Python unit testing, error happened and exception matched, but my program returns an `AssertionError`

Question

Here is my Python code.

try: ct("table_that_does_not_exist", "database_that_does_not_exists")
except r.errors.ReqlOpFailedError as e: self.fail()

ct is a function to check if a table is exist in a database. ct returns True if a table exists in the database and False for otherwise.

try: ct("table_that_does_not_exist", "database_that_does_not_exists") is trying to check a non-existent table in a non-existent database. This should returns an error of this.

rethinkdb.errors.ReqlOpFailedError: Database `database_that_does_not_exists` does not exist in:
r.db('database_that_does_not_exists').table_list().contains('table_that_does_not_exist')

However, the error is somewhat not capture in except r.errors.ReqlOpFailedError as e: self.fail() and returns an AssertionError.

I expect this to pass the test, since ct("table_that_does_not_exist", "database_that_does_not_exists") will return r.errors.ReqlOpFailedError. But I got this instead.

======================================================================
FAIL: test_check_table (__main__.test)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test.py", line 61, in test_check_table
    try: ct("table_that_does_not_exist", "database_that_does_not_exists")
rethinkdb.errors.ReqlOpFailedError: Database `database_that_does_not_exists` does not exist in:
r.db('database_that_does_not_exists').table_list().contains('table_that_does_not_exist')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                   

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 62, in test_check_table
    except r.errors.ReqlOpFailedError as e: self.fail()
AssertionError

----------------------------------------------------------------------
Ran 7 tests in 0.050s

FAILED (failures=1)

The error is match but not proceed through except.

What is wrong with my test?

Hey there! I was following this, stackoverflow.com/questions/4319825/…. I am still learning unit testing in general. What I want is the is to pass the test if certain exception happens. In this case I want to pass the test if r.errors.ReqlOpFailedError happens. — notalentgeek
– notalentgeek, Commented Feb 7, 2017 at 20:31

Denis Olehov · Accepted Answer · 2017-02-07 20:21:16Z

1

I believe your general approach to this is incorrect. Your exception checking code should look like this:

with self.assertRaises(r.errors.ReqlOpFailedError):
    ct("table_that_does_not_exist", "database_that_does_not_exists")

answered Feb 7, 2017 at 20:21

Denis Olehov

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5 Comments

notalentgeek Over a year ago

Hey! This is solve my problem. But how can I have the something like "If an error is NOT happening, pass the test."?

Denis Olehov Over a year ago

just use the ct("table_that_does_exist", "database_that_does_exists") snippet without with self.asserRaises(...)? :)

notalentgeek Over a year ago

So no assertion necessary? I thought the point of unit testing in Python is that you need to refer back to those assert functions in unittest.TestCase. If I just use ct("table_that_does_exist", "database_that_does_exists") I can just do this in any class I want and not necessarily to be in a class that inherits from unittest.TestCase right?

Denis Olehov Over a year ago

if you are using unittest framework, I believe unittest.TestCase is necessary. But in pytest it's not. Regarding your question: you should find a way to "assert" that your table or database is actually exist. Something like self.assertTrue(table_exists), but how do you populate this table_exists variable is an open question.

notalentgeek Over a year ago

Hey there, I found that try: c()\except r.errors.ReqlDriverError as e: self.fail() is good way to check if a function went through. If exception happens then it automatically failed the test.

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