Learn French: Pendant l'essai, il conduit le moins habilement. - During the test, he drives the least skillfully.

Because habilement is an adverb (skillfully), and adverbs do not have gender. When you make a superlative with an adverb, you always use the invariable le plus or le moins. You only change the article to la or les when making a superlative with an adjective that describes a noun.

How is the adverb habilement formed?

It is formed from the adjective habile (skillful or clever). The rule for making adverbs in French is to add -ment to the feminine form of the adjective. Since habile already ends in an -e in its masculine form, it is the same in the feminine, so we just add -ment directly.

What are the different meanings of un essai?

Un essai can mean a test or trial, as in this sentence where it likely refers to a test drive. It can also mean an attempt or a written essay.

Could I use pour instead of pendant to say during the test?

No, pendant is specifically used to express 'during' a period or event. If you said pour l'essai, it would mean he is driving 'for the test' (in order to pass it or prepare for it), rather than saying the driving happened 'during' that time.