# Wrap executables run by tests¶

Avocado allows the instrumentation of executables being run by a test in a transparent way. The user specifies a script (“the wrapper”) to be used to run the actual program called by the test.

If the instrumentation script is implemented correctly, it should not interfere with the test behavior. That is, the wrapper should avoid changing the return status, standard output and standard error messages of the original executable.

The user can be specific about which program to wrap (with a shell-like glob), or if that is omitted, a global wrapper that will apply to all programs called by the test.

## Usage¶

This feature is implemented as a plugin, that adds the –wrapper option to the Avocado run command. For a detailed explanation, please consult the Avocado man page.

Example of a transparent way of running strace as a wrapper:

#!/bin/sh
exec strace -ff -o $AVOCADO_TEST_LOGDIR/strace.log --$@


To have all programs started by test.py wrapped with ~/bin/my-wrapper.sh:

$scripts/avocado run --wrapper ~/bin/my-wrapper.sh tests/test.py  To have only my-binary wrapped with ~/bin/my-wrapper.sh: $ scripts/avocado run --wrapper ~/bin/my-wrapper.sh:*my-binary tests/test.py


## Caveats¶

• It is not possible to debug with GDB (–gdb-run-bin) and use wrappers (–wrapper) at the same time. These two options are mutually exclusive.
• You can only set one (global) wrapper. If you need functionality present in two wrappers, you have to combine those into a single wrapper script.
• Only executables that are run with the avocado.utils.process APIs (and other API modules that make use of it, like mod:avocado.utils.build) are affected by this feature.