Prysk is a fork of the popular snapshot testing tool Cram. Even though Cram is pretty complete and mature for everyday use, Prysk wants to continue pushing its development forward.

Prysk tests look like snippets of interactive shell sessions. Prysk runs each command and compares the command output in the test with the command’s actual output.

Here’s a snippet from Prysk’s own test suite:

Set up prysk alias and example tests:

  $ . "$TESTDIR"/


  $ prysk -h
  [Uu]sage: prysk \[OPTIONS\] TESTS\.\.\. (re)

  [Oo]ptions: (re)
    -h, --help          show this help message and exit
    -V, --version       show version information and exit
    -q, --quiet         don't print diffs
    -v, --verbose       show filenames and test status
    -i, --interactive   interactively merge changed test output
    -d, --debug         write script output directly to the terminal
    -y, --yes           answer yes to all questions
    -n, --no            answer no to all questions
    -E, --preserve-env  don't reset common environment variables
    --keep-tmpdir       keep temporary directories
    --shell=PATH        shell to use for running tests (default: /bin/sh)
    --shell-opts=OPTS   arguments to invoke shell with
    --indent=NUM        number of spaces to use for indentation (default: 2)
    --xunit-file=PATH   path to write xUnit XML output
    --dos2unix          convert DOS/Windows line endings to UNIX line endings
    --color             mode which shall be used for coloring the output

The format in a nutshell:

  • Prysk tests use the .t file extension.

  • Lines beginning with two spaces, a dollar sign ($), and a space are run in the shell.

  • Lines beginning with two spaces, a greater than sign (>), and a space allow multi-line commands.

  • All other lines beginning with two spaces are considered command output.

  • Output lines ending with a space and the keyword (re) are matched as Perl-compatible regular expressions.

  • Lines ending with a space and the keyword (glob) are matched with a glob-like syntax. The only special characters supported are * and ?. Both characters can be escaped using \, and the backslash can be escaped itself.

  • Output lines ending with either of the above keywords are always first matched literally with actual command output.

  • Lines ending with a space and the keyword (no-eol) will match actual output that doesn’t end in a newline.

  • Actual output lines containing unprintable characters are escaped and suffixed with a space and the keyword (esc). Lines matching unprintable output must also contain the keyword.

  • Anything else is a comment.


Prysk will print a dot for each passing test. If a test fails, a unified context diff is printed showing the test’s expected output and the actual output. Skipped tests (empty tests and tests that exit with return code 80) are marked with s instead of a dot.

For example, if we run Prysk on its own example tests:

--- examples/fail.t
+++ examples/fail.t.err
@@ -3,21 +3,22 @@
   $ echo 1
   $ echo 1
-  2
+  1
   $ echo 1

 Invalid regex:

   $ echo 1
-  +++ (re)
+  1

 Offset regular expression:

   $ printf 'foo\nbar\nbaz\n\n1\nA\n@\n'
+  bar

   \d (re)
   [A-Z] (re)
-  #
+  @
# Ran 6 tests, 2 skipped, 1 failed.

Prysk will also write the test with its actual output to examples/fail.t.err, allowing you to use other diff tools. This file is automatically removed the next time the test passes.

When you’re first writing a test, you might just write the commands and run the test to see what happens. If you run Prysk with -i or --interactive, you’ll be prompted to merge the actual output back into the test. This makes it easy to quickly prototype new tests.

Is the same as invoking Prysk with --verbose and --indent=4.

Note that the following environment variables are reset before tests are run:

  • TMPDIR, TEMP, and TMP are set to the test runner’s tmp directory. In test output, occurrences of this directory are replaced by $TMPDIR.

  • LANG, LC_ALL, and LANGUAGE are set to C.

  • TZ is set to GMT.

  • COLUMNS is set to 80. (Note: When using --shell=zsh, this cannot be reset. It will reflect the actual terminal’s width.)

  • CDPATH and GREP_OPTIONS are set to an empty string.

Prysk also provides the following environment variables to tests:

  • PRYSK_TEMP, set to the test runner’s temporary directory.

  • TESTDIR, set to the directory containing the test file.

  • TESTFILE, set to the basename of the current test file.

  • TESTSHELL, set to the value specified by --shell.

Also note that care should be taken with commands that close the test shell’s stdin. For example, if you’re trying to invoke ssh in a test, try adding the -n option to prevent it from closing stdin. Similarly, if you invoke a daemon process that inherits stdout and fails to close it, it may cause Prysk to hang while waiting for the test shell’s stdout to be fully closed.