tests: add test for PHPMailer encoding bleeding between wp_mail() calls

Author: R1shabh-Gupta

tests/phpunit/tests/pluggable/wpMail.php

@@ -554,4 +554,22 @@ public function test_wp_mail_resets_properties() {
 		$phpmailer = $GLOBALS['phpmailer'];
 		$this->assertNotSame( 'user1', $phpmailer->AltBody );
 	}
+
+	/**
+	 * Test that the encoding of the email does not bleed between long and short emails.
+	 *
+	 * @ticket 33972
+	 */
+	function test_wp_mail_encoding_does_not_bleed() {
+		$content = str_repeat( 'A', 1000 );
+		wp_mail( WP_TESTS_EMAIL, 'Looong line testing', $content );
+
+		$mailer = tests_retrieve_phpmailer_instance();
+		$this->assertEquals( 'quoted-printable', $mailer->Encoding );
+
+		wp_mail( WP_TESTS_EMAIL, 'A follow up short email', 'Short email –' );
+
+		$mailer = tests_retrieve_phpmailer_instance();
+		$this->assertEquals( '8bit', $mailer->Encoding );
+	}
 }