During test analysis and design the test approach for non-functional testing is translated into tangible test conditions and test cases.
This should be part of the overall approach to test specification and design and should include full traceability back to the requirements and risk assessment.
Although there are specific elements to non-functional test specification, the design and preparation should follow the same, established, processes.
SP 3.1 Identify and prioritise non-functional test conditions
SP 3.2 Identify and prioritise non-functional test cases
SP 3.3 Identify necessary specific test data
SP 3.4 Maintain horizontal traceability with non-functional requirements
As with all types of testing, a list of requirements should be produced. In this case they are non-functional requirements.
The requirements must drive test design along with the risk analysis, in order to design tests which are prioritised and appropriate.
It is a common problem for non-functional requirements to be poorly conceived.