pytest-subprocess
Pytest plugin to fake subprocess.
Usage
The plugin adds the fake_process fixture (and fp as an alias).
It can be used it to register subprocess results so you won't need to rely on
the real processes. The plugin hooks on the subprocess.Popen(), which is
the base for other subprocess functions. That makes the subprocess.run(),
subprocess.call(), subprocess.check_call() and
subprocess.check_output() methods also functional.
Installation
You can install pytest-subprocess via pip from PyPI:
$ pip install pytest-subprocess
Basic usage
The most important method is fp.register()
(or register_subprocess if you prefer to be more verbose), which
allows defining the fake processes behavior.
def test_echo_null_byte(fp):
fp.register(["echo", "-ne", "\x00"], stdout=bytes.fromhex("00"))
process = subprocess.Popen(
["echo", "-ne", "\x00"],
stdout=subprocess.PIPE,
)
out, _ = process.communicate()
assert process.returncode == 0
assert out == b"\x00"Optionally, the stdout and stderr parameters can be a list (or tuple)
of lines to be joined together with a trailing os.linesep on each line.
def test_git(fp):
fp.register(["git", "branch"], stdout=["* fake_branch", " master"])
process = subprocess.Popen(
["git", "branch"],
stdout=subprocess.PIPE,
universal_newlines=True,
)
out, _ = process.communicate()
assert process.returncode == 0
assert out == "* fake_branch\n master\n"Passing input
By default, if you use input argument to the Popen.communicate()
method, it won't crash, but also won't do anything useful. By passing
a function as stdin_callable argument for the
fp.register() method you can specify the behavior
based on the input. The function shall accept one argument, which will be
the input data. If the function will return a dictionary with stdout or
stderr keys, its value will be appended to according stream.
def test_pass_input(fp):
def stdin_function(input):
return {
"stdout": "This input was added: {data}".format(
data=input.decode()
)
}
fp.register(
["command"],
stdout=[b"Just stdout"],
stdin_callable=stdin_function,
)
process = subprocess.Popen(
["command"],
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
)
out, _ = process.communicate(input=b"sample input\n")
assert out.splitlines() == [
b"Just stdout",
b"This input was added: sample input",
]Unregistered commands
By default, when the fp fixture is being used, any attempt to
run subprocess that has not been registered will raise
the ProcessNotRegisteredError exception. To allow it, use
fp.allow_unregistered(True), which will execute all unregistered
processes with real subprocess, or use
fp.pass_command("command") to allow just a single command.
def test_real_process(fp):
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
# this will fail, as "ls" command is not registered
subprocess.call("ls")
fp.pass_command("ls")
# now it should be fine
assert subprocess.call("ls") == 0
# allow all commands to be called by real subprocess
fp.allow_unregistered(True)
assert subprocess.call(["ls", "-l"]) == 0Differing results
Each register() or pass_command() method call will register
only one command execution. You can call those methods multiple times, to
change the faked output on each subprocess run. When you call subprocess more
will be raised. To prevent that, call fp.keep_last_process(True),
which will keep the last registered process forever.
def test_different_output(fp):
# register process with output changing each execution
fp.register("test", stdout="first execution")
# the second execution will return non-zero exit code
fp.register("test", stdout="second execution", returncode=1)
assert subprocess.check_output("test") == b"first execution"
second_process = subprocess.run("test", stdout=subprocess.PIPE)
assert second_process.stdout == b"second execution"
assert second_process.returncode == 1
# 3rd time shall raise an exception
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
subprocess.check_call("test")
# now, register two processes once again,
# but the last one will be kept forever
fp.register("test", stdout="first execution")
fp.register("test", stdout="second execution")
fp.keep_last_process(True)
# now the processes can be called forever
assert subprocess.check_output("test") == b"first execution"
assert subprocess.check_output("test") == b"second execution"
assert subprocess.check_output("test") == b"second execution"
assert subprocess.check_output("test") == b"second execution"Using callbacks
You can pass a function as callback argument to the register()
method which will be executed instead of the real subprocess. The callback function
can raise exceptions which will be interpreted in tests as an exception raised
by the subprocess. The fixture will pass FakePopen class instance into the
callback function, that can be used to change the return code or modify output
streams.
def callback_function(process):
process.returncode = 1
raise PermissionError("exception raised by subprocess")
def test_raise_exception(fp):
fp.register(["test"], callback=callback_function)
with pytest.raises(
PermissionError, match="exception raised by subprocess"
):
process = subprocess.Popen(["test"])
process.wait()
assert process.returncode == 1It is possible to pass additional keyword arguments into callback by using
the callback_kwargs argument:
def callback_function_with_kwargs(process, return_code):
process.returncode = return_code
def test_callback_with_arguments(fp):
return_code = 127
fp.register(
["test"],
callback=callback_function_with_kwargs,
callback_kwargs={"return_code": return_code},
)
process = subprocess.Popen(["test"])
process.wait()
assert process.returncode == return_codeAs a context manager
The fp fixture provides context() method that allows us to
use it as a context manager. It can be used to limit the scope when a certain
command is allowed, e.g. to make sure that the code doesn't want to execute
it somewhere else.
def test_context_manager(fp):
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
# command not registered, so will raise an exception
subprocess.check_call("test")
with fp.context() as nested_process:
nested_process.register("test", occurrences=3)
# now, we can call the command 3 times without error
assert subprocess.check_call("test") == 0
assert subprocess.check_call("test") == 0
# the command was called 2 times, so one occurrence left, but since the
# context manager has been left, it is not registered anymore
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
subprocess.check_call("test")Non-exact command matching
If you need to catch a command with some non-predictable elements, like a path
to a randomly-generated file name, you can use fake_subprocess.any() for
that purpose. The number of arguments that should be matched can be controlled
by min and max arguments. To use fake_subprocess.any() you need
to define the command as a tuple or list. The matching will work even
if the subprocess command will be called with a string argument.
def test_non_exact_matching(fp):
# define a command that will take any number of arguments
fp.register(["ls", fp.any()])
assert subprocess.check_call("ls -lah") == 0
# `fake_subprocess.any()` is OK even with no arguments
fp.register(["ls", fp.any()])
assert subprocess.check_call("ls") == 0
# but it can force a minimum amount of arguments
fp.register(["cp", fp.any(min=2)])
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
# only one argument is used, so registered command won't match
subprocess.check_call("cp /source/dir")
# but two arguments will be fine
assert subprocess.check_call("cp /source/dir /tmp/random-dir") == 0
# the `max` argument can be used to limit maximum amount of arguments
fp.register(["cd", fp.any(max=1)])
with pytest.raises(fp.exceptions.ProcessNotRegisteredError):
# cd with two arguments won't match with max=1
subprocess.check_call("cd ~/ /tmp")
# but any single argument is fine
assert subprocess.check_call("cd ~/") == 0
# `min` and `max` can be used together
fp.register(["my_app", fp.any(min=1, max=2)])
assert subprocess.check_call(["my_app", "--help"]) == 0Check if process was called
You may want to simply check if a certain command was called, you can do this
by accessing fp.calls, where all commands are stored as-called.
You can also use a utility function fp.call_count() to see
how many a command has been called. The latter supports fp.any().
def test_check_if_called(fp):
fp.keep_last_process(True)
# any command can be called
fp.register([fp.any()])
subprocess.check_call(["cp", "/tmp/source", "/source"])
subprocess.check_call(["cp", "/source", "/destination"])
subprocess.check_call(["cp", "/source", "/other/destination"])
# you can check if command is in ``fp.calls``
assert ["cp", "/tmp/source", "/source"] in fp.calls
assert ["cp", "/source", "/destination"] in fp.calls
assert ["cp", "/source", "/other/destination"] in fp.calls
# or check how many it was called, possibly with wildcard arguments
assert fp.call_count(["cp", "/source", "/destination"]) == 1
# with ``call_count()`` you don't need to use the same type as
# the subprocess was called
assert fp.call_count("cp /tmp/source /source") == 1
# can be used with ``fp.any()`` to match more calls
assert fp.call_count(["cp", fp.any()]) == 3Handling signals
You can use standard kill(), terminate() or send_signal() methods
in Popen instances. There is an additional received_signals() method
to get a tuple of all signals received by the process. It is also possible to
set up an optional callback function for signals.
import signal
def test_signal_callback(fp):
"""Test that signal callbacks work."""
def callback(process, sig):
if sig == signal.SIGTERM:
process.returncode = -1
# the `register()` method returns a ProgressRecorder object, where
# all future matching `Popen()` instances will be appended
process_recorder = fp.register("test", signal_callback=callback)
process = subprocess.Popen("test")
process.send_signal(signal.SIGTERM)
process.wait()
assert process.returncode == -1
assert process.received_signals() == (signal.SIGTERM,)
# the instance appended to `register()` output is the `Popen` instance
# created later
assert process_recorder.first_call is processAsyncio support
The plugin now supports asyncio and works for asyncio.create_subprocess_shell
and asyncio.create_subprocess_exec:
@pytest.mark.asyncio
async def test_basic_usage(
fp,
):
fp.register(
["some-command-that-is-definitely-unavailable"], returncode=500
)
process = await asyncio.create_subprocess_shell(
"some-command-that-is-definitely-unavailable"
)
returncode = await process.wait()
assert process.returncode == returncode
assert process.returncode == 500Documentation
For full documentation, including API reference, please see https://pytest-subprocess.readthedocs.io/en/latest/.
Contributing
Contributions are very welcome. Tests can be run with tox, please ensure the coverage at least stays the same before you submit a pull request.
License
Distributed under the terms of the MIT license, "pytest-subprocess" is free and open source software
Issues
If you encounter any problems, please file an issue along with a detailed description.
This pytest plugin was generated with Cookiecutter along with @hackebrot's cookiecutter-pytest-plugin template.