[feature] add TestEmail::assertSubjectContains()

README.md

@@ -44,6 +44,7 @@ class MyTest extends KernelTestCase // or WebTestCase
         $this->mailer()->assertEmailSentTo('kevin@example.com', function(TestEmail $email) {
             $email
                 ->assertSubject('Email Subject')
+                ->assertSubjectContains('Subject')
                 ->assertFrom('from@example.com')
                 ->assertReplyTo('reply@example.com')
                 ->assertCc('cc1@example.com')

src/TestEmail.php

@@ -122,6 +122,13 @@ final public function assertSubject(string $expected): self
         return $this;
     }
 
+    final public function assertSubjectContains(string $needle): self
+    {
+        Assert::that($this->email->getSubject())->contains($needle);
+
+        return $this;
+    }
+
     final public function assertFrom(string $expectedEmail, string $expectedName = ''): self
     {
         foreach ($this->email->getFrom() as $address) {

tests/InteractsWithMailerTest.php

@@ -63,6 +63,7 @@ public function can_assert_email_sent(string $environment): void
                     ->assertCc('cc@example.com')
                     ->assertBcc('bcc@example.com')
                     ->assertReplyTo('reply@example.com')
+                    ->assertSubjectContains('sub')
                     ->assertHtmlContains('html body')
                     ->assertTextContains('text body')
                     ->assertContains('body')