Usually increasing of the team of testers requires in cases when the company is rapidly expanding its business and has no time to recruit enough staff or when company faced with a temporary surge of activity in the market, but does not want to inflate the staff or if software testing is urgently needed for a few releases of the software simultaneously.
All this is a good opportunity to access outsourcing of software testing; testing agencies are aware of this and, as a rule, are ready to offer the necessary amount of resources quickly. Of course, you should be ready for the fact that the cost of solving the problems quickly will be a little above than average.
The main problem of this approach is management of resources. You should not rely on self-organization of attracted testers. A good test agency will certainly help to solve most of problems, but the cargo of a general management remains to the project manager (see picture). What are the qualities required of a test leader? First of all, the ability to accurately determine the need for additional resources, quickly find solutions to identified problems and to maintain good relations with the involvement of staff.
Most of the problems associated with communication, information exchange and an established production process in a company, can be decided if you create a partner relationship with the test agency in advance. Even if at the moment work is going in the normal rhythm in your organization, but if you predict a sharp burst of activity in the nearest future, it is advisable to pre-plan for it. It's no secret that for anyone, even highly qualified specialist, it takes time for entry into a new project; review the order of development, testing tools and other features of your organization. It is advisable to go through this stage in advance, coordinating all the formalities so that with the appearance of need for testers they could get to work with minimal delay.
This approach would help to solve another important task. For a quick and effective start of work you need people with high qualifications in the subject area of your project. With high probability, such specialists will not be available, but if you have an agreement of the possibility of working together in advance, then the test agency may have time to train and upgrade the skills of their staff. In any case, when you provide the tester, you should be familiar with his resume and see if he has any skills in your subject area.