Add unit tests for ChartSheet reading

tests/PhpSpreadsheetTests/Reader/Xlsx/ChartSheetTest.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
+use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
+use PHPUnit\Framework\TestCase;
+
+class ChartSheetTest extends TestCase
+{
+    public function testLoadChartSheetWithCharts(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/ChartSheet.xlsx';
+        $reader = new Xlsx();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($filename);
+
+        self::assertCount(2, $spreadsheet->getAllSheets());
+        $chartSheet = $spreadsheet->getSheetByName('Chart1');
+        self::assertInstanceOf(Worksheet::class, $chartSheet);
+        self::assertSame(1, $chartSheet->getChartCount());
+    }
+
+    public function testLoadChartSheetWithoutCharts(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/ChartSheet.xlsx';
+        $reader = new Xlsx();
+        $reader->setIncludeCharts(false);
+        $spreadsheet = $reader->load($filename);
+
+        self::assertCount(1, $spreadsheet->getAllSheets());
+        $chartSheet = $spreadsheet->getSheetByName('Chart1');
+        self::assertNull($chartSheet);
+    }
+}