Question

Does 100% statement coverage is adequate for testing criteria? What can go wrong even if we achieve 100% statement coverage? Please explain with an example.  

Answer 1

100% statement coverage is not at all adequate for testing criteria and it is a big misconception that a code with 100% statement coverage has a very good code quality.It measures whether the test cases execute the code or not .They are least bothered about the effectiveness of the test and thus the content of the code is not properly explored.

Even if we achieve 100% statement  coverage the following can go wrong:-

1)Simple IF statements

2)Exception Handling

3)Incorrect test cases that are just making the statement covered.

4)Missing of functionality

5)Logical Operators

6)Loop termination

For example:-

class Quantity(object):

    def __init__(self, measure):
if measure == "Large" :
self.take = "Enough!"
if measure == "Small" :
self.take = "Hungry"

def test_missing(self):
#missing a test for medium quantity   

    l = Quantity("Large")
self.assertEqual( l.take, "Enough" )
s = Quantity("Small")
self.assertEqual( s.take, "Hungry" )

In the above example the medium size quantity is missing but still the statement coverage is 100% since all the code has been covered.Thus 100% statement coverage does not implies that all the functionality has been addressed,there may be a missing functionality.