Low code coverage doesn't always mean low test confidence

Code coverage is not always the best indicator of a test suite's usefulness, expressiveness, etc.

Contrary to the popular belief, there are cases in which high test coverage is not a good measure of test quality. In fact, high test coverage is not always possible.

Consider the following situation:

public class Container {
object a_1;
object b_1;
object c_1;
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object z_1;

public object A_1{
get
{
return a_1;
}
set
{
a_1 = value;
}
}
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}

public class A {
Container container;

public A (Container c)
{
container = c;
}

/*all methods of class A interact with container.A_1 ONLY*/

}

The other lettered classes follow the same format.
When Pex tests the Container class it will more than likely get 100% test coverage.
When Pex tests the lettered classes, however, it will not get 100% code coverage. The test coverage report includes coverage of the Container class, which does not require 100% coverage to test the lettered classes. The classes could arguably be written so that they are more easily testable; however, I did not write this code. I actually observed code similar to this in a real application. The lettered classes get 100% block coverage themselves but overall block coverage is never 100%.