1. The test framework

The code base has unit and integration tests that can be executed automatically to ensure the program works as intended. Such tests are often written to trigger a bug and to ensure the bug is detected if it resurfaces in the future, but also to validate behavior of components and interfaces.

The tests are collected in the tests/ directory. The individual tests are in subdirectories of this directory. The tests are grouped in directories.

2. Running tests

The tests are executed by the scripts/runtests script generated from scripts/runtests.in during build. The runtests script will by default locate tests to run under tests/, but can be limited to only run a limited set of tests by specifying the directory of the test or tests as argument(s).

An example running only the tests in tests/lathe/.
$ scripts/runtests tests/lathe/
Running test: tests/lathe
Runtest: 1 tests run, 1 successful, 0 failed + 0 expected, 0 skipped

The runtests script looks for all files named test, test.sh or test.hal below the directories specified on the command line, or under tests/ if no command line argument is specified. These files represent three different ways to run the tests.

The runtests script accepts the following arguments, see the output from scripts/runtests -h for the authoritative list:

-n  do not remove temporary files for successful tests.
-s  stop after any failed test.
-p  print stderr and result files.
-c  Remove temporary files from an earlier test run.
-u  Only run tests that require normal user access.
-v  Show stdout and stderr (normally it's hidden).

3. Writing tests

Make sure the test can run successfully without a working X11 display, i.e. with the DISPLAY environment variable unset.

  1. Create a folder in tests/.

  2. Provide one test script.

  3. Evaluate the output with one of the options below.

These are the files considered in the directory with the individual tests:

Test script (only one of these three)

A program that is executed and its exit code and output checked using either checkresult or expected.


A bash script that is executed and its exit code and output checked using either checkresult or expected.


A HAL script that is executed using halrun -f test.hal and its exit code and output checked using either checkresult or expected.

Test evaluation

A file whose content is compared to the output from running the test scripts. If the test output is identical to the content of the expected file, the test succeeds.


An executable file to perform more complex validation than just comparing the output of a test script. It gets the filename of the test program as its command line argument. The exit code of this program controls the result of the test. If both expected and checkresult exist, only checkresult is consulted to validate the test output.


If this file exist, a test failure is expected and does not cause runtests to return an exit code signaling an error.


If this file exist, the test is skipped and not executed at all.


This file can be used to flag specific needs in the test. At the moment, the use of sudo can be flagged, and tests requiring sudo can be skipped when using runtests -u. To flag such requirements, add a line with Restrictions: sudo to this file.

4. Some testing approaches

There are various ways to structure a test, depending on what one wants to test. Here are a few ideas on how to do it.

4.1. Non-interactive "GUI"

If you want to test some operations in the user interface, a useful approach is is to write a custom "GUI" simulating the operations. This can be done by creating a normal LinuxCNC setup and pointing the [DISPLAY] DISPLAY value to a script that does the operations needed to test the behaviour.

Examples of this approach can be found in tests/halui/jogging/ and tests/interp/subroutine-return/.

4.2. Recording HAL pin transitions

Using the sampler and halsampler HAL components, one can set up a HAL configuration and collect pin value settings and changes and dump the result to stdout (or a file). The end result can then be compared with the expected output to verify if HAL behaves as expected.

Examples of this approach can be found in tests/multiclick/ and tests/stepgen.2/.