Candidates who get higher IELTS scores tend to use a wider range of vocabulary. A quick way to test your 'vocabulary range' is to challenge yourself to explain something in as many different ways as possible.
Example: I asked my students to explain the word 'recreation'
doing things that you enjoy
Longer answer showing a wider vocabulary range:
doing things that you enjoy; activities for fun or pleasure; leisure activities; what you do in your free time outside work; maybe pastimes or hobbies; it could include sports, games, or just relaxing and unwinding when you have time to yourself...