[9.x] Add hasSubject method to Mailables (#41575)

* Add hasSubject method

* Add tests for hasSubject

* Update Mailable.php

Co-authored-by: Taylor Otwell <[email protected]>

Author: MaxGiting

src/Illuminate/Mail/Mailable.php

@@ -777,6 +777,17 @@ public function subject($subject)
         return $this;
     }
 
+    /**
+     * Determine if the mailable has the given subject.
+     *
+     * @param  string  $subject
+     * @return bool
+     */
+    public function hasSubject($subject)
+    {
+        return $this->subject === $subject;
+    }
+
     /**
      * Set the Markdown template for the message.
      *

tests/Mail/MailMailableTest.php

@@ -304,6 +304,13 @@ public function testMailableSetsFromCorrectly()
         }
     }
 
+    public function testMailableSetsSubjectCorrectly()
+    {
+        $mailable = new WelcomeMailableStub;
+        $mailable->subject('foo');
+        $this->assertTrue($mailable->hasSubject('foo'));
+    }
+
     public function testItIgnoresDuplicatedRawAttachments()
     {
         $mailable = new WelcomeMailableStub;