("123e4567-e89b-12d3-a456-426614174000"));
+        assertFalse(GeneralUtils.isValidUUID("not-a-uuid"));
+
+        assertFalse(GeneralUtils.isVersionHigher(null, "1.0"));
+        assertTrue(GeneralUtils.isVersionHigher("2.0", "1.9"));
+        assertFalse(GeneralUtils.isVersionHigher("1.0", "1.0.1"));
+    }
+}

src/test/java/stirling/software/SPDF/utils/PdfUtilsTest.java

@@ -5,12 +5,17 @@ import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.awt.Color;
+import java.awt.Graphics2D;
+import java.awt.image.BufferedImage;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.apache.pdfbox.cos.COSName;
+import org.apache.pdfbox.pdmodel.PDDocument;
 import org.apache.pdfbox.pdmodel.PDPage;
 import org.apache.pdfbox.pdmodel.PDResources;
 import org.apache.pdfbox.pdmodel.common.PDRectangle;
@@ -18,6 +23,10 @@ import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
 
+import stirling.software.SPDF.model.ApplicationProperties;
+import stirling.software.SPDF.service.CustomPDFDocumentFactory;
+import stirling.software.SPDF.service.PdfMetadataService;
+
 public class PdfUtilsTest {
 
     @Test
@@ -49,4 +58,68 @@ public class PdfUtilsTest {
 
         assertTrue(PdfUtils.hasImagesOnPage(page));
     }
+
+    @Test
+    void testPageCountComparators() throws Exception {
+        PDDocument doc1 = new PDDocument();
+        doc1.addPage(new PDPage());
+        doc1.addPage(new PDPage());
+        doc1.addPage(new PDPage());
+        PdfUtils utils = new PdfUtils();
+        assertTrue(utils.pageCount(doc1, 2, "greater"));
+
+        PDDocument doc2 = new PDDocument();
+        doc2.addPage(new PDPage());
+        doc2.addPage(new PDPage());
+        doc2.addPage(new PDPage());
+        assertTrue(utils.pageCount(doc2, 3, "equal"));
+
+        PDDocument doc3 = new PDDocument();
+        doc3.addPage(new PDPage());
+        doc3.addPage(new PDPage());
+        assertTrue(utils.pageCount(doc3, 5, "less"));
+
+        PDDocument doc4 = new PDDocument();
+        doc4.addPage(new PDPage());
+        assertThrows(IllegalArgumentException.class, () -> utils.pageCount(doc4, 1, "bad"));
+    }
+
+    @Test
+    void testPageSize() throws Exception {
+        PDDocument doc = new PDDocument();
+        PDPage page = new PDPage(PDRectangle.A4);
+        doc.addPage(page);
+        PDRectangle rect = page.getMediaBox();
+        String expected = rect.getWidth() + "x" + rect.getHeight();
+        PdfUtils utils = new PdfUtils();
+        assertTrue(utils.pageSize(doc, expected));
+    }
+
+    @Test
+    void testOverlayImage() throws Exception {
+        PDDocument doc = new PDDocument();
+        doc.addPage(new PDPage(PDRectangle.A4));
+        ByteArrayOutputStream pdfOut = new ByteArrayOutputStream();
+        doc.save(pdfOut);
+        doc.close();
+
+        BufferedImage image = new BufferedImage(10, 10, BufferedImage.TYPE_INT_RGB);
+        Graphics2D g = image.createGraphics();
+        g.setColor(Color.RED);
+        g.fillRect(0, 0, 10, 10);
+        g.dispose();
+        ByteArrayOutputStream imgOut = new ByteArrayOutputStream();
+        javax.imageio.ImageIO.write(image, "png", imgOut);
+
+        PdfMetadataService meta =
+                new PdfMetadataService(new ApplicationProperties(), "label", false, null);
+        CustomPDFDocumentFactory factory = new CustomPDFDocumentFactory(meta);
+
+        byte[] result =
+                PdfUtils.overlayImage(
+                        factory, pdfOut.toByteArray(), imgOut.toByteArray(), 0, 0, false);
+        try (PDDocument resultDoc = factory.load(result)) {
+            assertEquals(1, resultDoc.getNumberOfPages());
+        }
+    }
 }