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Short tests reward a fast start. A five-minute test shows how fast you type when you have to keep going, which is what employers, exams and real work measure. Expect your result to be a few WPM lower than in a one-minute test: that is normal and it is the more honest number.
Relax your shoulders and wrists, breathe normally and keep a steady rhythm instead of bursts. After the test, look at the consistency figure and the speed chart: a flat line is better than peaks and drops. If accuracy falls in the last minute, take short breaks during practice and build up gradually from the 1-minute test.