Python unittest - opposite of assertRaises?

Question

I want to write a test to establish that an Exception is not raised in a given circumstance.

It\'s straightforward to test if an Exception is raise

Answer 1

One straight forward way to ensure the object is initialized without any error is to test the object's type instance.

Here is an example :

p = SomeClass(param1=_param1_value)
self.assertTrue(isinstance(p, SomeClass))

Answer 2

you can try like that. try: self.assertRaises(None,function,arg1, arg2) except: pass if you don't put code inside try block it will through exception' AssertionError: None not raised " and test case will be failed. Test case will be pass if put inside try block which is expected behaviour.

Answer 3

I've found it useful to monkey-patch unittest as follows:

def assertMayRaise(self, exception, expr):
  if exception is None:
    try:
      expr()
    except:
      info = sys.exc_info()
      self.fail('%s raised' % repr(info[0]))
  else:
    self.assertRaises(exception, expr)

unittest.TestCase.assertMayRaise = assertMayRaise

This clarifies intent when testing for the absence of an exception:

self.assertMayRaise(None, does_not_raise)

This also simplifies testing in a loop, which I often find myself doing:

# ValueError is raised only for op(x,x), op(y,y) and op(z,z).
for i,(a,b) in enumerate(itertools.product([x,y,z], [x,y,z])):
  self.assertMayRaise(None if i%4 else ValueError, lambda: op(a, b))

Answer 4

Just call the function. If it raises an exception, the unit test framework will flag this as an error. You might like to add a comment, e.g.:

sValidPath=AlwaysSuppliesAValidPath()
# Check PathIsNotAValidOne not thrown
MyObject(sValidPath)