improve test coverage
improve test coverage

ThisIsPuzzle/Aura.Sql,auraphp/Aura.SqlSchema,gsouf/Aura.SqlQuery,harikt/Aura.SqlQuery,sasha-ch/Aura.Sql,auraphp/Aura.SqlQuery,paska27/sql-builder,frederikbosch/Aura.Sql,jakejohns/Aura.SqlSchema,cxj/Aura.SqlMapper_Bundle,dstockto/Aura.SqlQuery,cxj/Aura.SqlQuery,auraphp/Aura.SqlMapper_Bundle,JLacoude/Aura.Sql,NateJacobs/Aura.Sql,auraphp/Aura.Sql