The core attributes for function testing are coverage, validity, and affordability. Desired characteristics of a function test (plan) are performability and reuseability. Function testing considers whether individual functions (features, groups, of functions, etc) are performing correctly and function test plans are usually based on covering all of the functions adequately with tests. At such a small scale validity is very important for function tests or they have little value. Function testing can be automated which may reduce costs. Automated function testing can be implemented into development procedures (as unit testing often is) which allows for reduced cost through reuse. The test suite can assert that the operation fo the functions tested is unchanged after changes to the SUT by developers.
The core attributes for risk based test design are credibility, information value, motivation, and power and a desirable characteristic of risk test is affordability. Risk based testing seeks to find potential failure modes fo the SUT, produce them, and gather information about their likelihood and consequences. Good risk based test design should find demonstrable bugs which case noteworthy failures in the SUT including failures that may affect other systems. These tests should help convince stakeholders to make needed changes based on the potential risks identified and demonstrated. Risk based testing can vary in it's application between quicktests which are effective for certain common failure types to more complex and expensive failure mode analysis such as that performed by engineers in safety industries.
Core attributes of specification testing are accountability, coverage, and value. Often specification testing is for purposes of determining compliance with formal specification which may have legal weight. In these cases the details fo testing may be published or even be part of the public record through a standards body or court proceeding. In these cases coverage of the entire formal specification by the test plan is completely required and the information gathered is of considerable importance to the organization running the tests. Other kinds of specification testing, such as competitive product analysis, also provide good value to the testing organization.