Why is this true? 100% path coverage can require more test cases than 100% statement coverage of the same code.

[larrylawl]

Lecture 7 Quiz Part 2
Aren't paths a subset of statements? Thus if you have executed all statements, you would have executed all the paths.

[danielwys]

This was previously talked about in #134 and I’ll reproduce my answer below:

I think this is best illustrated with an example.

Let's say we have a while loop that can loop up to 100 times.

For us to achieve a 100% statement coverage - we just need to test one iteration of the while loop. That executes all the statements within the while loop's code block - thereby achieving full statement coverage.

To achieve full path coverage, we have to test for every possible path - that means that we test the while loop for 1, 2, 3 ... 99, 100 iterations each time, to ensure that it produces the correct result each time. That's a far more comprehensive test, and only when all paths have been exhausted through testing can it be considered full path coverage. And definitely a lot more work to be done, testing-wise.

This applies to any form of conditionals or loops within a program - you'd have to test all possible number of iterations and/or all possible branches to ensure 100% path coverage, as compared to once for statement coverage.

Hope that illustrates it for you!

[larrylawl]

Got it, thanks !