What is a proper way to test SQLAlchemy code that throw IntegrityError?

Question

I have read this Q&A, and already try to catch exception on my code that raise an IntegrityError exception, this way :

self.assertRaises(IntegrityError, db.session.commit())

But somehow my unit test still failed and stop with IntegrityError exception. I expect it to say OK as I already expect to have exception in my unit test. This was cause by code that tries to insert row having the same unique field values.

Any idea?

Answer 1

One of these will to the trick:

# ... only if version >= 2.7
with self.assertRaises(IntegrityError):
    db.session.commit()

Or:

self.assertRaises(IntegrityError, db.session.commit)

The difference between your example and the correct way is:

# Your example: You call db.session.commit(), this will raise an exception before
# assertRaises is called
self.assertRaises(IntegrityError, db.session.commit())

# Correct way: Pass what should be called to assertRaises, 
# let assertRaises invoke it and check for exception
self.assertRaises(IntegrityError, db.session.commit)

I prefer to use assertRaises as a context manager (using with).