|YARN(1)||General Commands Manual||YARN(1)|
yarn - scenario testing of Unix command line tools
yarn [--allow-missing-steps] [--no-allow-missing-steps] [--cd-datadir] [--no-cd-datadir] [--config=FILE] [--dump-config] [--dump-setting-names] [--generate-manpage=TEMPLATE] [-h] [--help] [--help-all] [--list-config-files] [--version] [--no-default-configs] [--dump-memory-profile=METHOD] [--env=NAME=VALUE] [--log=FILE] [--log-keep=N] [--log-level=LEVEL] [--log-max=SIZE] [--log-mode=MODE] [--memory-dump-interval=SECONDS] [--output=FILE] [-q] [--quiet] [--no-quiet] [--require-assumptions] [--no-require-assumptions] [-rSCENARIO] [--run=SCENARIO] [--shell=SHELL] [--shell-arg=ARG] [-sSHELL-LIBRARY] [--shell-library=SHELL-LIBRARY] [--snapshot] [--no-snapshot] [--stop-on-first-fail] [--no-stop-on-first-fail] [--tempdir=DIR] [--timings] [--no-timings] [-v] [--verbose] [--no-verbose] [-n] [--no-act] [--dry-run] [--pretend] [--no-no-act] [--no-dry-run] [--no-pretend] [FILE]...
yarn is a scenario testing tool: you write a scenario describing how a user uses your software and what should happen, and express, using very lightweight syntax, the scenario in such a way that it can be tested automatically. The scenario has a simple, but strict structure:
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.
- allow scenarios to reference steps that do not exist, by warning about them, but otherwise ignoring the scenarios
- opposite of --allow-missing-steps
- change to DATADIR when running commands
- opposite of --cd-datadir
- add NAME=VALUE to the environment when tests are run
- fill in manual page TEMPLATE
- -h, --help
- show this help message and exit
- write output to FILE, instead of standard output
- -q, --quiet
- be quiet, avoid progress reporting, only show errors
- opposite of --quiet
- require ASSUMING to always pass
- opposite of --require-assumptions
- -r, --run=SCENARIO
- run only SCENARIO (this option can be repeated)
- run IMPLEMENTS using SHELL
- use ARG when running shell
- -s, --shell-library=SHELL-LIBRARY
- include a shell library for the IMPLEMENTS sections to use
- make snapshots of test working directory after each scenario step; you probably want to use this with --tempdir
- opposite of --snapshot
- stop if any scenario step fails, don't run more scenarios
- opposite of --stop-on-first-fail
- use DIR as the temporary directory for tests; it should be empty or not exist
- report wall clock time for each scenario and step
- 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
- opposite of --verbose
- 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
Configuration files and settings¶
- write log entries to FILE (default is to not write log files at all); use "syslog" to log to system log, "stderr" to log to the standard error output, or "none" to disable logging
- keep last N logs (10)
- log at LEVEL, one of debug, info, warning, error, critical, fatal (default: debug)
- rotate logs larger than SIZE, zero for never (default: 0)
- set permissions of new log files to MODE (octal; default 0600)
- 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.
- Fully qualitifed pathname to the directory in which the user ran yarn. This is useful when the tests want to change the directory.
To run yarn on all the scenarios in your current directory:
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.
The README.yarn file has more details on the scenario testing language.