diff --git a/tests/Functional/Value/SizeTest.php b/tests/Functional/Value/SizeTest.php
new file mode 100644
index 00000000..b9ca0a97
--- /dev/null
+++ b/tests/Functional/Value/SizeTest.php
@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Functional\Value;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\OutputFormat;
+use Sabberworm\CSS\Value\Size;
+
+/**
+ * @covers \Sabberworm\CSS\Value\Size
+ */
+final class SizeTest extends TestCase
+{
+    /**
+     * @return array<non-empty-string, array{0: float, 1: non-empty-string}>
+     */
+    public static function provideNumberMaybeNearZeroAndExpectedRendering(): array
+    {
+        return [
+            '1e-7' => [1e-7, '.0000001'],
+            '-1e-7' => [-1e-7, '-.0000001'],
+            '1.23456789e-5' => [1.23456789e-5, '.0000123456789'],
+            '-2.5e-8' => [-2.5e-8, '-.000000025'],
+            '1e-5' => [1e-5, '.00001'],
+        ];
+    }
+
+    /**
+     * @test
+     *
+     * @dataProvider provideNumberMaybeNearZeroAndExpectedRendering
+     */
+    public function renderWritesNumberInValidCssSyntaxWithoutLosingDigits(float $number, string $expected): void
+    {
+        $subject = new Size($number, 'px');
+
+        self::assertSame($expected . 'px', $subject->render(OutputFormat::create()));
+    }
+}
diff --git a/tests/Unit/Value/SizeTest.php b/tests/Unit/Value/SizeTest.php
index 2352bd56..afa4b565 100644
--- a/tests/Unit/Value/SizeTest.php
+++ b/tests/Unit/Value/SizeTest.php
@@ -5,7 +5,6 @@
 namespace Sabberworm\CSS\Tests\Unit\Value;
 
 use PHPUnit\Framework\TestCase;
-use Sabberworm\CSS\OutputFormat;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Settings;
 use Sabberworm\CSS\Value\PrimitiveValue;
@@ -199,32 +198,6 @@ public function getArrayRepresentationIncludesUnit(): void
         self::assertSame('px', $result['unit']);
     }
 
-    /**
-     * @return array<non-empty-string, array{0: float, 1: non-empty-string}>
-     */
-    public static function provideNumberNearZeroAndExpectedRendering(): array
-    {
-        return [
-            '1e-7' => [1e-7, '.0000001px'],
-            '-1e-7' => [-1e-7, '-.0000001px'],
-            '1.23456789e-5' => [1.23456789e-5, '.0000123456789px'],
-            '-2.5e-8' => [-2.5e-8, '-.000000025px'],
-            '1e-5' => [1e-5, '.00001px'],
-        ];
-    }
-
-    /**
-     * @test
-     *
-     * @dataProvider provideNumberNearZeroAndExpectedRendering
-     */
-    public function renderWritesNumberNearZeroWithoutLosingDigits(float $number, string $expected): void
-    {
-        $subject = new Size($number, 'px');
-
-        self::assertSame($expected, $subject->render(OutputFormat::create()));
-    }
-
     /**
      * @param array<non-empty-string> $units
      *