Refactor RemoveAnimationModifier::class, Add tests

src/Drivers/Gd/Modifiers/RemoveAnimationModifier.php

@@ -18,7 +18,7 @@ class RemoveAnimationModifier extends GenericRemoveAnimationModifier implements
     public function apply(ImageInterface $image): ImageInterface
     {
         $image->core()->setNative(
-            $this->chosenFrame($image, $this->position)->native()
+            $this->selectedFrame($image)->native()
         );
 
         return $image;

src/Drivers/Imagick/Modifiers/RemoveAnimationModifier.php

@@ -15,7 +15,7 @@ class RemoveAnimationModifier extends GenericRemoveAnimationModifier implements
     {
         // create new imagick with just one image
         $imagick = new Imagick();
-        $frame = $this->chosenFrame($image, $this->position);
+        $frame = $this->selectedFrame($image);
         $imagick->addImage($frame->native()->getImage());
 
         // set new imagick to image

src/Modifiers/RemoveAnimationModifier.php

@@ -19,13 +19,30 @@ class RemoveAnimationModifier extends SpecializableModifier
     /**
      * @throws RuntimeException
      */
-    public function chosenFrame(ImageInterface $image, int|string $position): FrameInterface
+    protected function selectedFrame(ImageInterface $image): FrameInterface
     {
-        if (is_int($position)) {
-            return $image->core()->frame($position);
+        return $image->core()->frame($this->normalizePosition($image));
+    }
+
+    /**
+     * Return the position of the selected frame as integer
+     *
+     * @param ImageInterface $image
+     * @throws InputException
+     * @return int
+     */
+    protected function normalizePosition(ImageInterface $image): int
+    {
+        if (is_int($this->position)) {
+            return $this->position;
         }
 
-        if (preg_match("/^(?P<percent>[0-9]{1,3})%$/", $position, $matches) != 1) {
+        if (is_numeric($this->position)) {
+            return (int) $this->position;
+        }
+
+        // calculate position from percentage value
+        if (preg_match("/^(?P<percent>[0-9]{1,3})%$/", $this->position, $matches) != 1) {
             throw new InputException(
                 'Position must be either integer or a percent value as string.'
             );
@@ -35,6 +52,6 @@ class RemoveAnimationModifier extends SpecializableModifier
         $position = intval(round($total / 100 * intval($matches['percent'])));
         $position = $position == $total ? $position - 1 : $position;
 
-        return $image->core()->frame($position);
+        return $position;
     }
 }

tests/Unit/Modifiers/RemoveAnimationModifierTest.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Image\Tests\Unit\Modifiers;
+
+use Generator;
+use Intervention\Image\Interfaces\ImageInterface;
+use Intervention\Image\Modifiers\RemoveAnimationModifier;
+use Intervention\Image\Tests\BaseTestCase;
+use Mockery;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+
+#[CoversClass(RemoveAnimationModifier::class)]
+final class RemoveAnimationModifierTest extends BaseTestCase
+{
+    #[DataProvider('normalizePositionProvider')]
+    public function testNormalizePosition(int|string $position, int $frames, int $normalized): void
+    {
+        $modifier = new class ($position) extends RemoveAnimationModifier
+        {
+            public function testResult(int $frames): int
+            {
+                $image = Mockery::mock(ImageInterface::class)->makePartial();
+                $image->shouldReceive('count')->andReturn($frames);
+
+                return $this->normalizePosition($image);
+            }
+        };
+
+        $this->assertEquals($normalized, $modifier->testResult($frames));
+    }
+
+    public static function normalizePositionProvider(): Generator
+    {
+        yield [0, 100, 0];
+        yield [10, 100, 10];
+        yield ['10', 100, 10];
+        yield ['0%', 100, 0];
+        yield ['50%', 100, 50];
+        yield ['100%', 100, 99];
+    }
+}