minor #33212 [VarDumper] Add test dump image (ismail1432)

This PR was squashed before being merged into the 4.4 branch (closes #33212).

Discussion
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[VarDumper] Add test dump image

| Q             | A
| ------------- | ---
| Branch?       | 4.4 <!-- see below -->
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   |     <!-- please add some, will be required by reviewers -->
| Fixed tickets | #33107.   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        |  <!-- required for new features -->

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 - Bug fixes must be submitted against the lowest maintained branch where they apply
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 - Features and deprecations must be submitted against branch 4.4.
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Commits
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8393a9b5c1 [VarDumper] Add test dump image

src/Symfony/Component/VarDumper/Tests/Dumper/HtmlDumperTest.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\VarDumper\Tests\Dumper;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\VarDumper\Caster\ImgStub;
 use Symfony\Component\VarDumper\Cloner\VarCloner;
 use Symfony\Component\VarDumper\Dumper\HtmlDumper;
 
@@ -160,4 +161,27 @@ EOTXT
             $out
         );
     }
+
+    /**
+     * @dataProvider varToDumpProvider
+     */
+    public function testDumpString($var, $needle)
+    {
+        $dumper = new HtmlDumper();
+        $cloner = new VarCloner();
+
+        ob_start();
+        $dumper->dump($cloner->cloneVar($var));
+        $out = ob_get_clean();
+
+        $this->assertStringContainsString($needle, $out);
+    }
+
+    public function varToDumpProvider()
+    {
+        return [
+            [['dummy' => new ImgStub('dummy', 'img/png', '100em')], '<img src="data:img/png;base64,ZHVtbXk=" />'],
+            ['foo', '<span class=sf-dump-str title="3 characters">foo</span>'],
+        ];
+    }
 }