Add tests for HtmlString (#51666)

tests/Support/SupportHtmlStringTest.php

@@ -7,11 +7,31 @@
 
 class SupportHtmlStringTest extends TestCase
 {
-    public function testToHtml()
+    public function testToHtml(): void
     {
+        // Check if HtmlString correctly converts a basic HTML string
         $str = '<h1>foo</h1>';
         $html = new HtmlString('<h1>foo</h1>');
         $this->assertEquals($str, $html->toHtml());
+
+        // Check if HtmlString correctly preserves leading blank spaces in the HTML string
+        $startWithBlankSpaces = '   <h1>      foo</h1>';
+        $html = new HtmlString('   <h1>      foo</h1>');
+        $this->assertEquals($startWithBlankSpaces, $html->toHtml());
+
+        // Check if HtmlString correctly preserves trailing blank spaces in the HTML string
+        $endsWithBlankSpaces = '<h1>foo       </h1>   ';
+        $html = new HtmlString('<h1>foo       </h1>   ');
+        $this->assertEquals($endsWithBlankSpaces, $html->toHtml());
+
+        // Check if HtmlString correctly handles an empty string
+        $emptyHtml = new HtmlString('');
+        $this->assertEquals('', $emptyHtml->toHtml());
+
+        // Check if HtmlString correctly converts a plain text string
+        $str = 'foo bar';
+        $html = new HtmlString($str);
+        $this->assertEquals($str, $html->toHtml());
     }
 
     public function testToString()
@@ -21,9 +41,16 @@ public function testToString()
         $this->assertEquals($str, (string) $html);
     }
 
-    public function testIsEmpty()
+    public function testIsEmpty(): void
     {
+        // Check if HtmlString correctly identifies an empty string as empty
         $this->assertTrue((new HtmlString(''))->isEmpty());
+
+        // HtmlString with whitespace should not be considered as empty
+        $this->assertFalse((new HtmlString('   '))->isEmpty());
+
+        // HtmlString with content should not be considered as empty
+        $this->assertFalse((new HtmlString('<p>Hello</p>'))->isEmpty());
     }
 
     public function testIsNotEmpty()