Tests were failing because of table naming… sorry for that.

lib/php-activerecord/test/sql/mysql.sql

···
     id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
 ) ENGINE=InnoDB;
 
-CREATE TABLE usernewsletters (
+CREATE TABLE user_newsletters (
     id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
     user_id INT NOT NULL,
     newsletter_id INT NOT NULL

lib/php-activerecord/test/sql/sqlite.sql

···
     id INTEGER NOT NULL PRIMARY KEY
 );
 
-CREATE TABLE usernewsletters (
+CREATE TABLE user_newsletters (
     id INTEGER NOT NULL PRIMARY KEY,
     user_id INTEGER NOT NULL,
     newsletter_id INTEGER NOT NULL