Google Test allows to instantiate tests for a list of different values, which
are called parameters. A common use of that feature in Ardupilot will be that a
parameter will be represented by an object that will have the value to be
tested and information about that value. That information will basically map
the expected behavior of tests on the value stored by the parameter.
The macro added in this patch allows to easily print the value of a failed
test's parameter.
It was implemented in such a way that gtest is required only if the user wants
to build and run tests. Initially we're considering all tests should be gtests.
We can change that assumption in the future if necessary.
Gustavo Jose de Sousa