In the context of categorizing tests, what does a power test allow?

A power test is designed to assess the upper limits of a test taker's knowledge or skill in a specific subject area, allowing for a range of difficulty among items. The inclusion of a variety of question difficulties, especially with a focus on more challenging items, means that test takers can demonstrate their mastery of complex concepts. When harder items are included and graded based on the ability to answer them correctly, it allows higher achievers to showcase their capabilities, thus providing a more nuanced understanding of their skills.

In contrast, the other choices do not accurately reflect the nature of a power test. Power tests are deliberately made to challenge test takers beyond just easy questions, and they typically do not aim for uniform difficulty across all items. Also, whether or not partial credit is given is more about the scoring methodology rather than the definition of a power test itself. Therefore, the essence of a power test lies in its design to include a range of item difficulty that can help differentiate among test-taker abilities.