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README for story testing
========================
Introduction
------------
`story-test` is a story testing tool: you write a story describing
how a user uses your software and what should happen, and express,
using very lightweight syntax, the story in such a way that it can
be tested automatically. The story 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 story for verifying that
a backup program works, at least for one simple case.
GIVEN some live data in a directory
AND an empty backup repository
WHEN a backup is made
THEN the data case be restored
(Note the addition of AND: you can have multiple GIVEN, WHEN, and
THEN statements.)
Stories 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 story
from above might be implemented as follows:
IMPLEMENTS GIVEN some live data in a directory
rm -rf "$TESTDIR/data"
mkdir "$TESTDIR/data"
echo foo > "$TESTDIR/data/foo"
IMPLEMENTS GIVEN an empty backup repository
rm -rf "$TESTDIR/repo"
mkdir "$TESTDIR/repo"
IMPLEMENTS WHEN a backup is made
backup-program -r "$TESTDIR/repo" "$TESTDIR/data"
IMPLEMENTS THEN the data can be restored
mkdir "$TESTDIR/restored"
restore-program -r "$TESTDIR/repo" "$TESTDIR/restored"
diff -rq "$TESTDIR/data" "$TESTDIR/restored"
Each "IMPLEMENT GIVEN" (or WHEN, THEN) 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 an amount 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.
Test language specification
---------------------------
A test document is written in [Markdown][markdown], with block
quoted code blocks being interpreted specially. Each block
must follow the syntax defined here.
* Every step in a story is one line, and starts with a keyword.
* Each implementation (IMPLEMENTS) starts as a new block, and
continues until there is a block that starts with another
keyword.
The following keywords are defined.
* **STORY** starts a new story. The rest of the line is the name of
the story. The name is used for documentation and reporting
purposes only and has no semantic meaning. STORY MUST be the
first keyword in a story, with the exception of IMPLEMENTING.
A test document any number of stories, but must contain at least
one. The IMPLEMENTING sections are shared between them.
* **ASSUMING** defines a condition for the story. The rest of the
line is "matched text", which gets implemented by an
IMPLEMENTING section. If the code executed by the implementation
fails, the story is skipped.
* **GIVEN** prepares the world for the test to run. If
the implementation fails, the story fails.
* **WHEN** makes the change to the world that is to be tested.
If the code fails, the story fails.
* **THEN** verifies that the changes made by the GIVEN steps
did the right thing. If the code fails, the story fails.
* **FINALLY** specifies how to clean up after a story. If the
code fails, the story fails. The code gets run at the end of
the story, regardless of whether the story is failing or not.
* **AND** acts as ASSUMING, GIVEN, WHEN, THEN, or FINALLY: whichever
was used last. It must not be used unless the previous step was
one of those, or another AND.
* **IMPLEMENTING** is followed by one of ASSUMING, GIVEN, WHEN, or
THEN, and a PCRE regular expression, and then shell commands until
the end of the block quoted code block. Markdown is unclear whether
an empty line (no characters, not even whitespace) between two
block quoted code blocks starts a new one or not, so we resolve the
ambiguity by specifiying that the next code block is a continuation
unless it starts with one of the story testing keywords.
The shell commands get parenthesised parts of the match of the
regular expression as positional arguments (`$1` etc). For
example, if the regexp is "a (\d+) byte file", then `$1` gets
set to the number matchec by `\d+`.
The test runner creates a temporary directory, whose name is
given to the shell code in the `TESTDIR` environment variable.
The shell commands get invoked with `/bin/sh -eu`, and need to
be written accordingly. Be careful about commands that return
a non-zero exit code.
The code block of an IMPLEMENTING block fails if the shell
invocation exits with a non-zero exit code. Output to stderr is
not an indication of failure. Any output to stdout or stderr may
or may not be shown to the user.
Semantics:
* The name of each story (given with STORY) must be unique.
* Every ASSUMING, GIVEN, WHEN, THEN, FINALLY must be matched by
exactly one IMPLEMENTING. The test runner checks this before running
any code.
* Every IMPLEMENTING must match at least one ASSUMING, GIVNE, WHEN,
THEN, or FINALLY. The test runner checks this before running
any code.
* If ASSUMING fails, that story is skipped, and any FINALLY steps
are not run.
See also
--------
Wikipedia has an article on [Behaviour Driven Development][BDD],
which can provide background and further explanation to what this
tools tries to do.
[BDD]: https://en.wikipedia.org/wiki/Behavior-driven_development
[Markdown]: ...
TODO
----
* Add FINALLY to clean up at the end, regardless of test failures.
* Add DEFINING, PRODUCING, if they turn out to be useful.
* Need something like ASSUMING, except fail the story if the
pre-condition is not true. Useful for testing that you can ssh
to localhost when flinging, for example.
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