Develop Reference

How to test for raised exception in Python/Django?

I've got a Django project in which I have a function which I want to test. Simplified, the function looks like this:
class InvalidUrlError(Exception):
pass
def get_info_from_url(url):
try:
return url.split(':')[1].split('/')[0]
except Exception:
raise InvalidUrlError(f"Invalid url: {url}")
And my test looks like this:
class ToolsTestCase(TestCase):
def test_get_info_from_url_wrong_formatted_url(self):
self.assertRaises(InvalidUrlError, get_info_from_url("https://acc.images.data.ourcompany.com/"))
When I run it though, I get the following output:
$ ./manage.py test
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
....E
======================================================================
ERROR: test_get_info_from_url_wrong_formatted_url (checker.tests.ToolsTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/kramer65/repos/auth-proxy/app/checker/tools.py", line 10, in get_info_from_url
return url.split(':')[1].split('/')[0]
IndexError: list index out of range
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/kramer65/repos/auth-proxy/app/checker/tests.py", line 57, in test_get_info_from_url_wrong_formatted_url
self.assertRaises(InvalidUrlError, get_info_from_url("https://acc.images.data.ourcompany.com/"))
File "/home/kramer65/repos/auth-proxy/app/checker/tools.py", line 15, in get_info_from_url
raise InvalidUrlError(f"Invalid url: {url}")
checker.tools.InvalidUrlError: Invalid url: https://acc.images.data.ourcompany.com/
----------------------------------------------------------------------
Ran 5 tests in 0.037s
FAILED (errors=1)
Destroying test database for alias 'default'...
Why does it raise the exceptions, instead of passing the tests? I think I do a comparable thing in another test, which works great.
Does anybody know what I'm doing wrong here?

You need to pass a callable instead of calling the function itself. Unittest docs for assertRaises
So change it to:
class ToolsTestCase(TestCase):
def test_get_info_from_url_wrong_formatted_url(self):
self.assertRaises(InvalidUrlError, get_info_from_url, "https://acc.images.data.ourcompany.com/")
Other option is to use assertRaises as context manager like this:
class ToolsTestCase(TestCase):
def test_get_info_from_url_wrong_formatted_url(self):
with self.assertRaises(InvalidUrlError):
get_info_from_url("https://acc.images.data.ourcompany.com/")

How to get a single outcome from each python unit-test module

I have different unit_test modules which are included by unit test codes as you'll see:
import unittest
class TestTest(unittest.TestCase):
def setUp(self):
pass
def tearDown(self):
pass
def test_type(self):
self.assertTrue(False)
if __name__ == "__main__":
unittest.main()
I need to get the result of each module after running it and write it in the database. So I expect 3 different outcomes after running each module:
PASSED
NOTPASSED
WORKING
But the problem is after running the test module I get such a output.
F
======================================================================
FAIL: test_test (main.TestTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/~/mytest.py", line 12, in test_test
self.assertTrue(False)
AssertionError: False is not true
----------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (failures=1)
I don't know if there is something in unittest to give me a straight value as I expect?
I also tried this:
TestTest = unittest.TestLoader().loadTestsFromTestCase(TestTest)
suit = unittest.TestSuite([TestTest])
result = unittest.TextTestRunner(verbosity=2).run(suit)
print(result)
But it gives me this:
test_test (main.TestTest) ... FAIL
======================================================================
FAIL: test_test (__main__.TestTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/~/mytest.py", line 12, in test_test
self.assertTrue(False)
AssertionError: False is not true
----------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (failures=1)

Basically if you need in your test results more information just add the keyword msg documenting the test, for example:
self.assertTrue(False, msg = 'Host connection not stablished.')

How do you show an error message when a test does not throw an expected exception?

I am new to Python. I wanted to test if my code threw an exception. I got the code from How do you test that a Python function throws an exception?
import mymod
import unittest
class MyTestCase(unittest.TestCase):
def test1(self):
self.assertRaises(SomeCoolException, mymod.myfunc, compulsory_argument)
Now, I also want to display a message if the exception is not thrown. How do I do that? The Python documentation does not mention it clearly. I added the message after "compulsory_argument" and it failed.
I tried the first answer with modifications and got an exception. What is my mistake here?
import unittest
def sayHelloTo(name):
print("Hello " + name)
class MyTestCase(unittest.TestCase):
def test1(self):
person = "John"
with self.assertRaises(Exception, "My insightful message"):
sayHelloTo(person)
Error:
Error
Traceback (most recent call last):
File "C:\tests\tester.py", line 9, in test1
with self.assertRaises(Exception, "My insightful message"):
AttributeError: __exit__

As of Python 3.3, assertRaises can be used as a context manager with a message:
import unittest
def sayHelloTo(name):
print("Hello " + name)
class MyTestCase(unittest.TestCase):
def test1(self):
person = "John"
with self.assertRaises(Exception, msg="My insightful message"):
sayHelloTo(person)
if __name__ == "__main__":
unittest.main()
It results in
Hello John
F
======================================================================
FAIL: test1 (__main__.MyTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "r.py", line 10, in test1
sayHelloTo(person)
AssertionError: Exception not raised : My insightful message
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)

Now, I also want to display a message if the exception is not thrown. How do I do that ?
The general philosophy of unittest is for the tests to be silent when they succeed and only become verbose when they fail. Accordingly, the API provides a "msg" keyword argument for the unsuccessful case but does not offer an alternative for the successful case.
That said, another part of the philosophy works in your favor. In general, test cases internally raise an exception when a testcase fails. That means that if you want to display a message when there is a success, you just add another statement after the test:
with self.assertRaises(TypeError, msg='Oh no, I did not get a TypeError')
somecode()
logging.info('Yippee, we got a TypeError!') # Runs after a successful test

Nose: generator for TestCase-based classes

I want to create a generator for variations of a TestCase-derived class.
What I tried is this:
import unittest
def create_class(param):
class Test(unittest.TestCase):
def setUp(self):
pass
def test_fail(self):
assert False
return Test
def test_basic():
for i in range(5):
yield create_class(i)
What I get is this:
======================================================================
ERROR: test_1.test_basic
----------------------------------------------------------------------
Traceback (most recent call last):
File "/usr/lib/python3.3/site-packages/nose/case.py", line 268, in setUp
try_run(self.test, names)
File "/usr/lib/python3.3/site-packages/nose/util.py", line 478, in try_run
return func()
TypeError: setUp() missing 1 required positional argument: 'self'
Yielding instances instead of classes (yield create_class(i)()) leaves me with this error:
======================================================================
ERROR: test_1.test_basic
----------------------------------------------------------------------
Traceback (most recent call last):
File "/usr/lib/python3.3/site-packages/nose/case.py", line 198, in runTest
self.test(*self.arg)
File "/usr/lib/python3.3/unittest/case.py", line 492, in __call__
return self.run(*args, **kwds)
File "/usr/lib/python3.3/unittest/case.py", line 423, in run
testMethod = getattr(self, self._testMethodName)
AttributeError: 'Test' object has no attribute 'runTest'
Any ideas?

When instantiating a TestCase you should pass the method name of the test:
yield create_class(i)('test_fail')
Otherwise the name defaults to runTest(and thus the last error you got).
Also note that there is a strange interaction between test generators and TestCase. With the following code:
import unittest
def create_class(param):
class Test(unittest.TestCase):
def setUp(self):
pass
def test_fail(self):
print('executed')
assert False
print('after assert')
return Test
def test_basic():
for i in range(5):
yield create_class(i)('test_fail')
I obtain this output:
$ nosetests -s
executed
.executed
.executed
.executed
.executed
.
----------------------------------------------------------------------
Ran 5 tests in 0.004s
OK
As you can see the test does not fail, even though the assert works. This is probably due to the fact that TestCase handles the AssertionError but nose does not expect this to be handled and thus it cannot see that the test failed.
This can be seen from the documentation of TestCase.run:
Run the test, collecting the result into the test result object passed as result. If result is omitted or None, a temporary result
object is created (by calling the defaultTestResult() method) and
used. The result object is not returned to run()‘s caller.
The same effect may be had by simply calling the TestCase instance.
So, nose doesn't see that the objected yielded by the generator is a TestCase which should be handled in a special manner, it simply expects a callable. The TestCase is run, but the result is put into a temporary object that is lost, and this eats all test failures that happen inside the tests. Hence yielding TestCasees simply doesn't work.

I have run the codes you provides. I received no error. The version I use is python2.7. System is ubuntu12.10. Maybe you need to check with python2.7.

nose plugin for expected-failures

Is there an existing plugin which could be used like:
#nose.plugins.expectedfailure
def not_done_yet():
a = Thingamajig().fancynewthing()
assert a == "example"
If the test fails, it would appear like a skipped test:
$ nosetests
...S..
..but if it unexpected passes, it would appear similarly to a failure, maybe like:
=================================
UNEXPECTED PASS: not_done_yet
---------------------------------
-- >> begin captured stdout << --
Things and etc
...
Kind of like SkipTest, but not implemented as an exception which prevents the test from running.
Only thing I can find is this ticket about supporting the unittest2 expectedFailure decorator (although I'd rather not use unittest2, even if nose supported it)

I don't know about a nose plugin, but you could easily write your own decorator to do that. Here's a simple implementation:
import functools
import nose
def expected_failure(test):
#functools.wraps(test)
def inner(*args, **kwargs):
try:
test(*args, **kwargs)
except Exception:
raise nose.SkipTest
else:
raise AssertionError('Failure expected')
return inner
If I run these tests:
#expected_failure
def test_not_implemented():
assert False
#expected_failure
def test_unexpected_success():
assert True
I get the following output from nose:
tests.test.test_not_implemented ... SKIP
tests.test.test_unexpected_success ... FAIL
======================================================================
FAIL: tests.test.test_unexpected_success
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\Python32\lib\site-packages\nose-1.1.2-py3.2.egg\nose\case.py", line 198, in runTest
self.test(*self.arg)
File "G:\Projects\Programming\dt-tools\new-sanbi\tests\test.py", line 16, in inner
raise AssertionError('Failure expected')
AssertionError: Failure expected
----------------------------------------------------------------------
Ran 2 tests in 0.016s
FAILED (failures=1)

Forgive me if I've misunderstood, but isn't the behavior you desire provided by core python's unittest library with the expectedFailure decorator, which is—by extension—compatible with nose?
For an example of use see the docs and a post about its implementation.

You can do it with one of two ways:
nose.tools.raises decorator
from nose.tools import raises
#raises(TypeError)
def test_raises_type_error():
raise TypeError("This test passes")
nose.tools.assert_raises
from nose.tools import assert_raises
def test_raises_type_error():
with assert_raises(TypeError):
raise TypeError("This test passes")
Tests will fail if exception is not raised.
Yup, I know, asked 3 years ago :)