What aspects cannot be tested ?
The most important aspect that cannot be tested at the moment is contrast. Subjectively a lens with great contrast but rather mediocre resolution looks more snappy, maybe even sharper than a low-contrast lens with a high resolution. However, living in the digital age we can boost contrast (to some degree) via an imaging application today. Beyond contrast there’s no quantitative way to classify the characteristic of the bokeh (out-of-focus blur), the degree of flare and the performance variations across the focus range.
