Multiple Condition Coverage (MCC)

MCC Metric Definition

In the MCC coverage metric, all statements must be executed and all combinations of truth values in each decision must occur at least once to reach full coverage. The coverage of a program is the number of executed statement blocks and condition combinations divided by their total number in the program.

Example

A C/C++ function with a decision based on a composed set of conditions nicely shows the difference between MCC and plain Condition Coverage:

bool isValidPosition(int x, int y, int z)
{
    if ((x > 10 || y > 20) && z > 0)
        return true;
    else
        return false;
}

For 100% MCC all combinations of truth values for the tree boolean expressions x > 10, y > 20 and z > 0 need to be exercised. One might expect 23 = 8 tests to be needed. Languages like C, C++, C# and JavaScript perform a so called short-circuit evaluation: If x > 10 evaluates to TRUE the expression y > 20 won’t be evaluated anymore. Likewise, if neither x > 10 nor y > 20 is TRUE z > 0 won’t be valuated anymore as it cannot change the decision anymore.

As a result the number of possible combinations and number of needed tests for 100% Multiple Condition Coverage is reduced to these five: