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Hacker Professional Ebook part 179

Tham khảo tài liệu 'hacker professional ebook part 179', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | It is now easy to construct large hardware or software systems which are almost unmanageably complex and never error-free. But a good design and development approach can produce systems with far fewer problems. One such approach is 1. Decompose the system into small testable components. 2. Construct and then actually test each of the components individually. This is both easier and harder than it looks there are many ways to decompose a large system and finding an effective and efficient decomposition can take both experience and trial-and-error. But many of the possible decompositions define components which are less testable or even untestable so the testability criterion greatly reduces the search. Testing is no panacea we cannot hope to find all possible bugs this way. But in practice we can hope to find 90 percent or more of the bugs simply by actually testing each component. Component testing means that we are forced to think about what each component does and about its requirements and limits. Then we have to make the realized component conform to those tests which were based on our theoretical concepts. This will often expose problems whether in the implementation the tests or the concepts. By testing all components when we put the system together we can hope to avoid having to debug multiple independent problems simultaneously. Other important system design concepts include Build in test points and switches to facilitate run-time inspection control and analysis. Use repeatable comprehensive tests at all levels and when a component is fixed run those tests again. Start with the most basic system and fewest components make that work pass appropriate system tests then add features one-by-one. Try not to get too far before making the expanded system work again. Table Selection Combiner A combining mechanism in which one input selects a table or substitution alphabet and another input selects a value from within the selected table said value becoming the .