The objective of accelerated testing is estimating when failure would occur under the conditions of the engineering application. For such accelerated tests to provide useful information, the mode of failure needs to be the same as then expected in the application. Further, the accelerated testing needs to provide information in a statistical framework that can be used to estimate the statistical performance of the application. Again, the Abernethy reference  provides a useful guide for conducting experiments in a statistical framework.
In addition to testing to determine dependencies of modes upon principal variables, testing to understand the behavior of integrated systems is often useful. In the steam power industry "model boiler" testing is often carried out; such testing assesses how elements of the system interact. Such integrated engineering tests are widely used and provide valuable information for guiding system design.
Lifetime Prediction, Roger W. Staehle, Adjunct Professor, Department of Chemical Engineering and Materials Science, University of Minnesota, Staehle Consulting Co.