ACTFL assessments are designed specifically to measure language proficiency, how well a person creates, functions and applies language in real life situations.
Most language tests are designed to measure discrete functions like grammar, how well a person can perform on a specific test, or on information specific to a certain curriculum, and not how well they can actually use the language.
Although many tests bill themselves as “proficiency” tests, only ACTFL tests are designed to assess proficiency in its purest form, without artificial constructs that don’t replicate true-life speaking encounters.