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</v:background></xml><![endif]--><div class=WordSection1><p class=MsoNormal>I am having trouble figuring out how to write code that raises an argument error<o:p></o:p></p><p class=MsoNormal>and code that tests for that error using rackunit.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have the following function, which raises and exception when <o:p></o:p></p><p class=MsoNormal>pennies is negative, in a file:<o:p></o:p></p><p class=MsoNormal>-----------------------------------<o:p></o:p></p><p class=MsoNormal>#lang racket<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>(define (sum-coins pennies nickels dimes quarters )<o:p></o:p></p><p class=MsoNormal> (cond <o:p></o:p></p><p class=MsoNormal> [(negative? pennies) (raise-argument-error 'sum-coins "negative?" 0 pennies)<o:p></o:p></p><p class=MsoNormal> ])<o:p></o:p></p><p class=MsoNormal> (+ pennies (* 5 nickels) (* 10 dimes) (* 25 quarters)))<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>(provide sum-coins)<o:p></o:p></p><p class=MsoNormal>------------------------------<o:p></o:p></p><p class=MsoNormal>In a separate test file, I have the following test case:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>--------------------<o:p></o:p></p><p class=MsoNormal>#lang racket<o:p></o:p></p><p class=MsoNormal>(require rackunit "mybasic.rkt")<o:p></o:p></p><p class=MsoNormal> (test-exn "negative coin" negative? (sum-coins -1 3 5 7) )<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>---------------------<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>When I run the test, I get the following error:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>--------------------<o:p></o:p></p><p class=MsoNormal>negative coin<o:p></o:p></p><p class=MsoNormal>ERROR<o:p></o:p></p><p class=MsoNormal>. . sum-coins: contract violation<o:p></o:p></p><p class=MsoNormal> expected: negative?<o:p></o:p></p><p class=MsoNormal> given: -1<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>--------------------<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This is not what I expect. I expect the test to succeed if the argument error is raised.<o:p></o:p></p><p class=MsoNormal>I believe that there is something not quite correct about both the code that raises the exception<o:p></o:p></p><p class=MsoNormal>and the call that tests it. The examples in the Racket documentation online for raising an argument error<o:p></o:p></p><p class=MsoNormal>and for testing for the error/exception are not clear to me, obviously.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Can someone help?<o:p></o:p></p></div></body></html>