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To see the need for the Testcover.com service, consider a test system with five test factors and their values as follows.
| Test Factor | Number of Values | Test Factor Values |
|---|
| 1. Operating system | 4 | WXP OSX10 LNX9 WME |
|---|
| 2. Display resolution | 3 | low medium high |
|---|
| 3. Connection | 4 | dial-up dsl cable lan |
|---|
| 4. Browser | 4 | IE6 NS7 MZL1.5 IE5 |
|---|
| 5. Application | 3 | App1 App2 App3 |
|---|
The question is how to select test cases to cover the test factor values.
A simple approach is to pick one most common value for each test factor.
Then the tester varies each factor through all of its values
while holding the others at their most common values.
This example would lead to
4 + 3 + 4 + 4 + 3 = 18
test cases because there are 18 individual values to be covered.
(The tester may note that the test case with all factors at their
most common values is included five times and may remove four of these
test cases.)
The number of test cases here is relatively small, but their ability to find faults is limited.
While all of the values have been covered, all of the value pairs have not.
Thus, problems related to interactions between two factors may not be found.
A more ambitious approach is to test all combinations of factor values.
In this example there would be
4 • 3 • 4 • 4 • 3 = 576
test cases.
This method should find all the faults from interactions among these factors
because all combinations are tested.
Generally however, the method is not practical because it leads to too many test cases.
The need then is to find a small set of test cases which will include all factor value pairs.
Testers have used orthogonal arrays and covering arrays to select test cases when such arrays
are known to fit their test experiments.
These arrays are mathematical constructs which can have the desired coverage properties for the
factor value combinations.
Their use can improve a test program's efficiency and ability to find faults
compared to the methods described above.
But when real-world requirements are applied, the test design can become more complicated.
Suppose one of the planned test cases in this example is
Also suppose that browser IE5 is not supported on operating system LNX9.
That is, the test cases must be constrained not to include IE5 with LNX9.
What is to be done with the
test case?
It may fail if executed, or it may not be possible to run at all.
Removing the test case from the plan may reduce coverage of other
factor value pairs which are allowed (IE5 with high, for example).
The tester might decide to replace one of the values in the test case to make it possible.
NS7 could replace IE5 if NS7 is compatible with LNX9.
Then the test case
would appear in the plan instead.
But such a change also could reduce coverage for other pairs:
IE5 is not associated with high in this test case any more.
The Testcover.com service is designed to handle these types of test constraints easily.
The three examples below illustrate its use in common test situations.
| • The Configuration Example shows how to
generate test cases for a similar test system with five test factors.
No constraints are applied in this simple example. |
| • The Constraints Example shows how to
generate test cases for the test system described in this section.
The constraints among the browsers and operating systems are easily handled. |
| • Lastly the Calendar Example illustrates how to
generate error test cases along with those for normal operation. |
|
