5 random tests are too small. Consider increasing them to at least 100 to ensure faulty solutions don't pass.

Missing edge case tests with speed == 0 && desiredLength == 0: https://www.codewars.com/kata/reviews/57b99f05a09e1c192d00008e/groups/5e2b1e715c9ce60001a18e7c

Some solution pass all fixed tests and sometimes pass all random tests: https://www.codewars.com/kata/reviews/57b99f05a09e1c192d00008e/groups/5e2b1af7a778610001f7ddc3

Test.assertSimilar(beardGrower(1, 1, 5), ['1 shave', '4 days'], 'should work for basic cases')
Why not ['No shave', '5 days']? ;-)

Test.assertSimilar(beardGrower(1, 1, 50), ['4 shaves', '14 days'], 'and for larger beards')
Why not ['4 shave', '10 days']? ;-)