Importing functions from a shell script

I have a shell script that I would like to test with shUnit. The script (and all the functions) are in a single file since it makes installation much easier.

Example for script.sh

#!/bin/sh

foo () { ... }
bar () { ... }

code

I wanted to write a second file (that does not need to be distributed and installed) to test the functions defined in script.sh

Something like run_tests.sh

#!/bin/sh

. script.sh

# Unit tests

Now the problem lies in the . (or source in Bash). It does not only parse function definitions but also executes the code in the script.

Since the script with no arguments does nothing bad I could

. script.sh > /dev/null 2>&1

but I was wondering if there is a better way to achieve my goal.

Edit

My proposed workaround does not work in the case the sourced script calls exit so I have to trap the exit

#!/bin/sh

trap run_tests ERR EXIT

run_tests() {
   ...
}

. script.sh

The run_tests function is called but as soon as I redirect the output of the source command the functions in the script are not parsed and are not available in the trap handler

This works but I get the output of script.sh:

#!/bin/sh
trap run_tests ERR EXIT
run_tests() {
   function_defined_in_script_sh
}
. script.sh

This does not print the output but I get an error that the function is not defined:

#!/bin/sh
trap run_tests ERR EXIT
run_tests() {
   function_defined_in_script_sh
}
. script.sh | grep OUTPUT_THAT_DOES_NOT_EXISTS

This does not print the output and the run_tests trap handler is not called at all:

#!/bin/sh
trap run_tests ERR EXIT
run_tests() {
   function_defined_in_script_sh
}
. script.sh > /dev/null

According to the “Shell Builtin Commands” section of the bash manpage, . aka source takes an optional list of arguments which are passed to the script being sourced. You could use that to introduce a do-nothing option. For example, script.sh could be:

#!/bin/sh

foo() {
    echo foo $1
}

main() {
    foo 1
    foo 2
}

if [ "${1}" != "--source-only" ]; then
    main "${@}"
fi

and unit.sh could be:

#!/bin/bash

. ./script.sh --source-only

foo 3

Then script.sh will behave normally, and unit.sh will have access to all the functions from script.sh but will not invoke the main() code.

Note that the extra arguments to source are not in POSIX, so /bin/sh might not handle it—hence the #!/bin/bash at the start of unit.sh.