软件测试参考文献(9)

软件测试

DESIGN VERIFICATION

Simplifying the test set

The methodologies for adjusting the test set are using slid-ing levels and reducing (removing from the table) nonessen-

tial factor levels. Their purpose is to ful ll the test needs witha smaller set of tests—that is, a smaller orthogonal array.Let us consider an even more complex set of factors,which includes, in addition to the ones mentioned for ver-sion B, three levels of each radio band: AM, FM1, and FM2.Hence, for version C, the Radio factor has 10 levels: threeAMs, three FM1s, three FM2s, and Off. Table 9 shows the fac-tor table with the associated values and their levels.

Now the minimum number of tests is Tmin= MAX(Nfr, Ph)= 30, where Nfr= 1 + 2 ×(2 1)+3 ×(3 1)+1 ×(10 1) =18 and Ph= 10 ×3 = 30.

To reduce the number of tests below 30, we use the slid-ing-level technique. With this technique, we cover the Radiofactor using two factors each with fewer levels. One factordetermines the band (am, fm1, fm2, or Off), and the otherdetermines the wavelengths inside the band. For example,to combine Radio = FM1 and Radio level = 2 in the orthog-onal table, we select FM1 for the test and 95.5 for the wave-length. Table 10 (next page) represents the modified Cversion of the audio factor set.

For the modi ed factors de nition, Tmin= MAX(Nfr, Ph) =14, where Nfr= 1 + 4 ×(3 1) + 2 ×(2 1) + 1 ×(4 1) = 14and Ph= 3 ×4 = 12.

Hence, we must look for a table that can accommodatetwo 2-level factors, four 3-level factors, and one 4-level fac-tor. L18meets this condition perfectly, in spite of the increasein state count. Table 11 contains the resulting test set. In thiscase, we use column 8 for the wavelength definition.Column 2 could be used instead of column 8 with the sameeffectiveness. For a better understanding of the transforma-tion, we added a column to the right of the table to showthe previously existing generic values in column 8.

Another way of reducing the test set is by analyzing theimportance of testing all the different state combinations. Ifnot all of them need testing, we can directly reduce the testset. If all are important, we can split the tests into severalsmaller sets.

For example, we may decide that testing two wavelength

58IEEE DESIGN & TEST OF COMPUTERS

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