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Cram: It's test time

Cram is a functional testing framework for command line applications based on Mercurial's unified test format.

Here's a snippet from cram.t in Cram's own test suite:

The $PYTHON environment variable should be set when running this
test from Python.

  $ [ -n "$PYTHON" ] || PYTHON=python
  $ if [ -n "$COVERAGE" ]; then
  >   coverage erase
  >   alias cram='coverage run -a'
  > else
  >   alias cram="$PYTHON"
  > fi
  $ command -v md5 || alias md5=md5sum


  $ cram -h
  [Uu]sage: cram \[OPTIONS\] TESTS\.\.\.

    -h, --help            show this help message and exit
    -v, --verbose         show filenames and test status
    -i, --interactive     interactively merge changed test output
    -y, --yes             answer yes to all questions
    -n, --no              answer no to all questions
    -D DIR, --tmpdir=DIR  run tests in DIR
    --keep-tmpdir         keep temporary directories
    -E                    don't reset common environment variables
  $ cram
  [Uu]sage: cram \[OPTIONS\] TESTS\.\.\.

The format in a nutshell:

  • Cram 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.
  • Command output in the test is first matched literally with the actual output. If it doesn't match, it's then compiled and matched as a Perl-compatible regular expression.
  • Command output in the test that ends with a percent sign will match actual output that doesn't end in a newline.
  • Anything else is a comment.



You can use pip to install Cram:

$ sudo pip install cram

Or you can install Cram the old fashioned way:

$ wget
$ tar zxvf cram-0.3.tar.gz
$ cd cram-0.3.tar.gz
$ sudo python install


Cram 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.

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

$ cram examples
--- examples/fail.t
+++ examples/fail.t.out
@@ -3,11 +3,11 @@
   $ echo 1
   $ echo 1
-  2
+  1
   $ echo 1

 Invalid regex:

   $ echo 1
-  +++
+  1

Cram will also write the test with its actual output to examples/fail.t.err.

When you're first writing a test, you might just write the commands and run the test to see what happens. If you run Cram 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.

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.
  • LANG, LC_ALL, and LANGUAGE are set to C.
  • TZ is set to GMT.
  • COLUMNS is set to 80.
  • CDPATH and GREP_OPTIONS are set to an empty string.

Cram also provides the following environment variables to tests:

  • RUNDIR, set to the directory Cram was run from.
  • TESTDIR, set to the test runner's temporary directory.


Version 0.3

  • Implemented resetting of common environment variables. This behavior can be disabled using the -E flag.
  • Changed the test runner to first make its own overall random temporary directory, make tmp inside of it and set TMPDIR, etc. to its path, and run each test with a random temporary working directory inside of that.
  • Added --keep-tmpdir. Temporary directories are named by test filename (along with a random string).
  • Added -i/--interactive to merge actual output back to into tests interactively.
  • Added ability to match command output not ending in a newline by suffixing output in the test with %.

Version 0.2

  • Changed the test runner to run tests with a random temporary working directory.

Version 0.1

  • Initial release.


Download the official development repository using Mercurial:

hg clone

Test Cram using Cram:

make tests

Get a test coverage report using

make coverage

Visit Bitbucket if you'd like to fork the project, watch for new changes, or report issues.