Refactored the implementation in Calendar#date_yesterday by assigning (1 * 60 * 60 * 24) to a constant SECONDS_IN_ONE_DAY and using this constant in the method.

Refactored the spec

 context "#date_yesterday"
     it "returns yesterday's date"

by replacing  (1 * 60 * 60 * 24) with Calendar::SECONDS_IN_ONE_DAY