This page is about the darcs test suite.

Overview of types of tests

Darcs has tests in two formats. Unit tests that directly test Haskell functions are written in Haskell and live in modules under src/Darcs/Test. Functional tests that test the darcs binary are written as Bash shell scripts and live in tests/.

Haskell tests

These are QuickCheck and HUnit tests primarily testing the Darcs core. The Haskell modules containing these tests are under Darcs.Test in the module hierarchy. They are called from src/unit.lhs using the test-framework package from Hackage.

More about the Haskell tests can be found on the Unit Tests page.

Shell tests

Shell tests are useful because they are easy to create from a copy/paste of actual shell commands executed. They are considered successful if no bad exit codes are returned from the commands in the script. If the name of the script file starts with ‘failing-’ however, the script is expected to return a bad exit code. If such a script returns a bad exit code, this will not be treated as a test suite failure. This is useful to document bugs and to-do items.

Contributing a test to Darcs as a shell script

Contributing a test to Darcs is easy– no Haskell is required, just a bash shell script which you can base on the actual commands you used to trigger an issue.

Here’s how to get started:

darcs clone --lazy
cp tests/ tests/
# edit away
darcs record
darcs send

Regression tests are just shell scripts that fail on the first command that returns with a non-zero exit status (nb: exit 200 is special, see below)

See tests/ to get a template for writing these tests. Note also the tests/lib for things you should be able to invoke from your test or tests/ for little tricks you can copy and paste.

NB. If you’re not actually expecting your test to fail, then remove ‘failing-’ from the name.

Tips for writing a darcs test as a shell script

  • Name your patch Accept issueNNNN: (short description)
  • Just let darcs send do the thinking (no arguments or flags needed). The darcs repository will automatically specify what email address to send the patch to (one which will cause a patch tracker ticket to be created for your patch).
  • Exit status 200 gets special treatment; you can use it to skip tests that aren’t appropriate for a particular situation (for example they only make sense in darcs-2 repos and not darcs-1 repos)

Things to avoid to keep your shell scripts portable

  1. cp -a (BSD)
  2. sed -r (BSD)
  3. sed -i (BSD)
  4. yes | (doesn’t terminate on OpenBSD when SIGPIPE is ignored by the shell, could be fixed by trap - PIPE in the script)
  5. find … -exec … {} + (Not supported on OpenBSD)
  6. grep -F (use fgrep instead)
  7. /bin/{true,false} (use true/false instead; MacOS X)
  8. using a shell script as a command for darcs to execute (e.g. as an editor): it doesn’t work on Windows. Try a short haskell program instead, see e.g.

If in doubt, look it up at, but be aware that not all systems are conforming to the latest SUS.

How to run tests

Run just the unit tests

To build the unit tests, pass the “-ftest” flag to “cabal configure” and then do “cabal build”. To run them, do “dist/build/darcs-test/darcs-test –shell=no”. They take a while. Output like “[OK]” and “[OK, passed 100 tests]” is good. Output like “Arguments exhausted after 33 tests” is a shortage of QuickCheck test cases, not a test failure.

Run just the shell tests

You can just the shell tests like this:

dist/build/darcs-test/darcs-test --unit=no

If you have multiple cores on your machine, set the -j flag to your number of cores to speed it up:

dist/build/darcs-test/darcs-test --unit=no -j 2

If you just want to run one test through the harness, there’s a --tests flag for that (also available as -t):

dist/build/darcs-test/darcs-test --tests

Running the failing tests and network tests

Darcs also includes some tests which aren’t run by default. Some known-failing tests may be present because developers have included failing tests in advance of a fix being prepared. These tests are named tests/failing-*. To run those:

dist/build/darcs-test/darcs-test --failing=yes

Darcs does not also run tests that use that network by default, since the network may be unavailable or unreliable. To turn the network tests:

dist/build/darcs-test/darcs-test --network=yes

Tips for writing and (and reading) tests

  • Simply call darcs using “darcs” as you would in the shell. It is the responsibility of the test harness to ensure that the darcs we are testing is first in the path.

  • Always use Bash explicitly - this improves the portability of our tests.

  • There is a utility script intended for factoring out common calls and functions, called ‘lib’. It can be invoked by adding a line like ’. lib’ to your shell script. lib provides ‘set -ev’, a common definition of ‘not’, and ‘abort_windows’ for use in scripts which shouldn’t run under Windows. You don’t have to use lib if you don’t want to, or if it causes problems.

  • If you don’t use ‘lib’, always add this near the top of the script: set -ev The “v” causes the contents of the script to be printed as part of the run, which is helpful for debugging. The “e” causes the script to exit as soon as there is an error.

  • Try to avoid defining functions where possible. This makes them harder to run and generally harder to use. There are certainly cases where it is appropriate to define a function, but please do not do this just to avoid a little duplication.

  • Also try to be careful using certain utilities; ‘yes’ is prohibited since it can cause infinite loops on Mac OS X; ‘find’ can be very useful, but options and behavior can differ from GNU find to the BSD finds to Solaris’s find and so on. In general, stick to POSIX flags and functionality.

  • If you need to skip a test for any reason, the darcs-specific convention is to “exit 200”. This alerts the shell harness that the test was explicitly skipped and not passed.

  • You can use the trap feature from bash to make ensure that darcs executes some command even if the test fails. Trapping ERR lets you have your last word just before a test fails. Trapping EXIT lets you do the same before any sort of explicit exit (such as the explicit ‘exit 1’ in the ‘not’ helper function). For more details, see the bash man page or just grep trap in the test suite.

  • By default shell tests are ran only with darcs-2 patch semantics, and with the patience diff algorithm. To have a shell test running with different settings, use the pragma notation:

    #pragma repo-format darcs-2, darcs-1
    #pragma diff-algorithm patience, myers