Add tests for some of the date modifiers

tests/Modifiers/FormatTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use Illuminate\Support\Carbon;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class FormatTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        config()->set('statamic.system.display_timezone', 'Europe/Berlin'); // +1 hour
+    }
+
+    #[Test]
+    public function it_formats_date()
+    {
+        $this->assertSame('1st January 2025 3:45pm', $this->modify(Carbon::parse('2025-01-01 15:45'), 'jS F Y g:ia'));
+    }
+
+    public function modify($value, $format)
+    {
+        return Modify::value($value)->format($format)->fetch();
+    }
+}

tests/Modifiers/FormatTranslatedTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use Illuminate\Support\Carbon;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class FormatTranslatedTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        Carbon::setLocale('de');
+
+        config()->set('statamic.system.display_timezone', 'Europe/Berlin'); // +1 hour
+    }
+
+    #[Test]
+    public function it_formats_date()
+    {
+        $this->assertSame('Mittwoch 1 Januar 2025, 15:45', $this->modify(Carbon::parse('2025-01-01 15:45'), 'l j F Y, H:i'));
+    }
+
+    public function modify($value, $format)
+    {
+        return Modify::value($value)->formatTranslated($format)->fetch();
+    }
+}

tests/Modifiers/IsoFormatTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use Illuminate\Support\Carbon;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class IsoFormatTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        config()->set('statamic.system.display_timezone', 'Europe/Berlin'); // +1 hour
+    }
+
+    #[Test]
+    public function it_formats_date()
+    {
+        $this->assertSame('2025.01.01 15:45', $this->modify(Carbon::parse('2025-01-01 15:45'), 'YYYY.MM.DD HH:mm'));
+    }
+
+    public function modify($value, $format)
+    {
+        return Modify::value($value)->isoFormat($format)->fetch();
+    }
+}

tests/Modifiers/ModifyDateTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use Illuminate\Support\Carbon;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class ModifyDateTest extends TestCase
+{
+    #[Test]
+    public function it_modifies_date()
+    {
+        $this->assertEquals($this->modify(Carbon::parse('2025-01-01'), '+2 months')->format('Y-m-d'), '2025-03-01');
+    }
+
+    public function modify($value, $modify)
+    {
+        return Modify::value($value)->modifyDate($modify)->fetch();
+    }
+}

tests/Modifiers/TimezoneTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use Illuminate\Support\Carbon;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class TimezoneTest extends TestCase
+{
+    #[Test]
+    public function it_converts_date_into_timezone()
+    {
+        $this->assertEquals(
+            $this->modify(Carbon::parse('2025-01-01 15:45'), 'Europe/Berlin')->format('Y-m-d H:i'),
+            '2025-01-01 16:45'
+        );
+    }
+
+    public function modify($value, $timezone)
+    {
+        return Modify::value($value)->timezone($timezone)->fetch();
+    }
+}