Step runner

When working with mocks, you would have to setup a mock for each command call with the expected argument numbers, return value, possible output and an index of the call.

Then, you would run the code to be tested and run assertions for each of the mocked commands.

For large scripts maintaining both parts becomes a tedious task.

This helper allows to setup and process a sequence of string and mocked command assertions. It helps to make maintenance of complex tests easier.

Consider this example:

 # Declare STEPS as a global variable, as `process_steps` needs to be called
 # twice and it does not store the steps internally.
 declare -a STEPS=(
   # Mock `drush` binary with an exit status of 1 and no output.
   "@drush -y status --field=drupal-version # 1"
   # Mock `drush` binary with an exit status of 0 and output "success".
   "@drush -y status --fields=bootstrap # success"
   # Mock `drush` binary with an exit status of 1 and output "failure".
   "@drush -y status --fields=bootstrap # 1 # failure"
   # Assert presence of the partial string in the output "Hello world"
   "Hello world"
   # Assert absence of the partial string in the output "Goodbye world"
   "- Goodbye world"
 )

 # Setup phase.
 mocks="$(process_steps "setup")" # $mocks will hold created mocks

 # ... code to be tested ...

 # Assert phase.
 process_steps "assert" "$mocks" # Assertions will be performed.

Every step is a string that can be one of the following:

@<command> [<args>] # <mock_status> [ # <mock_output> ]

Mock the command <command> with the given status and optional output.
Status can be omitted and <mock_output> can be used instead.
Different commands can be mocked multiple times.
Call to the same command will be using the same mock.

<substring>

Check that the output contains the given substring.

- <substring>

Ensure the output does NOT contain the specified substring. Starts with - (minus followed by space).