N this chapter, we will introduce you to the fundamentals of testing: why testing is
partitioning, with three-value boundaries. He makes a distinction between open
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partitioning, with three-value boundaries. He makes a distinction between open and closed boundaries, where a closed boundary is one where the point is included in the domain. So the convention is for the valid partition to have closed boundaries. You may be pleased to know that you don ’t have to know this for the exam! British Standard 7925 –2 Standard for Software Component Testing also defines a three- value approach to boundary value analysis. So which approach is best? If you use the two-value approach together with equivalence partitioning, you are equally effective and slightly more efficient than the three-value approach. (We won ’t go into the details here but this can be demonstrated.) In this book we will use the two-value approach. In the exam, you may have a question based on either the two-value or the three-value approach, but it should be clear what the correct choice is in either case. Designing test cases Having identified the conditions that you wish to test, in this case by using equivalence partitioning and boundary value analysis, the next step is to design the test cases. The more test conditions that can be covered in a single test case, the fewer test cases will be needed in order to cover all the conditions. This is usually the best approach to take for positive tests and for tests that you are reasonably confident will pass. However if a test fails, then we need to find out why it failed – which test condition was handled incorrectly? We need to get a good balance between covering too many and too few test conditions in our tests. Section 3 Specification-Based or Black-Box Techniques 87 Let ’s look at how one test case can cover one or more test conditions. Using the bank balance example, our first test could be of a new customer with a balance of $500. This would cover a balance in the partition from $100.01 to $999.99 and an output partition of a 5% interest rate. We would also be covering other partitions that we haven ’t discussed yet, for example a valid customer, a new customer, a customer with only one account, etc. All of the partitions covered in this test are valid partitions. When we come to test invalid partitions, the safest option is probably to try to cover only one invalid test condition per test case. This is because programs may stop processing input as soon as they encounter the first problem. So if you have an invalid customer name, invalid address, and invalid balance, you may get an error message saying ‘invalid input’ and you don’t know whether the test has detected only one invalid input or all of them. (This is also why specific error messages are much better than general ones!) However, if it is known that the software under test is required to process all input regardless of its validity, then it is sensible to continue as before and design test cases that cover as many invalid conditions in one go as possible. For example, if every invalid field in a form has some red text above or below the field saying that this field is invalid and why, then you know that each field has been checked, so you have tested all of the error processing in one test case. In either case, there should be separate test cases covering valid and invalid conditions. To cover the boundary test cases, it may be possible to combine all of the minimum valid boundaries for a group of fields into one test case and also the maximum boundary values. The invalid boundaries could be tested together if the validation is done on every field; otherwise they should be tested separately, as with the invalid partitions. Why do both equivalence partitioning and boundary value analysis? Technically, because every boundary is in some partition, if you did only boundary value analysis you would also have tested every equivalence partition. However, this approach may cause problems if that value fails – was it only the boundary value that failed or did the whole partition fail? Also by testing only boundaries we would probably not give the users much confidence as we are using extreme values rather than normal values. The boundaries may be more difficult (and therefore more costly) to set up as well. For example, in the printer copies example described earlier we identified the following boundary values: Invalid Valid Invalid 0 1 99 100 Suppose we test only the valid boundary values 1 and 99 and nothing in between. If both tests pass, this seems to indicate that all the values in between should also work. However, suppose that one page prints correctly, but 99 pages do not. Now we don ’t know whether any set of more than one page works, so the first thing we would do would be to test for say 10 pages, i.e. a value from the equivalence tải về 6.34 Mb. Chia sẻ với bạn bè của bạn:
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