Example of Multicondition coverage (Multiple condition coverage - MCC)

Simple example

Assume we want to test the following code extract:

if ( (A || B) && C )
{
/* instructions */
}
else
{
/* instructions */
}

where A, B and C represent atomic boolean expressions (i.e. not divisible in other boolean sub-expressions).

In order to ensure Multicondition coverage criteria for this example, each combination of values for A, B and C should be tested at least one time.

So, in our example, we need 2³=8 testes leading to the following evaluations of A, B and C to valid Multicondition coverage:

1. A = true  / B = true  / C = true
2. A = true  / B = true  / C = false
3. A = true  / B = false / C = true
4. A = true  / B = false / C = false
5. A = false / B = true  / C = true
6. A = false / B = true  / C = false
7. A = false / B = false / C = true
8. A = false / B = false / C = false

However, Testwell CTC++ used to ensure Multicondition coverage ("-i m" option of instrumentation) will present the results of testes in the following way:

1. A = true  / B = not eval / C = true
2. A = true  / B = not eval / C = false
3. A = false / B = true       / C = true
4. A = false / B = true       / C = false
5. A = false / B = false      / C = not eval

E.g., for the 1^st case, if A is "true", system will not calculate the value of B since in every way (A or B) will be evaluated to "true". In fact, it means that the 1^st and 2^nd cases of the 1^st list will be evaluated in the same way by the system and that Testwell CTC++ will follow this logic while presenting the results.

More complex example

Assume we replace the condition: ( (A || B) & C )
by: ( ((u == 0) || (x>5)) & ((y<6) || (z == 0)) )

A full Test Coverage would consist into building the following truth table and testing each combination:

And to ensure a full Multicondition coverage, we should test each combination, i.e. the 9 possible testes here-before underlined in yellow.

Go back to Test Coverage Levels

Glossary:

Condition: a logical indivisible (atomic) expression. It is often called boolean variable, represented by a capital letter (A, B, C, etc.), can only be equal to "true" or "false", but can not be divided in other simpler "sub-conditions".

Decision : a logical expression which can be composed of several conditions separated by logical operators like "or", "and", "xor".

The Test Coverage Analyzer Testwell CTC++ can do measurements for all kinds of test coverage criteria (particularly for MC/DC and MCC) requested for "critical software development" in order to get certifications, such as DO-178B of the Federal Aviation Administration (FAA).

last updated: 03.08.2010

© 2010 Verifysoft Technology GmbH
Author: Christophe Sourisse, Verifysoft Technology GmbH
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