Add unit tests

tests/PhpSpreadsheetTests/Reader/Xlsx/Issue4800Test.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PHPUnit\Framework\TestCase;
+
+class Issue4800Test extends TestCase
+{
+    private static string $filename = 'tests/data/Reader/XLSX/issue.4800.xlsx';
+
+    public function testHeaderFooterImageDimensions(): void
+    {
+        $reader = new XlsxReader();
+        $spreadsheet = $reader->load(self::$filename);
+
+        foreach ($spreadsheet->getAllSheets() as $sheet) {
+            $images = $sheet->getHeaderFooter()->getImages();
+            self::assertCount(1, $images);
+
+            $image = reset($images);
+            self::assertSame(100, $image->getWidth());
+            self::assertSame(100, $image->getHeight());
+        }
+
+        $spreadsheet->disconnectWorksheets();
+    }
+}