The Big Five Inventory is the most used measuring tool because it has criterion that expands across different factors in personality, allowing psychologists to have the most accurate information they can garner.
Personality is often broken into statistically-identified factors called the Big Five, which are openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism (or emotional stability).
Trait-based personality theories, such as those defined by Raymond Cattell define personality as the traits that predict a person's behavior.
On the other hand, more behaviorally based approaches define personality through learning and habits.
Ego depletion, or cognitive fatigue, is the use of one's energy to overtly act in a way that is contrary to one's inner disposition.
When people act in a contrary fashion, they divert most, if not all, (cognitive) energy toward regulating this foreign style of behavior and attitudes.
All of these tests are beneficial because they have both reliability and validity, two factors that make a test accurate.
"Each item should be influenced to a degree by the underlying trait construct, giving rise to a pattern of positive intercorrelations so long as all items are oriented (worded) in the same direction." A recent, but not well-known, measuring tool that psychologists use is the 16 PF.
In other words, the study focused on the benefits and drawbacks of introverts (people who are shy, socially inhibited and non-aggressive) acting extraverted, and of extraverts acting introverted.
After acting extraverted, introverts' experience of positive affect increased whereas extraverts seemed to experience lower levels of positive affect and suffered from the phenomenon of ego depletion.