Why is the code not passing the unittest?

Question

This is the code:

# mean_var-_std.py
def calculate(list):
    if len(list) < 9:
        print("List must contain nine numbers.")
        raise ValueError
    else:
        return 0

This is the unit-test:

import unittest
import mean_var_std


# the test case
class UnitTests(unittest.TestCase):
    def test_calculate_with_few_digits(self):
        self.assertRaisesRegex(ValueError, "List must contain nine numbers.", mean_var_std.calculate, [2,6,2,8,4,0,1,])

if __name__ == "__main__":
    unittest.main()

This is the error that I get:

F
======================================================================
FAIL: test_calculate_with_few_digits (test_module.UnitTests)
----------------------------------------------------------------------
ValueError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/runner/fcc-mean-var-std-2/test_module.py", line 8, in test_calculate_with_few_digits
    self.assertRaisesRegex(ValueError, "List must contain nine numbers.", mean_var_std.calculate, [2,6,2,8,4,0,1,])
AssertionError: "List must contain nine numbers." does not match ""

----------------------------------------------------------------------
Ran 1 test in 0.004s

FAILED (failures=1)

I don't understand what AssertionError: "List must contain nine numbers." does not match "" means. How can I solve this problem? Thanks in advance.

Konrad Rudolph · Accepted Answer · 2020-08-30 17:43:00Z

2

Your function raises an error without error message. It also prints a message but that’s unrelated (and generally seen as bad practice).

Remove the print statement and raise an error with an error message to fix the unit test failure:

def calculate(list):
    if len(list) < 9:
        raise ValueError("List must contain nine numbers.")
    else:
        return 0

answered Aug 30, 2020 at 17:43

Konrad Rudolph

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Comments

Hatem Saadallah · Accepted Answer · 2020-08-30 17:49:36Z

0

Here's a small modification in the code.

def calculate(list):
    if len(list) < 9:
        print("List must contain nine numbers.")
        raise ValueError("List must contain nine numbers.")
    else:
        return 0

Since you're looking for ValueError, the unittest will not look at your print statement.

answered Aug 30, 2020 at 17:49

Hatem Saadallah

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