What is MC/DC?
Modified Condition Decision Testing, Branch Condition Testing and Branch
Condition Combination Testing are closely related, as are the associated coverage measures.
Consider the following fragment of code:
The Boolean operands within the decision condition are A, B and C. These
may themselves be comprised of complex expressions involving relational operators. For
example, the Boolean operand A could be an expression such as X >= Y.
However, for the sake of clarity, the following examples regard A, B
and C as simple Boolean operands.
Understanding MC/DC
MC/DC is calculated using the following relationship:
It is a pragmatic compromise which requires fewer test cases than BCCC. It is
widely used in the development of avionics software, as required by the RTCA/DO-178B standard.
MC/DC requires test cases to show that each Boolean operand (A,
B and C) can independently affect the outcome of the decision. This is less
than all the combinations (as required by BCCC).
Example
For the example condition, MC/DC may be achieved with the following set of
test inputs (note that there are alternative sets of test inputs, which will also achieve MC/DC):
Case A B C Outcome
1 FALSE FALSE TRUE FALSE
2 TRUE FALSE TRUE TRUE
3 FALSE TRUE TRUE TRUE
4 FALSE TRUE FALSE FALSE
In the above example:
- A is shown to independently affect the outcome of the decision condition by
case 1 and case 2;
- B is shown to independently affect the outcome of the decision condition by
case 1 and case 3;
- C is shown to independently affect the outcome of the decision condition by
case 3 and case 4.
To achieve 100% MC/DC requires a minimum of n+l test cases, and a maximum of
2n test cases. It is therefore a practical compromise with Branch Condition Combination Coverage
where condition expressions involve more than just a few Boolean operands.
Measuring MC/DC with LDRA Testbed
The LDRA Testbed will display the following MC/DC Coverage results criteria:
- The list of Branch Conditions (BC) produced in the BC analysis to obtain
the Branch Condition Number.
- The table of Branch Condition Combinations (BCC) produced in the BCC
analysis to determine which combinations have been exercised.
The MC/DC analysis is presented for each expression listed at the foot
of the Branch Condition Coverage section of the Dynamic Coverage Analysis report.
Obtaining Further Information
For further information on this particular feature of TBsafe and its availability please complete the LDRA reply form or email .
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