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Subshell_Testing.md

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Sub-Shell Testing

To test a command which runs another command the usual approach is to have a helper script and supply that as the subcommand. If the subcommand script should be able to perform its own assertions it'll have to include the assert.sh file by itself (its full path is available in the $ASSERTSH env var).

The test framework offers the prepare_subshell() function to aid this process: it will create a new, randomly-named script file, fill it with some initialization calls, and append its stdin input.

Initialization done by all subshell scripts created by prepare_subshell():

  1. Sets env var $IN_SUBSHELL=yes,
  2. creates a randomized marker file so that assertSubshellWasExecuted() will succeed,
  3. includes the assert.sh script so that all assertion functions as well as fail() and err() are available,
  4. redefines cleanup() and success() as they should not do anything inside a subshell,
  5. includes the config.sh script (if it exists).

The filname of the new script file is stored in the $TMPSH and $SHELL env vars. This can be useful to test commands which don't take a subcommand argument but simply start a new interactive shell.

prepare_subshell() requires a prior cd_tmpdir() call, because it'll refuse to create the subshell script in the test root.

Example

This test script tests whether bash is installed, whether bash supports the -c option to run arbitrary commands, and whether bash correctly increments the $SHLVL counter by 1.

#!/bin/sh
. $(dirname "$0")/init.sh

export SHLVL=1

cd_tmpdir
prepare_subshell <<EOT
  assertEq "\$SHLVL" 2  "bash executed the subshell script, but did not correctly increment the SHLVL counter!"
EOT

# The subshell script's filename is now stored in $TMPSH.
# Try to run 'bash -c subshell', verify that it terminates with exit status zero.
assertCmd "bash -c $TMPSH"

# If 'bash -c' did not actually work correctly but still exited with a zero status,
# then assertCmd() did not notice anything amiss.
# Verify that the subshell script has been executed at least once:
assertSubshellWasExecuted

success