NAME

SYNOPSIS

DESCRIPTION

GIVEN some setup for the test
WHEN thing that is to be tested happens
THEN the post-conditions must be true
    

As an example, consider a very short test scenario for verifying that a backup program works, at least for one simple case.

SCENARIO backups can be restored
GIVEN some live data in a directory
AND an empty backup repository
WHEN a backup is made
THEN the data case be restored
FINALLY cleanup
    

Note the addition of AND: you can have multiple GIVEN, WHEN, and THEN statements. The AND keyword makes the text be more readable. SCENARIO is also necessary, and gives the title.

FINALLY is for cleanups. The FINALLY steps will be run regardless of whether the scenario succeeds or not.

Scenarios are meant to be written in somewhat human readable language. However, they are not free form text. In addition to the GIVEN/WHEN/THEN structure, the text for each of the steps needs a computer-executable implementation. This is done by using IMPLEMENTS. The backup scenario from above might be implemented as follows:

IMPLEMENTS GIVEN some live data in a directory
rm -rf "$DATADIR/data"
mkdir "$DATADIR/data"
echo foo > "$DATADIR/data/foo"
    

IMPLEMENTS GIVEN an empty backup repository
rm -rf "$DATADIR/repo"
mkdir "$DATADIR/repo"
    

IMPLEMENTS WHEN a backup is made
backup-program -r "$DATADIR/repo" "$DATADIR/data"
    

IMPLEMENTS THEN the data can be restored
mkdir "$DATADIR/restored"
restore-program -r "$DATADIR/repo" "$DATADIR/restored"
diff -rq "$DATADIR/data" "$DATADIR/restored"
    

IMPLEMENTS FINALLY cleanup
echo nothing to do, actually
    

Each "IMPLEMENTS GIVEN" (or WHEN, THEN, FINALLY) is followed by a regular expression on the same line, and then a shell script that gets executed to implement any step that matches the regular expression. The implementation can extract data from the match as well: for example, the regular expression might allow a file size to be specified.

The above example is a bit silly, of course: why go to the effort to obfuscate the various steps? The answer is that the various steps, implemented using IMPLEMENTS, can be combined in many ways, to test different aspects of the program being tested.

Moreover, by making the step descriptions be human language text, matched by regular expressions, most of the test can hopefully be written, and understood, by non-programmers. Someone who understands what a program should do, could write tests to verify its behaviour. The implementations of the various steps need to be implemented by a programmer, but given a well-designed set of steps, with enough flexibility in their implementation, that quite a good test suite can be written.

The shell commands in an IMPLEMENTS section are run in the directory in which the user ran yarn. The environment variable SRCDIR is set to the fully qualified path to that directory.

OPTIONS

--allow-missing-steps

allow scenarios to reference steps that do not exist, by warning about them, but otherwise ignoring the scenarios

--no-allow-missing-steps

opposite of --allow-missing-steps

--cd-datadir

change to DATADIR when running commands

--no-cd-datadir

opposite of --cd-datadir

--env=NAME=VALUE

add NAME=VALUE to the environment when tests are run

--generate-manpage=TEMPLATE

fill in manual page TEMPLATE

-h, --help

show this help message and exit

--output=FILE

write output to FILE, instead of standard output

-q, --quiet

be quiet, avoid progress reporting, only show errors

--no-quiet

opposite of --quiet

--require-assumptions

require ASSUMING to always pass

--no-require-assumptions

opposite of --require-assumptions

-r, --run=SCENARIO

run only SCENARIO (this option can be repeated)

--shell=SHELL

run IMPLEMENTS using SHELL

--shell-arg=ARG

use ARG when running shell

-s, --shell-library=SHELL-LIBRARY

include a shell library for the IMPLEMENTS sections to use

--snapshot

make snapshots of test working directory after each scenario step; you probably want to use this with --tempdir

--no-snapshot

opposite of --snapshot

--stop-on-first-fail

stop if any scenario step fails, don't run more scenarios

--no-stop-on-first-fail

opposite of --stop-on-first-fail

--tempdir=DIR

use DIR as the temporary directory for tests; it should be empty or not exist

--timings

report wall clock time for each scenario and step

--no-timings

opposite of --timings

-v, --verbose

make progress reporting be more verbose ("wall of text"), instead of a one-line status info; this is turned automatically if there is not terminal

--no-verbose

opposite of --verbose

--version

show program's version number and exit

-n, --no-act, --dry-run, --pretend

do not actually run any tests, merely print what would be run

--no-no-act, --no-dry-run, --no-pretend

opposite of --no-act

ENVIRONMENT

DATADIR

Fully qualified pathname to a temporary directory, in which the tests can use files. The temporary directory is removed at the end of the test execution, unless the user specifies otherwise with --snapshot.

SRCDIR

Fully qualitifed pathname to the directory in which the user ran yarn. This is useful when the tests want to change the directory.

EXAMPLE

yarn *.scenario
    

All the files will be treated together as if they had been one file.

To add a shell library to be included when running any IMPLEMENTS section:

yarn --shell-library mylib.sh *.scenario
    

You can repeat --shell-library as many times as necessary.

SEE ALSO

The README.yarn file has more details on the scenario testing language.