When planning the basic path testing plan of the new taximeter module, Softw

9 When planning the basic path testing plan of the new taximeter module, Softw

a flow chart and a program flow graph for the taxi fare calculation process were prepared. Each figure represents a calculation process that includes five

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decisions, as shown in Figure 9.3.

A review of the ITS flow chart and program flow graph demonstrates the difference between path testing and basic path testing as well as com-

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paring the testing requirements of path coverage with those of line coverage. As mentioned above, full path coverage requires that all the possible paths be executed at least once. In the ITS flow chart (Figure 9.3), 24 differ- ent paths may be indicated. In other words, in order to achieve full path

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coverage of the software module we have to prepare at least 24 test cases, which we list in Table 9.3.

Table 9.3: The Imperial Taxi example – the full list of paths No.

The path 1 1-2-3-5-6-8-9-11-12-17

2 1-2-3-5-6-8-9-11-13-14-15-17 3 1-2-3-5-6-8-9-11-13-14-16-17 4 1-2-3-5-6-8-10-11-17 5 1-2-3-5-6-8-10-11-13-14-15-17 6 1-2-3-5-6-8-10-11-13-14-16-17 7 1-2-3-5-7-8-9-11-12-17 8 1-2-3-5-7-8-9-11-13-14-15-17 9 1-2-3-5-7-8-9-11-13-14-16-17 10 1-2-3-5-7-8-10-11-12-17 11 1-2-3-5-7-8-10-11-13-14-15-17 12 1-2-3-5-7-8-10-11-13-14-16-17 13 1-2-4-5-6-8-9-11-12-17 14 1-2-4-5-6-8-9-11-13-14-15-17 15 1-2-4-5-6-8-9-11-13-14-16-17 16 1-2-4-5-6-8-10-11-12-17 17 1-2-4-5-6-8-10-11-13-14-15-17 18 1-2-4-5-6-8-10-11-13-14-16-17 19 1-2-4-5-7-8-9-11-12-17 20 1-2-4-5-7-8-9-11-13-14-15-17 21 1-2-4-5-7-8-9-11-13-14-16-17 22 1-2-4-5-7-8-10-11-12-17 23 1-2-4-5-7-8-10-11-13-14-15-17 24 1-2-4-5-7-8-10-11-13-14-16-17

1 (a) Flow chart of the module

Charge the minimal fare

9.4 White bo

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WT ⬎ 3

5 WT ⱕ 3

ting

Waiting time

S⬎ 1

8 S ⱕ1

No. of suitcases

Regular client?

12 Yes

14 No

Night journey? 15 16

17 Print receipt

3 R1 4

(b) Program flow graph of the 6 7 module

Figure 9.3: The ITS taxi fare calculation process – flow chart and program flow graph

194 In contrast, the program flow graph allows us to observe that full line coverage of the ITS software module can be reached by inspecting the mini-

9 mum number of paths – a total of three – as listed in Table 9.4. Softw

The proportion of test cases required to test the system by full line cov- erage of three test cases (by basic path testing) versus full path coverage of

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24 test cases is 1:8! This ratio grows rapidly with program complexity. Support for the basic path testing strategy is provided by McCabe’s cyclomatic complexity metrics, which besides being software complexity

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metrics also serve to give an upper limit to the number of test cases needed for full line coverage.