475d8721a5
This patch introduces a new way to do functional testing on Scylla,
similar to Alternator's test/alternator but for the CQL API:
The new tests, in test/cql-pytest, are written in Python (using the pytest
framework), and use the standard Python CQL driver to connect to any CQL
implementation - be it Scylla, Cassandra, Amazon Keyspaces, or whatever.
The use of standard CQL allows the test developer to easily run the same
test against both Scylla and Cassandra, to confirm that the behaviour that
our test expects from Scylla is really the "correct" (meaning Cassandra-
compatible) behavior.
A developer can run Scylla or Cassandra manually, and run "pytest"
to connect to them (see README.md for more instructions). But even more
usefully, this patch also provides two scripts: test/cql-pytest/run and
test/cql-pytest/run-cassandra. These scripts automate the task of running
Scylla or Cassandra (respectively) in a random IP address and temporary
directory, and running the tests against it.
The script test/cql-pytest/run is inspired by the existing test run
scripts of Alternator and Redis, but rewritten in Python in a way that
will make it easy to rewrite - in a future patch - all these other run
scripts to use the same common code to safely run a test server in a
temporary directory.
"run" is extremely quick, taking around two seconds to boot Scylla.
"run-cassandra" is slower, taking 13 seconds to boot Cassandra (maybe
this can be improved in the future, I still don't know how).
The tests themselves take milliseconds.
Although the 'run' script runs a single Scylla node, the developer
can also bring up any size of Scylla or Cassandra cluster manually
and run the tests (with "pytest") against this cluster.
This new test framework differs from the existing alternatives in the
following ways:
dtest: dtest focuses on testing correctness of *distributed* behavior,
involving clusters of multiple nodes and often cluster changes
during the test. In contrast, cql-pytest focuses on testing the
*functionality* of a large number of small CQL features - which
can usually be tested on a single-node cluster.
Additionally, dtest is out-of-tree, while cql-pytest is in-tree,
making it much easier to add or change tests together with code
patches.
Finally, dtest tests are notoriously slow. Hundreds of tests in
the new framework can finish faster than a single dtest.
Slow and out-of-tree tests are difficult to write, and I believe
this explains why no developer loves writing dtests and maintainers
do not insist on having them. I hope cql-pytest can change that.
test/cql: The defining difference between the existing test/cql suite
and the new test/cql-pytest is the new framework is programmatic,
Python code, not a text file with desired output. Tests written with
` code allow things like looping, repeating the same test with different
parameters. Also, when a test fails, it makes it easier to understand
why it failed beyond just the fact that the output changed.
Moreover, in some cases, the output changes benignly and cql-pytest
may check just the desired features of the output.
Beyond this, the current version of test/cql cannot run against
Cassandra. test/cql-pytest can.
The primary motivation for this new framework was
https://github.com/scylladb/scylla/issues/7443 - where we had an
esoteric feature (sort order of *partitions* when an index is addded),
which can be shown in Cqlsh to have what we think is incorrect behavior,
and yet: 1. We didn't catch this bug because we never wrote a test for it,
possibly because it too difficult to contribute tests, and 2. We *thought*
that we knew what Cassandra does in this case, but nobody actually tested
it. Yes, we can test it manually with cqlsh, but wouldn't everything be
better if we could just run the same test that we wrote for Scylla against
Cassandra?
So one of the tests we add in this patch confirms issue #7443 in Scylla,
and that our hunch was correct and Cassandra indeed does not have this
problem. I also add a few trivial tests for keyspace create and drop,
as additional simple examples.
Refs #7443.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20201110110301.672148-1-nyh@scylladb.com>
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Single-node funtional tests for Scylla's CQL features. Tests use the Python CQL library and the pytest frameworks. By using an actual CQL library for the tests, they can be run against any implementation of CQL - both Scylla and Cassandra. Most tests - except in rare cases - should pass on both, to ensure that Scylla is compatible with Cassandra in most features.
To run all tests against an already-running local installation of Scylla
or Cassandra on localhost, just run pytest. The "--host" and "--port"
can be used to give a different location for the running Scylla or Cassanra.
More conveniently, we have two scripts - "run" and "run-cassandra" - which do all the work necessary to start Scylla or Cassandra (respectively), and run the tests on them. The Scylla or Cassandra process is run in a temporary directory which is automatically deleted when the test ends.
Additional options can be passed to "pytest" or to "run" / "run-cassandra" to control which tests to run:
- To run all tests in a single file, do
pytest test_table.py. - To run a single specific test, do
pytest test_table.py::test_create_table_unsupported_names.
Additional useful pytest options, especially useful for debugging tests:
- -v: show the names of each individual test running instead of just dots.
- -s: show the full output of running tests (by default, pytest captures the test's output and only displays it if a test fails)