Add JUnit tests for common and core module coverage (Stirling-Tools#6675)

# Description of Changes

JUNITS!
They JUnits were 100% AI generated however no code was touched

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] 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/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] 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/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### 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)

- [ ] I have run `task check` to verify linters, typechecks, and tests
pass
- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#7-testing)
for more details.

Author: Frooodle

app/common/src/test/java/stirling/software/SPDF/config/EndpointConfigurationGapTest.java

@@ -0,0 +1,345 @@
+package stirling.software.SPDF.pdf.parser;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static stirling.software.SPDF.pdf.parser.PdfModels.RawPage;
+import static stirling.software.SPDF.pdf.parser.PdfModels.TableCell;
+import static stirling.software.SPDF.pdf.parser.PdfModels.TableFragment;
+import static stirling.software.SPDF.pdf.parser.PdfModels.TableRow;
+
+import java.awt.Color;
+import java.io.ByteArrayOutputStream;
+import java.util.List;
+
+import org.apache.pdfbox.Loader;
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.pdmodel.PDPage;
+import org.apache.pdfbox.pdmodel.PDPageContentStream;
+import org.apache.pdfbox.pdmodel.common.PDRectangle;
+import org.apache.pdfbox.pdmodel.font.PDType1Font;
+import org.apache.pdfbox.pdmodel.font.Standard14Fonts;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link TabulaTableParser}. Tables are built in-memory with PDFBox so the tests are
+ * deterministic and need no fixtures, network, or external processes.
+ */
+class TabulaTableParserGapTest {
+
+    private final TabulaTableParser parser = new TabulaTableParser();
+
+    // ── error / empty branches ───────────────────────────────────────────────
+
+    @Nested
+    @DisplayName("Empty and error branches")
+    class EmptyAndErrorBranches {
+
+        @Test
+        @DisplayName("page number 0 is out of Tabula's 1-based range -> empty list, no throw")
+        void pageNumberZeroReturnsEmpty() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"hello"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> result = parser.parse(doc, 0);
+                assertNotNull(result);
+                assertTrue(result.isEmpty());
+            }
+        }
+
+        @Test
+        @DisplayName("page number beyond the document -> empty list, exception swallowed")
+        void pageNumberOutOfRangeReturnsEmpty() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"hello"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> result = parser.parse(doc, 99);
+                assertNotNull(result);
+                assertTrue(result.isEmpty());
+            }
+        }
+
+        @Test
+        @DisplayName("negative page number -> empty list")
+        void negativePageNumberReturnsEmpty() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"hello"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                assertTrue(parser.parse(doc, -5).isEmpty());
+            }
+        }
+
+        @Test
+        @DisplayName("lattice mode on a page with no ruled lines -> no tables")
+        void latticeWithNoRulingsReturnsEmpty() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"just some prose", "no table here"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> result = parser.parse(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertNotNull(result);
+                assertTrue(
+                        result.isEmpty(), "borderless text must not be detected in lattice mode");
+            }
+        }
+
+        @Test
+        @DisplayName("blank page in lattice mode -> empty list")
+        void blankPageLatticeReturnsEmpty() throws Exception {
+            byte[] pdf = blankPdf();
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                assertTrue(parser.parse(doc, new RawPage(1, 0f, 0f, List.of())).isEmpty());
+            }
+        }
+    }
+
+    // ── stream mode (BasicExtractionAlgorithm) ───────────────────────────────
+
+    @Nested
+    @DisplayName("Stream mode")
+    class StreamMode {
+
+        @Test
+        @DisplayName("page with text yields at least one well-formed fragment")
+        void streamOnTextProducesFragment() throws Exception {
+            byte[] pdf =
+                    pdfWithText(new String[] {"Name Age City", "Alice 30 Paris", "Bob 25 Rome"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments =
+                        parser.parseStream(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertNotNull(fragments);
+                assertFalse(fragments.isEmpty(), "stream mode always builds a table from text");
+                assertFragmentWellFormed(fragments.get(0), 1, 0);
+            }
+        }
+
+        @Test
+        @DisplayName("fragment ids encode page and index")
+        void streamFragmentIdFormat() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"col1 col2", "a b"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments =
+                        parser.parseStream(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertFalse(fragments.isEmpty());
+                assertEquals("tbl-p1-0", fragments.get(0).tableId());
+                assertEquals(1, fragments.get(0).pageNumber());
+            }
+        }
+
+        @Test
+        @DisplayName("rawRows and the parsed rows stay in lockstep")
+        void streamRowsMatchRawRows() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"x y", "1 2", "3 4"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments =
+                        parser.parseStream(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertFalse(fragments.isEmpty());
+                TableFragment f = fragments.get(0);
+                assertEquals(f.rawRows().size(), f.rows().size());
+            }
+        }
+    }
+
+    // ── lattice mode with a real bordered grid ───────────────────────────────
+
+    @Nested
+    @DisplayName("Lattice mode")
+    class LatticeMode {
+
+        @Test
+        @DisplayName("bordered grid is detected and produces well-formed fragments")
+        void latticeDetectsBorderedTable() throws Exception {
+            byte[] pdf = pdfWithGrid();
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments =
+                        parser.parse(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertNotNull(fragments);
+                assertFalse(
+                        fragments.isEmpty(), "a clean ruled grid must be detected in lattice mode");
+                TableFragment f = fragments.get(0);
+                assertFragmentWellFormed(f, 1, 0);
+                assertTrue(f.columnCount() >= 1, "a detected grid must have at least one column");
+                assertFalse(f.rawRows().isEmpty(), "a detected grid must have rows");
+            }
+        }
+
+        @Test
+        @DisplayName("convenience overload with page number routes to lattice mode")
+        void parseByPageNumberDetectsGrid() throws Exception {
+            byte[] pdf = pdfWithGrid();
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments = parser.parse(doc, 1);
+                assertNotNull(fragments);
+                assertFalse(fragments.isEmpty());
+                assertEquals(1, fragments.get(0).pageNumber());
+            }
+        }
+
+        @Test
+        @DisplayName("cell text is normalised (trimmed, newlines collapsed)")
+        void latticeCellTextIsNormalised() throws Exception {
+            byte[] pdf = pdfWithGrid();
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                List<TableFragment> fragments =
+                        parser.parse(doc, new RawPage(1, 0f, 0f, List.of()));
+                assertFalse(fragments.isEmpty());
+                for (List<String> row : fragments.get(0).rawRows()) {
+                    for (String cell : row) {
+                        assertNotNull(cell);
+                        assertFalse(cell.contains("\n"), "newlines must be collapsed");
+                        assertFalse(cell.contains("\r"), "carriage returns must be collapsed");
+                        assertEquals(cell.trim(), cell, "cell text must be trimmed");
+                    }
+                }
+            }
+        }
+    }
+
+    // ── contract invariants ──────────────────────────────────────────────────
+
+    @Nested
+    @DisplayName("Contract invariants")
+    class ContractInvariants {
+
+        @Test
+        @DisplayName("parse never returns null")
+        void parseNeverReturnsNull() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"abc"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                assertNotNull(parser.parse(doc, new RawPage(1, 0f, 0f, List.of())));
+                assertNotNull(parser.parse(doc, 1));
+                assertNotNull(parser.parseStream(doc, new RawPage(1, 0f, 0f, List.of())));
+            }
+        }
+
+        @Test
+        @DisplayName("the document is not closed by the parser")
+        void documentRemainsOpenAfterParse() throws Exception {
+            byte[] pdf = pdfWithText(new String[] {"keep me open"});
+            try (PDDocument doc = Loader.loadPDF(pdf)) {
+                parser.parse(doc, new RawPage(1, 0f, 0f, List.of()));
+                parser.parseStream(doc, new RawPage(1, 0f, 0f, List.of()));
+                // ObjectExtractor.close() would close the underlying COSDocument; the parser must
+                // not.
+                assertFalse(
+                        doc.getDocument().isClosed(),
+                        "parser must not close the caller's document");
+                assertEquals(1, doc.getNumberOfPages());
+            }
+        }
+    }
+
+    // ── helpers ──────────────────────────────────────────────────────────────
+
+    /** Asserts every field of a fragment satisfies the documented contract. */
+    private static void assertFragmentWellFormed(
+            TableFragment f, int expectedPage, int expectedIndex) {
+        assertNotNull(f);
+        assertEquals(expectedPage, f.pageNumber());
+        assertEquals("tbl-p" + expectedPage + "-" + expectedIndex, f.tableId());
+        assertNotNull(f.bounds());
+        assertNotNull(f.headers());
+        assertTrue(f.headers().isEmpty(), "headers are deferred to v2 and must be empty");
+        assertNotNull(f.rows());
+        assertNotNull(f.rawRows());
+        assertNotNull(f.warnings());
+        assertSame(null, f.continuedFromPage(), "continuedFromPage is deferred to v2");
+        assertTrue(f.columnCount() >= 0);
+        assertTrue(f.confidence() >= 0f && f.confidence() <= 1f, "confidence must be within [0,1]");
+        assertEquals(f.rawRows().size(), f.rows().size());
+
+        for (TableRow row : f.rows()) {
+            assertNotNull(row.cells());
+            for (TableCell cell : row.cells()) {
+                assertNotNull(cell.text());
+                assertNotNull(cell.bounds());
+                assertEquals(1, cell.colSpan(), "colSpan is always 1 in v1");
+                assertEquals(1, cell.rowSpan(), "rowSpan is always 1 in v1");
+            }
+        }
+    }
+
+    private static byte[] pdfWithText(String[] lines) throws Exception {
+        try (PDDocument doc = new PDDocument()) {
+            PDPage page = new PDPage(PDRectangle.A4);
+            doc.addPage(page);
+            try (PDPageContentStream cs = new PDPageContentStream(doc, page)) {
+                cs.setFont(new PDType1Font(Standard14Fonts.FontName.HELVETICA), 12);
+                cs.setNonStrokingColor(Color.BLACK);
+                float y = 720f;
+                for (String line : lines) {
+                    cs.beginText();
+                    cs.newLineAtOffset(72f, y);
+                    cs.showText(line);
+                    cs.endText();
+                    y -= 20f;
+                }
+            }
+            return save(doc);
+        }
+    }
+
+    private static byte[] blankPdf() throws Exception {
+        try (PDDocument doc = new PDDocument()) {
+            doc.addPage(new PDPage(PDRectangle.A4));
+            return save(doc);
+        }
+    }
+
+    /**
+     * Builds a small 3-row x 3-column ruled grid with text in each cell. The ruled lines make the
+     * table detectable by lattice mode.
+     */
+    private static byte[] pdfWithGrid() throws Exception {
+        try (PDDocument doc = new PDDocument()) {
+            PDPage page = new PDPage(PDRectangle.A4);
+            doc.addPage(page);
+
+            float left = 100f;
+            float right = 400f;
+            float top = 700f;
+            float bottom = 550f;
+            int cols = 3;
+            int rows = 3;
+            float colStep = (right - left) / cols;
+            float rowStep = (top - bottom) / rows;
+
+            try (PDPageContentStream cs = new PDPageContentStream(doc, page)) {
+                cs.setStrokingColor(Color.BLACK);
+                cs.setLineWidth(1f);
+
+                // vertical lines
+                for (int c = 0; c <= cols; c++) {
+                    float x = left + c * colStep;
+                    cs.moveTo(x, bottom);
+                    cs.lineTo(x, top);
+                }
+                // horizontal lines
+                for (int r = 0; r <= rows; r++) {
+                    float yLine = bottom + r * rowStep;
+                    cs.moveTo(left, yLine);
+                    cs.lineTo(right, yLine);
+                }
+                cs.stroke();
+
+                // cell text
+                cs.setFont(new PDType1Font(Standard14Fonts.FontName.HELVETICA), 10);
+                cs.setNonStrokingColor(Color.BLACK);
+                for (int r = 0; r < rows; r++) {
+                    for (int c = 0; c < cols; c++) {
+                        cs.beginText();
+                        cs.newLineAtOffset(left + c * colStep + 5f, top - (r + 1) * rowStep + 6f);
+                        cs.showText("R" + r + "C" + c);
+                        cs.endText();
+                    }
+                }
+            }
+            return save(doc);
+        }
+    }
+
+    private static byte[] save(PDDocument doc) throws Exception {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        doc.save(baos);
+        return baos.toByteArray();
+    }
+}