For optimal testing of new features and plugins in Lumber Plus, it is advisable to create a separate sandbox environment that would imitate the production environment in terms of hardware, software, and configuration. This can effectively ensure that developers can rigorously test their new features and plugins in a secure environment without adversely affecting the live system. Besides, this setup would allow developers to test their features and plugins using different scenarios and data sets.

Furthermore, in a bid to maintain software quality and prevent regression issues, developers should utilize testing frameworks with the automated testing capabilities available in the sandbox environment. The sandbox environment should also enhance team collaboration between developers, stakeholders and quality assurance personnel. By creating a secure and reliable testing platform for new features and plugins, Lumber Plus can ensure the release of high-quality software to its clients.