import assert from 'assert' ; import getDecade from '.' ; describe ( 'getDecade' , ( ) => { it ( 'returns the decade for a the given date' , ( ) => { const result = getDecade ( new Date ( 1971 , 10 , 8 ) ) ; assert ( result === 1970 ) ; } ) ; it ( 'accepts a timestamp' , ( ) => { const result = getDecade ( new Date ( 1969 , 6 , 20 ) . getTime ( ) ) ; assert ( result === 1960 ) ; } ) ; it ( 'returns NaN if the given date is invalid' , ( ) => { const result = getDecade ( new Date ( NaN ) ) ; assert ( isNaN ( result ) ) ; } ) ; it ( 'throws TypeError exception if passed less than 1 argument' , ( ) => { assert . throws ( getDecade . bind ( null ) , TypeError ) ; } ) ; } ) ;