Unit testing code coverage – do you have 100% coverage?

Question

No for several reasons :

It is really expensive to reach the 100% coverage, compared to the 90% or 95% for a benefit that is not obvious.
Even with 100% of coverage, your code is not perfect. Take a look at this method (in fact it depends on which type of coverage you are talking about – branch coverage, line coverage…):

public static String foo(boolean someCondition) {
    String bar = null;
    if (someCondition) {
        bar = "blabla";
    }
    return bar.trim();
}

and the unit test:

assertEquals("blabla", foo(true));

The test will succeed, and your code coverage is 100%. However, if you add another test:

assertEquals("blabla", foo(false));

then you will get a NullPointerException. And as you were at 100% with the first test, you would have not necessarily write the second one!

Generally, I consider that the critical code must be covered at almost 100%, while the other code can be covered at 85-90%

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