How our testing works

We use the test tooling of postgres to run our tests. This tooling is very simple but effective. The basics it runs a series of .sql scripts, gets their output and stores that in results/$sqlfilename.out. It then compares the actual output to the expected output with a simple diff command:

diff results/$sqlfilename.out expected/$sqlfilename.out


Which sql scripts to run is defined in a schedule file, e.g. multi_schedule, multi_mx_schedule.


In our Makefile we have rules to run the different types of test schedules. You can run them from the root of the repository like so:

# e.g. the multi_schedule
make install -j9 && make -C src/test/regress/ check-multi

Take a look at the makefile for a list of all the testing targets.

Running a specific test

Often you want to run a specific test and don’t want to run everything. You can simply use [test_name] script like below in that case. It detects the test schedule and make target to run the given test.

src/test/regress/citus_tests/ multi_utility_warnings

You can pass --repeat or r parameter to run the given test for multiple times.

src/test/regress/citus_tests/ multi_utility_warnings -r 1000

To force the script to use base schedules rather than minimal ones, you can pass -b or --use-base-schedule.

src/test/regress/citus_tests/ coordinator_shouldhaveshards -r 1000 --use-base-schedule

If you would like to run a specific test on a certain target you can use one of the following commands to do so:

# If your tests needs almost no setup you can use check-minimal
make install -j9 && make -C src/test/regress/ check-minimal EXTRA_TESTS='multi_utility_warnings'
# Often tests need some testing data, if you get missing table errors using
# check-minimal you should try check-base
make install -j9 && make -C src/test/regress/ check-base EXTRA_TESTS='with_prepare'
# Sometimes this is still not enough and some other test needs to be run before
# the test you want to run. You can do so by adding it to EXTRA_TESTS too.
make install -j9 && make -C src/test/regress/ check-base EXTRA_TESTS='add_coordinator coordinator_shouldhaveshards'


The output of tests is sadly not completely predictable. Still we want to compare the output of different runs and error when the important things are different. We do this by not using the regular system diff to compare files. Instead we use src/test/regress/bin/diff which does the following things:

  1. Change the $sqlfilename.out file by running it through sed using the src/test/regress/bin/normalize.sed file. This does stuff like replacing numbers that keep changing across runs with an XXX string, e.g. portnumbers or transaction numbers.
  2. Backup the original output to $sqlfilename.out.unmodified in case it’s needed for debugging
  3. Compare the changed results and expected files with the system diff command.

Updating the expected test output

Sometimes you add a test to an existing file, or test output changes in a way that’s not bad (possibly even good if support for queries is added). In those cases you want to update the expected test output. The way to do this is very simple, you run the test and copy the new .out file in the results directory to the expected directory, e.g.:

make install -j9 && make -C src/test/regress/ check-minimal EXTRA_TESTS='multi_utility_warnings'
cp src/test/regress/{results,expected}/multi_utility_warnings.out

Adding a new test file

Adding a new test file is quite simple:

  1. Write the SQL file in the sql directory
  2. Add it to a schedule file, to make sure it’s run in CI
  3. Run the test
  4. Check that the output is as expected
  5. Copy the .out file from results to expected

Isolation testing

See src/test/regress/spec/

Pytest testing

See src/test/regress/citus_tests/test/

Upgrade testing

See src/test/regress/citus_tests/upgrade/

Arbitrary configs testing

See src/test/regress/citus_tests/arbitrary_configs/

Failure testing

See src/test/regress/mitmscripts/

Perl test setup script

To automatically setup a citus cluster in tests we use our src/test/regress/ script. This sets up a citus cluster and then starts the standard postgres test tooling. You almost never have to change this file.

Handling different test outputs

Sometimes the test output changes because we run tests in different configurations. The most common example is an output that changes in different Postgres versions. We highly encourage to find a way to avoid these test outputs. You can try the following, if applicable to the changing output:

  • Change the test such that you still test what you want, but you avoid the different test outputs.
  • Reduce the test verbosity via: \set VERBOSITY terse, SET client_min_messages TO error, etc
  • Drop the specific test lines altogether, if the test is not critical.
  • Use utility functions that modify the output to your preference, like coordinator_plan, which modifies EXPLAIN output
  • Add a normalization rule

Alternative test output files are highly discouraged, so only add one when strictly necessary. In order to maintain a clean test suite, make sure to explain why it has an alternative output in the test header, and when we can drop the alternative output file in the future.

For example:

-- This test file has an alternative output because of the change in the
-- display of SQL-standard function's arguments in INSERT/SELECT in PG15.
-- The alternative output can be deleted when we drop support for PG14

Including important keywords, like “PG14”, “PG15”, “alternative output” will help cleaning up in the future.

Randomly failing tests

In CI sometimes a test fails randomly, we call these tests “flaky”. To fix these flaky tests see src/test/regress/