The purpose of dynamic variables is to support
"variant" testing, where a script can loop over a test multiple times,
changing the variable to different values.

Dynamic variables are expanded to full variables names that are prefixed
with the name of the test, during test execution.  A dynamic variable
overrides a spec variable of the same name.

Here is an example of using dynamic variables:

{{{#!YellowBox
 $ ftc run-test -b beaglebone -t Benchmark.Dhrystone --dynamic-vars "LOOPS=100000000"
}}}

This would override the default value for BENCHMARK_DHRYSTONE_LOOPS,
setting it to 100000000 (100 million) for this run.  Normally, the
default spec for Benchmark.Dhrystones specifies a value of 10000000
(10 million) for LOOPS.

This feature is intended to be useful for doing 'git bisect's of
a bug, passing a different git commit id for each iteration of the test.

See [[Test_variables]] for more information.

== Notes ==
Note that dynamic vars are added to the runtime spec.json file, which is
saved in the log directory for the run being executed.

This spec.json file is copied from the one specified for the run (usually
from the test's home directory).

If dynamic variables have been defined for a test, then they are listed
by name in the run-specific spec.json file, as the value of the variable
"dyn_vars".  The reason for this is to allow someone who reviews the test
results later to easily see whether a particular test variable had a
value that derived from the spec, or from a dynamic variable.  This is
important for proper results interpretation.