import assert from 'assert' ; import differenceInYears from '.' ; describe ( 'differenceInYears' , ( ) => { it ( 'returns the number of full years between the given dates' , ( ) => { const result = differenceInYears ( new Date ( 2012 , 6 , 2 , 18 , 0 ) , new Date ( 2011 , 6 , 2 , 6 , 0 ) ) ; assert ( result === 1 ) ; } ) ; it ( 'returns a negative number if the time value of the first date is smaller' , ( ) => { const result = differenceInYears ( new Date ( 2011 , 6 , 2 , 6 , 0 ) , new Date ( 2012 , 6 , 2 , 18 , 0 ) ) ; assert ( result === - 1 ) ; } ) ; it ( 'accepts timestamps' , ( ) => { const result = differenceInYears ( new Date ( 2014 , 6 , 2 ) . getTime ( ) , new Date ( 2010 , 6 , 2 ) . getTime ( ) ) ; assert ( result === 4 ) ; } ) ; describe ( 'leap days' , ( ) => { it ( 'supports past dates with right side after leap day' , ( ) => { const result = differenceInYears ( new Date ( 2004 , 1 , 29 , 0 , 0 ) , new Date ( 2002 , 2 , 1 , 0 , 0 ) ) ; assert ( result === 1 ) ; } ) ; it ( 'supports past dates with right side before leap day' , ( ) => { const result = differenceInYears ( new Date ( 2004 , 1 , 29 , 0 , 0 ) , new Date ( 2002 , 1 , 28 , 0 , 0 ) ) ; assert ( result === 2 ) ; } ) ; it ( 'supports future dates' , ( ) => { const result = differenceInYears ( new Date ( 2004 , 1 , 29 , 0 , 0 ) , new Date ( 2006 , 2 , 1 , 0 , 0 ) ) ; assert ( result === - 2 ) ; } ) ; it ( 'supports equal dates of same year' , ( ) => { const result = differenceInYears ( new Date ( 2004 , 1 , 29 , 0 , 0 ) , new Date ( 2004 , 1 , 29 , 0 , 0 ) ) ; assert ( result === 0 ) ; } ) ; it ( 'supports equal dates of different years' , ( ) => { const result = differenceInYears ( new Date ( 2008 , 1 , 29 , 0 , 0 ) , new Date ( 2004 , 1 , 29 , 0 , 0 ) ) ; assert ( result === 4 ) ; } ) ; } ) ; describe ( 'edge cases' , ( ) => { it ( 'the difference is less than a year, but the given dates are in different calendar years' , ( ) => { const result = differenceInYears ( new Date ( 2015 , 0 , 1 ) , new Date ( 2014 , 11 , 31 ) ) ; assert ( result === 0 ) ; } ) ; it ( 'the same for the swapped dates' , ( ) => { const result = differenceInYears ( new Date ( 2014 , 11 , 31 ) , new Date ( 2015 , 0 , 1 ) ) ; assert ( result === 0 ) ; } ) ; it ( 'the days and months of the given dates are the same' , ( ) => { const result = differenceInYears ( new Date ( 2014 , 8 , 5 ) , new Date ( 2012 , 8 , 5 ) ) ; assert ( result === 2 ) ; } ) ; it ( 'the given dates are the same' , ( ) => { const result = differenceInYears ( new Date ( 2014 , 8 , 5 , 0 , 0 ) , new Date ( 2014 , 8 , 5 , 0 , 0 ) ) ; assert ( result === 0 ) ; } ) ; it ( 'does not return -0 when the given dates are the same' , ( ) => { function isNegativeZero ( x ) { return x === 0 && 1 / x < 0 ; } const result = differenceInYears ( new Date ( 2014 , 8 , 5 , 0 , 0 ) , new Date ( 2014 , 8 , 5 , 0 , 0 ) ) ; const resultIsNegative = isNegativeZero ( result ) ; assert ( resultIsNegative === false ) ; } ) ; } ) ; it ( 'returns NaN if the first date is `Invalid Date`' , ( ) => { const result = differenceInYears ( new Date ( NaN ) , new Date ( 2017 , 0 , 1 ) ) ; assert ( isNaN ( result ) ) ; } ) ; it ( 'returns NaN if the second date is `Invalid Date`' , ( ) => { const result = differenceInYears ( new Date ( 2017 , 0 , 1 ) , new Date ( NaN ) ) ; assert ( isNaN ( result ) ) ; } ) ; it ( 'returns NaN if the both dates are `Invalid Date`' , ( ) => { const result = differenceInYears ( new Date ( NaN ) , new Date ( NaN ) ) ; assert ( isNaN ( result ) ) ; } ) ; it ( 'throws TypeError exception if passed less than 2 arguments' , ( ) => { assert . throws ( differenceInYears . bind ( null ) , TypeError ) ; assert . throws ( differenceInYears . bind ( null , 1 ) , TypeError ) ; } ) ; } ) ;