Add PHPUnit test cases for merge behavior

Author: mpdude

extra/html-extra/Tests/HtmlAttrMergeTest.php

@@ -12,14 +12,17 @@
 namespace Twig\Extra\Html\Tests;
 
 use PHPUnit\Framework\TestCase;
+use Twig\Error\RuntimeError;
+use Twig\Extra\Html\HtmlAttr\AttributeValueInterface;
+use Twig\Extra\Html\HtmlAttr\MergeableInterface;
 use Twig\Extra\Html\HtmlExtension;
 
 class HtmlAttrMergeTest extends TestCase
 {
     /**
      * @dataProvider htmlAttrProvider
      */
-    public function testMerge(array $expected, array $inputs)
+    public function testMerge(array $expected, array $inputs): void
     {
         $result = HtmlExtension::htmlAttrMerge(...$inputs);
 
@@ -126,5 +129,94 @@ public static function htmlAttrProvider(): \Generator
                 ['style' => ['color' => 'red']],
             ],
         ];
+
+        // MergeableInterface
+        yield 'MergeableInterface mergeInto is called when new value implements interface' => [
+            ['class' => 'merged: old + new'],
+            [
+                ['class' => 'old'],
+                ['class' => new MergeableStub('new')],
+            ],
+        ];
+
+        yield 'MergeableInterface appendFrom is called when existing value implements interface' => [
+            ['class' => 'appended: old + new'],
+            [
+                ['class' => new MergeableStub('old')],
+                ['class' => 'new'],
+            ],
+        ];
+
+        yield 'MergeableInterface mergeInto is called when both implement interface' => [
+            ['class' => 'merged: value1 + value2'],
+            [
+                ['class' => new MergeableStub('value1')],
+                ['class' => new MergeableStub('value2')],
+            ],
+        ];
+
+        yield 'MergeableInterface with array value' => [
+            ['class' => 'appended: base + extra1, extra2'],
+            [
+                ['class' => new MergeableStub('base')],
+                ['class' => ['extra1', 'extra2']],
+            ],
+        ];
+
+        // Scalar and object merging
+        yield 'string replaces object' => [
+            ['value' => 'new-string'],
+            [
+                ['value' => new \stdClass()],
+                ['value' => 'new-string'],
+            ],
+        ];
+
+        yield 'object replaces string' => [
+            ['value' => new \stdClass()],
+            [
+                ['value' => 'old-string'],
+                ['value' => new \stdClass()],
+            ],
+        ];
+    }
+
+    public function testIncompatibleValuesMergeThrowsException(): void
+    {
+        $this->expectException(RuntimeError::class);
+        $this->expectExceptionMessage('Cannot merge incompatible values for key "test"');
+
+        HtmlExtension::htmlAttrMerge(
+            ['test' => ['array']],
+            ['test' => 'scalar']
+        );
+    }
+}
+
+class MergeableStub implements MergeableInterface
+{
+    public function __construct(private readonly mixed $value)
+    {
+    }
+
+    public function mergeInto(mixed $previous): self
+    {
+        $previousValue = $previous instanceof self ? $previous->value : $previous;
+        return new self("merged: {$previousValue} + {$this->value}");
+    }
+
+    public function appendFrom(mixed $newValue): self
+    {
+        if (is_array($newValue)) {
+            $newValue = implode(', ', $newValue);
+        } elseif ($newValue instanceof self) {
+            $newValue = $newValue->value;
+        }
+        return new self("appended: {$this->value} + {$newValue}");
+    }
+
+    public function __toString(): string
+    {
+        return (string) $this->value;
     }
 }

extra/html-extra/Tests/HtmlAttrTest.php

@@ -22,7 +22,7 @@ class HtmlAttrTest extends TestCase
     /**
      * @dataProvider htmlAttrProvider
      */
-    public function testPrintingAttributes(string $expected, array $inputs)
+    public function testPrintingAttributes(string $expected, array $inputs): void
     {
         $result = HtmlExtension::htmlAttr(new Environment(new ArrayLoader()), ...$inputs);
 
@@ -228,6 +228,35 @@ public static function htmlAttrProvider(): \Generator
                 ['data-count' => 0],
             ],
         ];
+
+        // Scalar and object merging in rendering
+        yield 'string replaces object in rendering' => [
+            'value="new-string"',
+            [
+                ['value' => new \stdClass()],
+                ['value' => 'new-string'],
+            ],
+        ];
+
+        yield 'object replaces string in rendering uses __toString if available' => [
+            'value="stringable-object"',
+            [
+                ['value' => 'old-string'],
+                ['value' => new StringableStub('stringable-object')],
+            ],
+        ];
+    }
+}
+
+class StringableStub implements \Stringable
+{
+    public function __construct(private readonly string $value)
+    {
+    }
+
+    public function __toString(): string
+    {
+        return $this->value;
     }
 }