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+And this criterion is called Modified Condition/Decision Coverage,
+
+2
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+also called MC/DC. This criterion is very important because
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+it is often required for safety critical applications.
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+For example, the FAA, the Federal Aviation Administration, requires
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+for all the software that runs on commercial
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+6
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+airplanes to be tested according to the Modified Condition/Decision
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+Coverage. So what is the key idea behind the
+
+8
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+MC/DC criterion? It is to test only the important
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+9
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+combinations of conditions instead of all of them, and limit
+
+10
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+the testing cost by excluding the other combinations. And the way
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+11
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+in which it works is by extending branch and decision
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+12
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+coverage with the requirement that each condition should affect the decision
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+outcome independently. So let's see what this means with an
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+example that will also show you how you can reduce the
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+15
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+number of combinations in this way. I am going to
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+show you an example of how MC/DC works using this predicate
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+which consists of three conditions. a, b, and c, which are all
+
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+in and, so the overall predicate is a and b and c.
+
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+The first thing I'm going to do is to show you how
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+many test cases we will need to satisfy the multiple condition coverage
+
+21
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+for this simple predicate. Which means, how many test cases we will
+
+22
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+need to test all the possible combinations of true and false values
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+for these conditions. So I'm going to populate this table. And as you
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+24
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+can see, at the end we have eight test cases. Each test case
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+tests a different combination of values for a, b, and c.
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+I'm also showing, for each test case, the outcome of the overall
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+predicate. So, for example, if we look at the first one, the
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+first test case, will be such that a is true, b is
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+true, and c is true. And therefore, the overall outcome of
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+the predicate is true. Now lets consider the first condition, a. As
+
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+I said a minute ago, what we want to test are the
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+important combination. Which are the comibatinos
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+in which a single condition independently
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+effects the outcome of the overall predicate. So if we consider a
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+and we look at this possible set of this cases. Let's try to
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+find two test cases such that the only difference between the two
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+test cases is the value of a, and the overall outcome of the
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+predicate is different. If we look at the table, we can see
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+that this is true for test cases one and five. If we look
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+at these two cases, we can see that the overall of the predicate
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+in the two cases is true and false, and that the only difference
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+between the value of the conditions in the value of a. So
+
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+these test cases satisfy exactly what we wanted. There are two test
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+cases in which the value of a independently decides the overall value
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+of the predicate. What we do, therefore, is to add these first
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+two test cases to our set of tests down here. Now let's
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+focus on b and let's try to find two test cases such
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+that the value of b is the only value that changes between
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+the two test cases, but the overall value of the predicate is
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+different, the same thing we did for a. And in this case,
+
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+we can see that if we select test case number one, and test
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+case number three, we have exactly that situation. b is true in the
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+first case, false in the second one, a and c don't change, but
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+the overall value of the predicate changes. And now you can notice
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+something else. That even though we selected two test cases, tested two values,
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+one we already had. So, we only need three test cases overall to
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+test a and b according to MC/DC. Now, let's look at our last
+
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+condition, c. At this point, we know the game, so we
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+just have to look for two test cases that satisfy our
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+requirements. And in this case, one and two are suitable candidates.
+
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+And once more, because we already have one, we just have to
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+add two to our list. So as you can see from
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+this example, we went from having eight test cases needed to cover
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+all the possible combinations of conditions to only four test cases
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+to satisfy the MC/DC criteria. So let's see where MC/DC stands in
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+our substantion hierarchy. This is what we had so far
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+in the hierarchy and this is where the MC/DC criterion will
+
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+stand. MC/DC criterion is stronger than branch and condition coverage.
+
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+Why? Because it requires every single condition to be true and
+
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+false. And therefore, this section was a condition coverage criteria.
+
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+And it also requires every predicate to be true and false
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+and therefore, this section is branch coverage. And in addition,
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+it's got the additional requirements that the true and false values,
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+all the conditions have to also decide the overall
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+value of the predicate. So it's stronger. Which is more
+
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+thorough than branch and condition coverage and, as usual,
+
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+also stronger than branch coverage, statement coverage, and condition coverage.