I am trying to unit test some code using Mock. I would like to raise an exception, and test that the exception is caught and another function is called before it is re-raised
except exception as e:
car.create_log(car_details)
raise e
The unit test:
car = Car()
car.registrations.update = Mock()
car.registrations.update.side_effect = RegistrationError()
car.create_log = Mock()
car.register_car('123123')
car.create_log.assert_called_once()
self.assertRaises(RegistrationError)
I can confirm the method throws an error but cannot test that the method create_log is called before the error is re-raised.
This is how you should use assertRaises:
with self.assertRaises(RegistrationError):
car.register_car('123123')
car.create_log.assert_called_once()
or you can pass it a callable and arguments:
self.assertRaises(RegistrationError, car.register_car, '123123')
Related
I am trying to test the exception block of a simple python function as follows
function_list.py
def option_check():
"""
Function to pick and return an option
"""
try:
# DELETE_FILES_ON_SUCCESS is a config value from constants class. Valid values True/False (boolean)
flag = Constants.DELETE_FILES_ON_SUCCESS
if flag:
return "remove_source_file"
else:
return "keep_source_file"
except Exception as error:
error_message = F"task option_check failed with below error {str(error)}"
raise Exception(f"Error occured: {error}") from error
How do I force and exception to unit test the exception block? Please note that what I have here in exception block is a simplified version of what I actually have. What I am looking for is a way to force an exception using unit test to test the exception scenarios.
Python version is 3.6
You could patch the Constants class and delete the attribute you access from the mock.
from unittest import mock
# replace __main__ with the package Constants is from
with mock.patch("__main__.Constants") as mock_constants:
del mock_constants.DELETE_FILES_ON_SUCCESS
option_check()
When option_check() tries to access Constants.DELETE_FILES_ON_SUCCESS, it will raise an AttributeError, allowing you to reach the except block.
What I have done :
I have a function def get_holidays(): which raises a Timeout error. My test function test_get_holidays_raises_ioerror(): first sets requests.get.side_effect = IOError and then uses pytest.raises(IOError) to assert if that function raises an IOError.
What the issue is :
Ideally this should fail, since my actual get_holidays() does not raise an IOError. But the test passes.
Possible reason :
This might be because Timeout is inherited from the IOError class.
What I want :
Want to assert specifically if IOError is raised.
Code :
from mock import Mock
import requests
from requests import Timeout
import pytest
requests = Mock()
# Actual function to test
def get_holidays():
try:
r = requests.get('http://localhost/api/holidays')
if r.status_code == 200:
return r.json()
except Timeout:
raise Timeout
return None
# Actual function that tests the above function
def test_get_holidays_raises_ioerror():
requests.get.side_effect = IOError
with pytest.raises(IOError):
get_holidays()
pytest captures the exception in an ExceptionInfo object. You can compare the exact type after the exception.
def test_get_holidays_raises_ioerror():
requests.get.side_effect = IOError
with pytest.raises(IOError) as excinfo:
get_holidays()
assert type(excinfo.value) is IOError
So, I have the most trivial in the world example. This is my class to be tested:
# My_Class.py
class My_Class(object):
#staticmethod
def doit(name, params):
try:
raise Exception("This is my error message")
except Exception:
print("Exception: I raised Exception")
And this is the tester itself:
# test.py
import unittest
from My_Class import My_Class
class Test_MyClass(unittest.TestCase):
def setUp(self):
self.my_class = My_Class()
def test_my_class(self):
name = "Abrakadabra"
params = {}
self.assertRaises(Exception, self.my_class.doit, name, params)
And this is what I see in the console, when I'm running my test.py:
$ nosetests test.py
F
======================================================================
FAIL: test_my_class (test.Test_MyClass)
----------------------------------------------------------------------
Traceback (most recent call last):
File ....
nose.proxy.AssertionError: Exception not raised by doit
-------------------- >> begin captured stdout << ---------------------
Exception: I raised Exception
--------------------- >> end captured stdout << ----------------------
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)
It is reaaly iteresting, because it is controversial. On the one hand the test says that "Exception not raised by doit", but one line below it clearly prints out a message from the Exception block. So, what I'm doing wrong here??? Thanks!
To directly answer your question, the reason why you are getting that message is because with this assertion:
self.assertRaises(Exception, self.my_class.doit, name, params)
You are testing to make sure an exception was raised. But your try/except suppresses this. If you actually remove your try/except your test will in fact pass, because now your method will raise.
Since you do not want to do this, what you should be doing instead is testing the behaviour of your method when an exception is raised. Ultimately, you want to make sure that your print method is called in your except. I have put together an example below to help understand this.
Keeping in mind what #user2357112 mentioned, which is very important to keep in mind when unittesting, here is an example to help expand on that to provide a practical use for what you are trying to do:
Let us just put together some method:
def some_method():
pass
We will now put this in to your staticmethod you defined as such:
# My_Class.py
class My_Class(object):
#staticmethod
def doit(name, params):
try:
some_method()
except Exception:
print("Exception: I raised Exception")
So now, when it comes to your unittesting, you want to test the behaviour of your method doit. With that in mind, what you will do in this case, is test that some_method will raise an exception and you will validate how your doit method behaves to that exception being raised.
At this point, I suggest taking a look at the documentation behind unittest and mock to get more familiar with what you can do with your testing, but here is an example using mock patching to test the behaviour of your code if an exception is being raised:
#patch('builtins.print')
#patch('__main__.some_method')
def test_my_class(self, m_some_method, m_print):
name = "Abrakadabra"
params = {}
# have the side_effect raise the exception when some_method is called in doit
m_some_method.side_effect = Exception()
self.my_class.doit(name, params)
# check to make sure you caught the exception by checking print was called
self.assertEqual(m_print.call_count, 1)
When you put it all together, the following is functional code that I ran on my end that you can play around with to understand what is happening:
def some_method():
pass
# My_Class.py
class My_Class(object):
#staticmethod
def doit(name, params):
try:
some_method()
except Exception:
print("Exception: I raised Exception")
# test.py
import unittest
from mock import patch
class Test_MyClass(unittest.TestCase):
def setUp(self):
self.my_class = My_Class()
#patch('builtins.print')
#patch('__main__.some_method')
def test_my_class(self, m_some_method, m_print):
name = "Abrakadabra"
params = {}
m_some_method.side_effect = Exception()
self.my_class.doit(name, params)
self.assertEqual(m_print.call_count, 1)
if __name__ == '__main__':
unittest.main()
assertRaises is an assertion about the function's visible behavior, not its internals. It asserts that the stated exception passes out of the function. Any exceptions that are handled inside the function are not assertRaises's concern.
assertRaises failed since there was actually no exception raised. Well, it was raised but handled with except inside the doit() method. The problem is here:
try:
raise Exception("This is my error message")
except Exception:
print("Exception: I raised Exception")
You are raising an exception and then catching it without re-raising. From a caller (assertRaises is the caller in your case) perspective, no errors were thrown during the function call. Re-raising an exception allows a caller to handle an exception as well. Put a raise after the print:
try:
raise Exception("This is my error message")
except Exception:
print("Exception: I raised Exception")
raise # re-raising
Also see Handling Exceptions.
I have a function (foo) which calls another function (bar). If invoking bar() raises an HttpError, I want to handle it specially if the status code is 404, otherwise re-raise.
I am trying to write some unit tests around this foo function, mocking out the call to bar(). Unfortunately, I am unable to get the mocked call to bar() to raise an Exception which is caught by my except block.
Here is my code which illustrates my problem:
import unittest
import mock
from apiclient.errors import HttpError
class FooTests(unittest.TestCase):
#mock.patch('my_tests.bar')
def test_foo_shouldReturnResultOfBar_whenBarSucceeds(self, barMock):
barMock.return_value = True
result = foo()
self.assertTrue(result) # passes
#mock.patch('my_tests.bar')
def test_foo_shouldReturnNone_whenBarRaiseHttpError404(self, barMock):
barMock.side_effect = HttpError(mock.Mock(return_value={'status': 404}), 'not found')
result = foo()
self.assertIsNone(result) # fails, test raises HttpError
#mock.patch('my_tests.bar')
def test_foo_shouldRaiseHttpError_whenBarRaiseHttpErrorNot404(self, barMock):
barMock.side_effect = HttpError(mock.Mock(return_value={'status': 500}), 'error')
with self.assertRaises(HttpError): # passes
foo()
def foo():
try:
result = bar()
return result
except HttpError as error:
if error.resp.status == 404:
print '404 - %s' % error.message
return None
raise
def bar():
raise NotImplementedError()
I followed the Mock docs which say that you should set the side_effect of a Mock instance to an Exception class to have the mocked function raise the error.
I also looked at some other related StackOverflow Q&As, and it looks like I am doing the same thing they are doing to cause and Exception to be raised by their mock.
https://stackoverflow.com/a/10310532/346561
How to use Python Mock to raise an exception - but with Errno set to a given value
Why is setting the side_effect of barMock not causing the expected Exception to be raised? If I am doing something weird, how should I go about testing logic in my except block?
Your mock is raising the exception just fine, but the error.resp.status value is missing. Rather than use return_value, just tell Mock that status is an attribute:
barMock.side_effect = HttpError(mock.Mock(status=404), 'not found')
Additional keyword arguments to Mock() are set as attributes on the resulting object.
I put your foo and bar definitions in a my_tests module, added in the HttpError class so I could use it too, and your test then can be ran to success:
>>> from my_tests import foo, HttpError
>>> import mock
>>> with mock.patch('my_tests.bar') as barMock:
... barMock.side_effect = HttpError(mock.Mock(status=404), 'not found')
... result = my_test.foo()
...
404 -
>>> result is None
True
You can even see the print '404 - %s' % error.message line run, but I think you wanted to use error.content there instead; that's the attribute HttpError() sets from the second argument, at any rate.
How do I test my parameter if it will raise an exception without actually raising it, using try and except?
class MyClass:
def function(parameter):
pass
parameter is an ambiguous function that may raise 1 or more of any exception, for example:
parameter = pow("5", 5)
A TypeError is raised as soon as the function is called and before the function can execute its statements.
In a comment to another answer you said: "parameter is another function; take for example: parameter = pow("5", 5) which raises a TypeError, but it could be any type of function and any type of exception."
If you want to catch the exeption inside your function you have to call the paramenter (which I'm assuming is callable) inside that function:
def function(callable, args=()):
try:
callable(*args)
except:
print('Ops!')
Example:
>>> function(pow, args=("5", 5))
Ops!
This is if you really need to call your "paramenter" inside the function. Otherwise your should manage its behaviour outside, maybe with something like:
>>> try:
... param = pow('5', 5)
... except:
... param = 10
...
>>> param
10
>>> function(param)
In this example, to raise an exception is pow not function, so it's a good practice to separate the the two different call, and wrap with a try-except statement the code that might fail.
From what I can understand, you want to handle the exceptions raised and also inspect what sort of errors were raised for further inspection? Here is one way of doing it.
class Foo(object):
def find_errors(arg):
errors = []
try:
# do something
except TypeError as e:
errors.append(e)
# handle exception somehow
except ValueError as e:
errors.append(e)
# handle exception somehow
# and so on ...
finally:
pass #something here
return errors, ans
Now you can inspect errors and find out what exceptions have been raised.
If you expect the parameter to be a certain type, you can use type(paramter) is parametertype.
For example, if you wanted to verify that 'i' is an int, run instructions if(type(i) is int):
By edit:
try:
pow("5",5)
return 0
except Exception, err:
sys.stderr.write('ERROR: %s\n' % str(err))
return 1
Perhaps what you mean is how to catch the TypeError exceptions caused by invalid function calls?
Like this:
def foo(bar):
pass
foo(1, 2)
You don't catch them in the function and certainly not in the def foo(bar): line.
It's the caller of the function that made an error so that's where you catch the exception:
try:
foo(1, 2)
except TypeError:
print('call failed')