Commit 96dd62c3 authored by Thanassis Tsiodras's avatar Thanassis Tsiodras
Browse files

All done.

parent bd69a737
......@@ -20,6 +20,13 @@ condition: coverage_demo
./coverage_demo 2 1 1
$(MAKE) report
conditiondecision: coverage_demo
$(MAKE) clean
$(MAKE)
./coverage_demo 1 1 1
./coverage_demo 2 0 2
$(MAKE) report
mcdc: coverage_demo
$(MAKE) clean
$(MAKE)
......
To get 100% decision coverage every decision in the program must take all
possible outcomes at least once. Given that in the code we have two decisions,
we need test cases that make those decisions true and false. For example, we
could have the following test cases:
a=3, b=0, x=2 → a > 1 && b == 0 (T), a == 2 || x > 1 (T)
a=1, b=0, x=1 → a > 1 && b == 0 (F), a == 2 || x > 1 (F)
$ make decision
...
./coverage_demo 3 0 2
Decision 1 was true
Decision 2 was true
./coverage_demo 1 0 1
Decision 1 was false
Decision 2 was false
...
Both decisions are exercised to be both true and false.
But notice in the gcov annotated output that all stmts are executed (there are no `####`
reported in any source line in the gcov output, we have 100% statement coverage).
But there ARE branches that were never executed (because these conditions
were never exercised - e.g. `b` was always 0!
Now, if we want to get 100% condition coverage, every condition in a decision
in the program must take all possible outcomes at least once. In the code we
have 4 conditions `a > 1`, `b == 0`, `a == 2`, `x > 1`. We need test cases that make
all 4 of the conditions true and false. The previous test cases don’t suffice
because the condition `b == 0` is never evaluated to false. That could mean a
untested critical scenario that could have a bug. To satisfy condition coverage
we could have the following test cases:
a = 1, b = 0, x = 2 → a > 1(F), b == 0(T), a == 2(F), x > 1(T)
a = 2, b = 1, x = 1 → a > 1(T), b == 0(F), a == 2(T), x > 1(F)
$ make condition
...
./coverage_demo 1 0 2
Decision 1 was false
Decision 2 was true
./coverage_demo 2 1 1
Decision 1 was false
Decision 2 was true
Now each condition has been both true and false, but overall, decision 1
was NEVER true - because its two conditions were once FT, and once TF.
The gcov output indicates this, in (a) the stmt coverage is not 100% (notice
the ####) and (b) the branch coverage is also not 100%, since the FINAL
branch (the one that says in the object code, we've evaluated to true,
let's execute the action of the `if`) is also not executed.
Since both types of coverage are important and one does not guarantee
satisfying the other, in practice they are typically combined, and that is
called condition decision coverage. For this level of coverage we could have
the following test cases:
a = 1, b = 1, x = 1 → a > 1(F), b == 0(F), a == 2(F), x > 1(F)
a = 2, b = 0, x = 2 → a > 1(T), b == 0(T), a == 2(T), x > 1(T)
$ make conditiondecision
...
./coverage_demo 1 1 1
Decision 1 was false
Decision 2 was false
./coverage_demo 2 0 2
Decision 1 was true
Decision 2 was true
Now, notice that although these cases would provide both levels of coverage
some conditions are being masked and therefore never evaluated.
gcov indicates this, since there are branches that are still, never executed.
For example, `a = 1` masks the condition `b == 0` in the decision `(a > 1 && b == 0)`
because it makes the condition `a > 1` false and therefore the executable
doesn't need to evaluate the other condition to determine the outcome of the
AND expression. Hence the need of modifying the test cases to ensure the
coverage of masking conditions, and that's called modified condition decision
coverage (MCDC): every condition in a decision has been shown to independently
affect that decision’s outcome. The test cases below satisfy MCDC coverage and
therefore also satisfy decision coverage and condition coverage:
a = 2, b = 0, x = 1 → a > 1 && b == 0 (T), a == 2 || x > 1 (T)
a = 3, b = 1, x = 2 → a > 1 && b == 0 (F), a == 2 || x > 1 (T)
a = 1, b = 0, x = 1 → a > 1 && b == 0 (F), a == 2 || x > 1 (F)
$ make mcdc
All statements executed, all gcov-reported branches executed.
*Based on [a nice (but buggy) Quora article](https://www.quora.com/What-is-the-difference-between-decision-coverage-and-condition-coverage-when-it-comes-to-code-coverage).*
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