test: Add edge case tests for PDF TextLine class

Co-authored-by: Oleksandr Klymenko <alexanderklmn@gmail.com> Signed-off-by: Oleksandr Klymenko <alexanderklmn@gmail.com>

Author: alxkm

document-readers/pdf-reader/src/test/java/org/springframework/ai/reader/pdf/layout/TextLineTest.java

@@ -24,6 +24,7 @@
 import org.junit.jupiter.params.provider.MethodSource;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /*
@@ -131,4 +132,71 @@ void testComputeIndexForCharacter_CloseToPreviousWord_WriteTwoCharacters() {
 assertEquals(" AB" + " ".repeat(22), textLine.getLine());
 }
 
+@Test
+void testZeroLineLength() {
+TextLine textLine = new TextLine(0);
+assertEquals(0, textLine.getLineLength());
+assertEquals("", textLine.getLine());
+
+// Writing to zero-length line should not cause issues
+Character character = new Character('A', 0, false, false, false, false);
+textLine.writeCharacterAtIndex(character);
+assertEquals("", textLine.getLine());
+}
+
+@Test
+void testLineLengthNotDivisibleByCharacterWidth() {
+// Test with line length that doesn't divide evenly by
+// OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT
+TextLine textLine = new TextLine(103);
+int expectedLength = 103 / ForkPDFLayoutTextStripper.OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT;
+assertEquals(expectedLength, textLine.getLineLength());
+assertEquals(" ".repeat(expectedLength), textLine.getLine());
+}
+
+@Test
+void testBoundaryConditionsForLineLength() {
+// Test minimum valid line length
+TextLine textLine1 = new TextLine(1);
+assertEquals(0, textLine1.getLineLength()); // 1/4 = 0 in integer division
+assertEquals("", textLine1.getLine());
+
+// Test line length just under OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT
+TextLine textLine2 = new TextLine(3);
+assertEquals(0, textLine2.getLineLength()); // 3/4 = 0 in integer division
+assertEquals("", textLine2.getLine());
+
+// Test line length exactly at OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT
+TextLine textLine3 = new TextLine(ForkPDFLayoutTextStripper.OUTPUT_SPACE_CHARACTER_WIDTH_IN_PT);
+assertEquals(1, textLine3.getLineLength());
+assertEquals(" ", textLine3.getLine());
+}
+
+@Test
+void testWriteCharacterAtNegativeIndex() {
+TextLine textLine = new TextLine(100);
+Character character = new Character('A', -10, false, false, false, false);
+
+textLine.writeCharacterAtIndex(character);
+// Should handle negative index gracefully without throwing exception
+assertEquals(" ".repeat(25), textLine.getLine());
+}
+
+@Test
+void testWriteNonPrintableCharacters() {
+TextLine textLine = new TextLine(100);
+// Test control characters
+Character tab = new Character('\t', 0, false, false, false, false);
+Character newline = new Character('\n', 4, false, false, false, false);
+Character nullChar = new Character('\0', 8, false, false, false, false);
+
+textLine.writeCharacterAtIndex(tab);
+textLine.writeCharacterAtIndex(newline);
+textLine.writeCharacterAtIndex(nullChar);
+
+// Verify how non-printable characters are handled
+String line = textLine.getLine();
+assertNotNull(line);
+}
+
 }