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Get enough sleep to overcome test anxiety:  Get at least eight-10 hours of sleep the night before the test as big tests require a lot of energy and stamina to be able to focus for several hours.
Relax and Have fun: To get your mind and emotions more relaxed in the time leading up to [...]

Tips to manage test anxiety -Take a look at your diet
What to eat to improve memory and concentration

Consume more complex carbohydrates, such as fruits (including oranges, pears,tangerines, grapefruit, apples, and kiwi) and some vegetables.
 high-protein diet, including, cheese, beans,eggs, meat, and nuts. Add protein foods in the morning and snacks for better concentration. [...]

Test anxiety in children has been the subject of empirical investigation for the past 30 years  and its correlation with poor academic performance has been established.
Test anxiety in children test anxiety has been associated with depressed academic performance  The debilitating effects of test anxiety on performance in school and on intelligence tests, achievement tests, [...]