faster spreadsheet exporter based on opensout and other export improvements (#5238)

tests/Export/Package/CellFormatter/DateFormatterTest.php

@@ -0,0 +1,43 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Tests\Export\Package\CellFormatter;
+
+use App\Export\Package\CellFormatter\DateFormatter;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \App\Export\Package\CellFormatter\DateFormatter
+ */
+class DateFormatterTest extends TestCase
+{
+    public function testFormatValueReturnsFormattedDateForDateTime(): void
+    {
+        $formatter = new DateFormatter();
+        $date = new \DateTime('2023-10-01');
+        $result = $formatter->formatValue($date);
+        self::assertEquals('2023-10-01', $result);
+    }
+
+    public function testFormatValueReturnsNullForNullValue(): void
+    {
+        $formatter = new DateFormatter();
+        $result = $formatter->formatValue(null);
+        self::assertNull($result);
+    }
+
+    public function testFormatValueThrowsExceptionForNonDateTime(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Only DateTimeInterface can be formatted');
+
+        $formatter = new DateFormatter();
+        $formatter->formatValue('not a date');
+    }
+}