import * as fc from 'fast-check' ; describe ( 'Identity laws for string' , ( ) => { it ( 'any Unicode string should contain itself' , ( ) => { fc . assert ( fc . property ( fc . fullUnicodeString ( ) , ( str ) => str . includes ( str ) ) ) ; } ) ; it ( 'should fail with counterexample' , ( ) => { fc . assert ( fc . property ( fc . fullUnicodeString ( ) , ( str ) => str . trim ( ) . includes ( str ) ) ) ; } ) ; } ) ;