Fake implementation of redis API for testing purposes.
Project description
fakeredis: A fake version of a redis-py
Intro | How to Use | Contributing | Guides | Sponsoring
Intro
fakeredis is a pure-Python implementation of the redis-py python client that simulates talking to a redis server. This was created for a single purpose: to write tests. Setting up redis is not hard, but many times you want to write tests that do not talk to an external server (such as redis). This module now allows tests to simply use this module as a reasonable substitute for redis.
For a list of supported/unsupported redis commands, see REDIS_COMMANDS.md.
Installation
To install fakeredis-py, simply:
$ pip install fakeredis
You will need lupa if you want to run Lua scripts
(this includes features like redis.lock.Lock, which are implemented in Lua).
If you install fakeredis with pip install fakeredis[lua] it will be automatically installed.
How to Use
FakeRedis can imitate Redis server version 6.x or 7.x. If you do not specify the version, version 7 is used by default.
The intent is for fakeredis to act as though you're talking to a real redis server. It does this by storing state internally. For example:
>>> import fakeredis
>>> r = fakeredis.FakeStrictRedis(version=6)
>>> r.set('foo', 'bar')
True
>>> r.get('foo')
'bar'
>>> r.lpush('bar', 1)
1
>>> r.lpush('bar', 2)
2
>>> r.lrange('bar', 0, -1)
[2, 1]
The state is stored in an instance of FakeServer. If one is not provided at
construction, a new instance is automatically created for you, but you can
explicitly create one to share state:
>>> import fakeredis
>>> server = fakeredis.FakeServer()
>>> r1 = fakeredis.FakeStrictRedis(server=server)
>>> r1.set('foo', 'bar')
True
>>> r2 = fakeredis.FakeStrictRedis(server=server)
>>> r2.get('foo')
'bar'
>>> r2.set('bar', 'baz')
True
>>> r1.get('bar')
'baz'
>>> r2.get('bar')
'baz'
It is also possible to mock connection errors, so you can effectively test
your error handling. Simply set the connected attribute of the server to
False after initialization.
>>> import fakeredis
>>> server = fakeredis.FakeServer()
>>> server.connected = False
>>> r = fakeredis.FakeStrictRedis(server=server)
>>> r.set('foo', 'bar')
ConnectionError: FakeRedis is emulating a connection error.
>>> server.connected = True
>>> r.set('foo', 'bar')
True
Fakeredis implements the same interface as redis-py, the popular
redis client for python, and models the responses of redis 6.x or 7.x.
Use to test django-rq
There is a need to override django_rq.queues.get_redis_connection with
a method returning the same connection.
from fakeredis import FakeRedisConnSingleton
django_rq.queues.get_redis_connection = FakeRedisConnSingleton()
Limitations
Apart from unimplemented commands, there are a number of cases where fakeredis won't give identical results to real redis. The following are differences that are unlikely to ever be fixed; there are also differences that are fixable (such as commands that do not support all features) which should be filed as bugs in GitHub.
-
Hyperloglogs are implemented using sets underneath. This means that the
typecommand will return the wrong answer, you can't usegetto retrieve the encoded value, and counts will be slightly different (they will in fact be exact). -
When a command has multiple error conditions, such as operating on a key of the wrong type and an integer argument is not well-formed, the choice of error to return may not match redis.
-
The
incrbyfloatandhincrbyfloatcommands in redis use the Clong doubletype, which typically has more precision than Python'sfloattype. -
Redis makes guarantees about the order in which clients blocked on blocking commands are woken up. Fakeredis does not honour these guarantees.
-
Where redis contains bugs, fakeredis generally does not try to provide exact bug-compatibility. It's not practical for fakeredis to try to match the set of bugs in your specific version of redis.
-
There are a number of cases where the behaviour of redis is undefined, such as the order of elements returned by set and hash commands. Fakeredis will generally not produce the same results, and in Python versions before 3.6 may produce different results each time the process is re-run.
-
SCAN/ZSCAN/HSCAN/SSCAN will not necessarily iterate all items if items are deleted or renamed during iteration. They also won't necessarily iterate in the same chunk sizes or the same order as redis.
-
DUMP/RESTORE will not return or expect data in the RDB format. Instead, the
picklemodule is used to mimic an opaque and non-standard format. WARNING: Do not use RESTORE with untrusted data, as a malicious pickle can execute arbitrary code.
Local development environment
To ensure parity with the real redis, there are a set of integration tests that mirror the unittests. For every unittest that is written, the same test is run against a real redis instance using a real redis-py client instance. In order to run these tests you must have a redis server running on localhost, port 6379 (the default settings). WARNING: the tests will completely wipe your database!
First install poetry if you don't have it, and then install all the dependencies:
pip install poetry
poetry install
To run all the tests:
poetry run pytest -v
If you only want to run tests against fake redis, without a real redis::
poetry run pytest -m fake
Because this module is attempting to provide the same interface as redis-py,
the python bindings to redis, a reasonable way to test this to take each
unittest and run it against a real redis server. fakeredis and the real redis
server should give the same result. To run tests against a real redis instance
instead:
poetry run pytest -m real
If redis is not running, and you try to run tests against a real redis server, these tests will have a result of 's' for skipped.
There are some tests that test redis blocking operations that are somewhat slow. If you want to skip these tests during day to day development, they have all been tagged as 'slow' so you can skip them by running:
poetry run pytest -m "not slow"
Contributing
Contributions are welcome. Please see the contributing guide for more details.
If you'd like to help out, you can start with any of the issues labeled with Help wanted.
Guides
Implementing support for a command
Creating a new command support should be done in the FakeSocket class (in _fakesocket.py) by creating the method
and using @command decorator (which should be the command syntax, you can use existing samples on the file).
For example:
class FakeSocket(BaseFakeSocket, FakeLuaSocket):
# ...
@command(...)
def zscore(self, key, member):
try:
return self._encodefloat(key.value[member], False)
except KeyError:
return None
Implement a test for it
There are multiple scenarios for test, with different versions of redis server, redis-py, etc. The tests not only assert the validity of output but runs the same test on a real redis-server and compares the output to the real server output.
- Create tests in the
test_fakeredis6.pyif the command is supported in redis server 6.x. - Alternatively, create the test in
test_fakeredis7.pyif the command is supported only on redis server 7.x. - If support for the command was introduced in a certain version of redis-py (
see redis-py release notes) you can use the
decorator
@testtools.run_test_if_redispy_veron your tests. example:
@testtools.run_test_if_redispy_ver('above', '4.2.0') # This will run for redis-py 4.2.0 or above.
def test_expire_should_not_expire__when_no_expire_is_set(r):
r.set('foo', 'bar')
assert r.get('foo') == b'bar'
assert r.expire('foo', 1, xx=True) == 0
Updating REDIS_COMMANDS.md
Lastly, run from the root of the project the script to regenerate REDIS_COMMANDS.md:
python scripts/supported.py > REDIS_COMMANDS.md
Sponsor
fakeredis-py is developed for free.
You can support this project by becoming a sponsor using this link.
Alternatively, you can buy me coffee using this
link:
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