A difference between statement and decision coverage

Statement coverage is said to make sure that every statement in the code is executed at least once.
Decision/branch coverage is said to test that each branch/output of a decisions is tested, i.e. all statements in both false/true branches will be executed.
But is it not the same? In Statement coverage I need to execute all statements so I guess it can be only done by running all possible ways. I know I am missing something here..

11.5k 26 26 gold badges 107 107 silver badges 175 175 bronze badges asked Jan 25, 2013 at 10:00 5,015 15 15 gold badges 42 42 silver badges 67 67 bronze badges

I guess this question is better for Programmers.StackExchange.com. By the way decision and branch coverage are not the same thing!

Commented Jan 25, 2013 at 10:03 @Adriano Yes, wiki says so but a lot of other sources say it is the same. Commented Jan 25, 2013 at 10:09

Not just wiki, formal definition for "decision" is each condition to enter the code path of a branch (then branch is the whole condition). Imagine, for example, the short circuit in C/C++. You may decide to use them as synonyms or not.

Commented Jan 25, 2013 at 10:15

Moreover a statement may not be executed even if the branch where it is has been executed because of, for example, jumps, exceptions and/or other asynchronous conditions (locks, signals, events). That's why decision coverage and statement coverage may differ.

Commented Jan 25, 2013 at 10:18

5 Answers 5

The answer by Paul isn't quite right, at least I think so (according to ISTQB's definitions). There's quite a significant difference between statement, decision/branch, and condition coverage. I'll use the sample from the other answer but modify it a bit, so I can show all three test coverage examples. Tests written here give 100% test coverage for each type.

if (a || b) < test1 = true; >else < if (c) < test2 = true; >>

We have two statements here - if(a||b) and if(c), to fully explain those coverage differences:

statement coverage has to test each statement at least once, so we need just two tests:

a=true and b=false - that gives us path if(a||b) true -> test1 = true
a=false, b=false and c=true - that gives us path: if(a||b) false -> else -> if(c) true -> test2 = true

This way we executed each and every statement.

branch/decision coverage needs one more test:

a=false, b=false, and c=false - that leads us to that second if but we are executing the false branch from that statement, that wasn't executed in statement coverage

That way we have all the branches tested, meaning we went through all the paths. 3. condition coverage needs another test:

a=false, b=true - that leads through the same path as the first test but executes the other decision in OR statement (a||b) to go through it.

That way we have all conditions tested, meaning that we went through all paths (branches) and triggered it with each condition we could - the first 'if' statement was true in the first test because a=true triggered it and in the last test because b=true triggered it. Of course, someone can argue that case with a=true and b=true should be tested as well, but when we check how 'or' works then we can see it isn't needed and also variable c can be of any value as in those tests it is not evaluated.

At least I interpreted it this way. If someone is still interested :)

EDIT: In most sources, I found lately decision/branch coverage terms are equivalent, and the term I described as decision coverage is in fact condition coverage hence that update of the answer.