Acceptance criteria for the lib/runcmd Subplot library

The Subplot project

2021-10-21 11:32

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. 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.

File: err.sh

#!/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

when I run true
then exit code is 0
and command is successful

2.2 Successful execution in a sub-directory

given a directory xyzzy
when I run, in xyzzy, pwd
then exit code is 0
then command is successful
then stdout contains "/xyzzy"

2.3 Failed execution

when I try to run false
then exit code is not 0
and command fails

2.4 Failed execution in a sub-directory

given a directory xyzzy
when I try to run, in xyzzy, false
then exit code is not 0
and command fails

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.

given executable script ls from ls.sh
when I prepend . to PATH
when I run ls
then command is successful
then stdout contains "custom ls, not system ls"

File: ls.sh

#!/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.

when I run echo hello, world
then stdout is exactly "hello, world\n"

4.2 Check stderr is exactly as wanted

given helper script err.sh for runcmd
when I run sh err.sh hello, world
then stderr is exactly "hello, world\n"

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

when I run echo hello, world
then stdout contains "world\n"
and exit code is 0
given helper script err.sh for runcmd
when I run sh err.sh hello, world
then stderr contains "world\n"

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.

when I run echo hello, world
then stdout matches regex world$

4.6 Check stderr using regular expressions

given helper script err.sh for runcmd
when I run sh err.sh hello, world
then stderr matches regex world$

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

when I run echo hi
then stdout isn't exactly "hello, world\n"

5.2 Check stderr is not exactly something

given helper script err.sh for runcmd
when I run sh err.sh hi
then stderr isn't exactly "hello, world\n"

5.3 Check stdout doesn’t contain sub-string

when I run echo hi
then stdout doesn't contain "world"

5.4 Check stderr doesn’t contain sub-string

given helper script err.sh for runcmd
when I run sh err.sh hi
then stderr doesn't contain "world"

5.5 Check stdout doesn’t match regular expression

when I run echo hi
then stdout doesn't match regex world$

5.6 Check stderr doesn’t match regular expressions

given helper script err.sh for runcmd
when I run sh err.sh hi
then stderr doesn't match regex world$