1 Introduction

The Subplot library runcmd for Python provides scenario steps and their implementations for running Unix commands and examining the results. The library consists of a bindings file lib/runcmd.yaml and implementations in Python in lib/runcmd.py or in the Rust subplotlib step library. There is no Bash version.

This document explains the acceptance criteria for the library and how they’re verified. It uses the steps and functions from the lib/runcmd library. The scenarios all have the same structure: run a command, then examine the exit code, standard output (stdout for short), or standard error output (stderr) of the command.

The scenarios use the Unix commands true and false to generate exit codes, and echo to produce stdout. To generate stderr, they use the little helper script below.

#!/bin/sh
echo "$@" 1>&2

2 Check exit code

These scenarios verify the exit code. To make it easier to write scenarios in language that flows more naturally, there are a couple of variations.

2.1 Successful execution

2.2 Successful execution in a sub-directory

2.3 Failed execution

2.4 Failed execution in a sub-directory

3 Check we can prepend to $PATH

This scenario verifies that we can add a directory to the beginning of the PATH environment variable, so that we can have runcmd invoke a binary from our build tree rather than from system directories. This is especially useful for testing new versions of software that’s already installed on the system.

#!/bin/sh
echo "custom ls, not system ls"

4 Check output has what we want

These scenarios verify that stdout or stderr do have something we want to have.

4.1 Check stdout is exactly as wanted

Note that the string is surrounded by double quotes to make it clear to the reader what’s inside. Also, C-style string escapes are understood.

4.2 Check stderr is exactly as wanted

4.3 Check stdout using sub-string search

Exact string comparisons are not always enough, so we can verify a sub-string is in output.

4.4 Check stderr using sub-string search

4.5 Check stdout using regular expressions

Fixed strings are not always enough, so we can verify output matches a regular expression. Note that the regular expression is not delimited and does not get any C-style string escaped decoded.

4.6 Check stderr using regular expressions

5 Check output doesn’t have what we want to avoid

These scenarios verify that the stdout or stderr do not have something we want to avoid.

5.1 Check stdout is not exactly something

5.2 Check stderr is not exactly something

5.3 Check stdout doesn’t contain sub-string

5.4 Check stderr doesn’t contain sub-string

5.5 Check stdout doesn’t match regular expression

5.6 Check stderr doesn’t match regular expressions