diff --git tests/phpunit/testcases/messages/functions.php tests/phpunit/testcases/messages/functions.php
index 949d129..139371f 100644
--- tests/phpunit/testcases/messages/functions.php
+++ tests/phpunit/testcases/messages/functions.php
@@ -41,4 +41,21 @@ class BP_Tests_Messages_Functions extends BP_UnitTestCase {
 		$this->assertEquals( 1, messages_get_unread_count( $u2 ) );
 	}
 
+	/**
+	 * @group messages_new_message
+	 */
+	public function test_messages_new_message_invalid_recipient_error_message() {
+		$u1 = $this->factory->user->create();
+
+		// attempt to send a private message to an invalid username
+		$t1 = messages_new_message( array(
+			'sender_id'  => $u1,
+			'recipients' => array( 'homerglumpkin' ),
+			'subject'    => 'A new message',
+			'content'    => 'Hey there!',
+			'error_type' => 'wp_error'
+		) );
+
+		$this->assertSame( 'Message could not be sent because you have entered an invalid username. Please try again.', $t1->get_error_message() );
+	}
 }