`{.push overflowChecks: off.}` works in backends. Though it could be
implemented as a magic function.
By inspecting the generated C code, the overflow check is eliminated in
the debug or release mode.

Likewise, the index checking is probably not needed.
(cherry picked from commit d82bc0a29f)
Each test must have a filename of the form: t*.nim
Note:Testament is only aware of tests under a directory (eg tests/foo/) and will ignore
top-level tests like tests/tbar.nim.
Specs
Each test can contain a spec in a discard """ ... """ block.
Check out the parseSpec procedure in the specs module for a full and reliable reference
action
Specifies what action this test should take.
Default: run
Options:
compile - compiles the module and fails the test if compilations fails.
run - compiles and runs the module, fails the test if compilation or
execution of test code fails.
reject - compiles the module and fails the test if compilation succeeds.
There are certain spec keys that imply run, including output and
outputsub.
Categories
Each folder under this directory represents a test category, which can be
tested by running koch tests pcat <category> (or cat to avoid parallel
testing, which is slower).
The folder dll contains simple DLL tests.
The folder realtimeGC contains a test for validating that the realtime GC
can run properly without linking against the nimrtl.dll/so.