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Testing

Introduction

test.py is a regression testing harness shipped along with scylla.git, which runs C++, unit, CQL and python tests.

This is a manual for test.py.

Installation

To run test.py, Python 3.7 or higher is required. ./install-dependencies.sh should install all the required Python modules. If install-dependencies.sh does not support your distribution, please manually install all Python modules it lists with pip.

Additionally, toolchain/dbuid could be used to run test.py. In this case you don't need to run ./install-dependencies.sh

Usage

In order to invoke test.py, you need to build first. ./test.py will run all existing tests in all configured build modes:

$ ./test.py

In order to invoke test.py with toolchain/dbuild, you need to run

$ ./tools/toolchain/dbuild ./test.py

If you want to specify a specific build mode:

$ ./test.py --mode=dev

If you want to run only a specific test:

$ ./test.py suitename/testname

This will select and run all tests having suitename/testname as substring, e.g. suitename/testname_ext and others.

If you want to run only a specific test-case from a specific test:

$ ./test.py suitename/testname::casename

This will select only the test with the suitename/testname name, no substring search is performed in this case. If the casename is *, then all test-cases will be selected.

Note that not all tests are divided into cases. Below sections will shed more light on this.

Build artefacts, such as test output and harness output is stored in ./testlog. Scylla data files are stored in /tmp.

How it works

On start, test.py invokes ninja to find out configured build modes. Then it searches all subdirectories of ./test/ for suite.yaml files: each directory containing suite.yaml is a test suite, in which test.py then looks for tests. All files ending with _test.cc or _test.cql are considered tests.

A suite must contain tests of the same type, as configured in suite.yaml. The list of found tests is matched with the optional command line test name filter. A match is registered if filter substring exists anywhere in test full name. For example:

$ ./test.py cql

runs cql/lwt_test, cql/lwt_batch_test, as well as boost/cql_query_test.

The ./testlog directory is created if it doesn't exist, otherwise it is cleared from the previous run artefacts.

Matched tests are run concurrently, with concurrency factor set to the number of available CPU cores. test.py continues until all tests are run even if any one of them fails.

CQL tests

The main idea of CQL tests is that test writer specifies CQL statements run against Scylla, and (almost) everything else is done by test.py: statement output is recorded in a dedicated file, and later used to validate correctness of the test. The initial validation must be of course performed by the author of the test. This approach is sometimes called "approval testing" and discussion about pros and cons of this methodology is widely available online.

To run CQL tests, test.py uses an auxiliary program, test/pylib/cql_repl/cql_repl.py. This program reads CQL input file, evaluates it against a pre-started Scylla using CQL database connection, and prints output in tabular format to stdout. A default keyspace is created automatically.

test.py invokes cql_repl.py as a pytest providing the test file and redirecting its output to a temporary file in testlog directory.

After cql_repl.py finishes, test.py compares the output stored in the temporary file with a pre-recorded output stored in test/suitename/testname_test.result.

The test is considered failed if executing any CQL statement produced an error (e.g. because the server crashed during execution) or server output does not match one recorded in testname.result, or there is no testname.result. The latter is possible when it's the first invocation of the test ever.

In the event of output mismatch file test/suitename/testname_test.reject is created, and first lines of the diff between the two files are output. To update .result file with new output, simply overwrite it with the reject file:

mv test/suitename/testname.re*

Note Since the result file is effectively part of the test, developers must thoroughly examine the diff and understand the reasons for every change before overwriting .result files.

Debugging CQL tests

To debug CQL tests, one can run CQL against a standalone Scylla (possibly started in debugger) using cqlsh.

Unit tests

The same unit test can be run in different seastar configurations, i.e. with different command line arguments. The custom arguments can be set in custom_args key of the suite.yaml file.

Tests from boost suite are divided into test-cases. These are top-level functions wrapped by BOOST_AUTO_TEST_CASE, SEASTAR_TEST_CASE or alike. Boost tests support suitename/testname::casename selection described above.

Debugging unit tests

If a test fails, its log can be found in testlog/${mode}/testname.log. By default, all unit tests are built stripped. To build non-stripped tests, ./configure with --tests-debuginfo list-of-tests. test.py adds some command line arguments to unit tests. The exact way in which the test is invoked is recorded in testlog/test.py.log.

Python tests

test.py supports pytest standard of tests, for suites (directories) specifying Python test type in their suite.yaml. For such tests, a standalone server instance is created, and a connection URI to the server is passed to the test. Thanks to convenience fixtures, test writers don't need to create or cleanup connections or keyspaces. test.py will also keep track of the used server(s) and will shut down the server when all tests using it end.

Note that some suites have a convenience helper script called run. Find more information about it in test/cql-pytest and test/alternator.

All tests in pytest suites consist of test-cases -- top-level functions starting with test_ -- and thus support the suitename/testname::casename selection described above.

Sharing and pooling servers

Since there can be many pytests in a single directory (e.g. cql-pytest) test.py creates multiple servers to parallelize their execution. Each server is also shared among many tests, to save on setup/teardown steps. While this speeds up execution, sharing servers complicates debugging if a test fails.

Specifically, you should avoid leaving global artifacts in your test, even if it fails. Typically, you could use a built-in keyspace() fixture to create a randomly named keyspace.

At start and end of each test, test.py performs a number of sanity checks of the used server:

  • it should be up and running,
  • it should not contain non-system keyspaces.

Debugging a pytest.

To have a full picture for a failing pytest it is necessary to identify the server which was used to run it and the relevant fragment in the server log. For this, test.py maintains this link through relevant log messages and preserves Scylla output on test failure.

A typical debugging journey should start with looking at test.py.log in testlog where, for each test it runs, test.py prints all relevant paths to server log and pytest output.

To extend test.py logging, you can use the standard 'logging' module API. Individual pytests are programmed to not gobble stdout, so you can can also add prints to pytests, and they will end up in the test' log.

For example, imagine cql-pytest/test_null.py fails. The relevant lines in test.py.log will be:

21:53:04.789 INFO> Created cluster {127.101.161.1}
21:53:04.790 INFO> Leasing Scylla cluster {127.101.161.1} for test test_null.1
21:53:04.790 INFO> Starting test test_null.1: pytest --host=127.101.161.1 -s ...test/cql-pytest/test_null.py
21:53:05.533 INFO> Test test_null.1 failed

To find out the working directory of instance 127.101.161.1 search for its initialization message in test.py.log:

10:05:51.722 INFO> installing Scylla server in /opt/local/work/scylla/scylla/testlog/dev/scylla-1...
10:05:51.722 INFO> starting server at host 127.159.235.1 in scylla-1...
10:05:52.688 INFO> started server at host 127.159.235.1 in scylla-1, pid 2165602

Next, we can take a look at the server log, which is at /opt/local/work/scylla/scylla/testlog/dev/scylla-1.log:

The log contains special markers, written at test start and end:

INFO  2022-08-18 10:05:52,598 [shard 0] schema_tables - Schema version changed to 8b5e9c73-7c1c-3b28-8c31-c1359210c484
------ Starting test test_null.1 ------
...
INFO  2022-08-18 10:05:53,297 [shard 0] schema_tables - Dropping keyspace cql_test_1660806353124
INFO  2022-08-18 10:05:53,304 [shard 0] schema_tables - Schema version changed to 8b5e9c73-7c1c-3b28-8c31-c1359210c484
------ Ending test test_null.1 ------

Most often there are no errors in Scylla log, so next we inspect the test' log, which is next to the server's at /opt/local/scylla/scylla/testlog/dev/test_null.1.log:

        cql.execute(f"INSERT INTO {table1} (p,c) VALUES ('{p}', '3')")
>       assert False
E       assert False

What does number 1 mean in the log file name? Since test.py can run parallel jobs and run each test multiple times with --repeat, each execution is assigned a unique sequence number, allowing to distinguish artifacts of different execution.

When finished debugging, you don't have to worry about deleting the remains of a previous run, test.py will clean then up on the next execution automatically.

Pooling implementation details

When pooling and running multiple servers, we want to avoid host/port or temporary directory clashes. We also want to make sure that test.py doesn't leave any running servers around, even when it's interrupted by user or with an exception. This is why test.py has a special registry where it tracks all servers, in which each server gets a unique address in a subnet of network 127.*.*.*. Unless killed with SIGKILL, test.py kills all servers it creates at shutdown.

The servers created by the pool use a pre-defined set of options to speed up boot. Some of these options are developer-only, such as flush_schema_tables_after_modification: false. If you wish to extend the options of a used server, you can do it by adding extra_scylla_cmdline_options or extra_scylla_config_options to your suite.yaml.

Topology pytests

In addition to the standard 'Python' suite type, test.py supports an extended pytest suite, Topology. Unlike Python tests, Topology tests run against Scylla clusters, and support topology operations. A standard manager fixture is available for these. Through this fixture, you can access individual nodes, start, stop and restart instances, add and remove instances from the cluster. The manager fixture connects to the cluster by sending test.py HTTP/REST commands over a unix-domain socket. This guarantees that test.py is fully aware of all topology operations and can clean up resources, including added servers, when tests end. test.py automatically detects if a cluster can not be shared with a subsequent test because it was manipulated with. Today the check is quite simple: any cluster that has has nodes added or removed, started or stopped, even if it ended up in the same state as it was at the beginning of the test, is considered "dirty". Such clusters are not returned to the pool, but destroyed, and the pool is replenished with a new cluster instead.

Automation, CI, and Jenkins

If any of the tests fails, test.py returns a non-zero exit status. JUNIT and XUNIT execution status XML files can be found in testlog/${mode}/xml/ directory. These files are used by Jenkins to produce formatted build reports. test.py will try to add as much context information, such as fragments of log files, exceptions, to the test XML output.

If that's not enough, a debugging journey, similar to a local one, is available in CI if you navigate to 'Build artifacts' at the Jenkins build page. This will bring you to a folder with all the test logs, preserved by Jenkins in event of test failure.

Stability

Testing is hard. Testing ScyllaDB is even harder, but we strive to ensure our testing suite is as solid as possible. The first step is contributing a stable (read: non-flaky) test. To do so, when developing tests, please run them (1) in debug mode and (2) 100 times in a row (using --repeat 100), and see that they pass successfully.

Allure reporting

To make analyzing of the test results more convenient, an allure reporting tool is introduced. Python module allure-pytest is included in the toolchain image and an additional parameter added to gather allure data for the test run. However, the allure binary is not a part of the toolchain image. So to have the full benefit of the new reporting tool allure binary should be installed locally.

Allure installation

To install allure tool, please follow official documentation

Note: rpm package requires dependency default-jre-headless but on Fedora 38,39 none of the packages provides it. So manual installation of allure is required.

Basic allure usage

  1. Open directory with the Junit xml test results, e.g. testlog/dev/xml
  2. Execute allure serve to show report
$ allure serve -h localhost .

This will open the default system browser with an interactive allure report.

For more information please refer to allure -h or official documentation

See also

For command line help and available options, please see also:

    $ ./test.py --help