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【正文】 ance,a performance test of the bank account package evaluates the speed with which calculations are made,the precision fo the putation,the security precautions required,and the response time to user inquiry. At this point,the system operates the way the designers call this a verified system。that is,that the programmers wrote code to do what the designers system testing,we have a very different objective:to ensure that the system does what the customer wants it to understand how to meet this objective,we first must understand where faults in the system e from. Recall that a software fault causes a failure only when acpanied by the right is,a fault may exist in the code,but if the code is never executed,or if the code is not executed long enough or in the appropriate configuration to cause a problem,we may never see the software testing cannot exercise every possible condition,we keep as our goal the discovery of faults,hoping that in the process we eliminate all faults that might lead to failures during actual system usage. Software faults can be inserted in a requirement,design,or code ponent,or in the documentation,at any point during development or illustrates the likely causes of faults in each development we would like to find correct faults as early as possible,system testing acknowledges that faults may still be present after integration testing. Faults can be introduced to the system early in development or late,such as when correcting a newly discovered example,defective software can result from faults in the a requirement was ambiguous because the customer was unsure of a need or because we misinterpreted the customer’s meaning,the result is the same:a system that does not work the way the customer wants in to work. The same kind of munication mishaps can occur during system may misinterpret a requirement and write an incorrect design we understand the requirement but may word the specification so poorly that those who subsequently read it and use the design misunderstand ,we may make assumptions about characteristics and relationships that are not shared by the other readers of the design. Similar events can lead to program design are mon when the system design is translated into lowerlevel description for program design are several levels removed from the initial discussions with customers about system goals and responsibility for one “tree” but not the “forest,” programmers cannot be expected to spot design faults that have been perpetuated through the first steps of the development this reason,requirements and design reviews are essential to ensuring the quality of the resulting system. The programmers and designers on our development team may also fail to use the proper syntax and semantics for recording their piler or assembler can catch some fo these faults before a program
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