In which cases should a unit test be terminated with an error?

A modular test should be marked as failed when the functionality being tested does not meet the expected result. This means that the test has detected a bug or incorrect behavior in the code.

For example, if a function is supposed to return the sum of two numbers but returns a different value, the test should fail.

In Python, using unittest or pytest, this happens automatically if an assert fails:

def test_sum():
    result = sum([1, 2, 3])
    assert result == 6  # if result != 6, the test will fail

You can manually fail a test using exceptions or assert when conditions are not met. This helps identify and fix issues early in the development process.