Condition coverage on switch statement

Question

When I run coverage on my code below:

  private static String mapMyVal(String val) {
    switch (val) {
      case "foo":
        return "FOO_FOO";
      case "bar":
        return "BARR";
      default:
        throw new InvalidArgumentException();
    }
  }

I see "8 out of 10 conditions covered" when I run my unit tests on this with coverage. However I see all three lines being covered inside the statement.

Since there are no other conditions than "foo", "bar" and everything else, what are those missing two conditions?

Tim Biegeleisen · Accepted Answer · 2020-01-30T16:50:26.767

3

I see one possible case not covered. The input val might be null. In that case, your switch statement would throw a NullPointerException. To remedy this, you could add null check to the start of the method.

private static String mapMyVal(String val) {
    switch (val) {
        case "foo":
            return "FOO_FOO";
        case "bar":
            return "BARR";
        default:
            throw new InvalidArgumentException();
    }
}

edited Jan 30 '20 at 16:50

answered Jan 30 '20 at 16:46

Tim Biegeleisen

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@Nexevis You're right, and I retract what I wrote initially. But the `null` input edge case should be a concern. – Tim Biegeleisen Jan 30 '20 at 16:50
Good point. In my use case I am handling it before calling this method though e.g. null values never reach the method. Should coverage still consider `null` as a possible value? – Layman Jan 30 '20 at 16:52

score 1 · Answer 2 · answered Jan 30 '20 at 16:51

1

There was already someone asking nearly the same question. Overall it turned out that going for 100% of unittest for a switch-case might be pure luck because of the way that java is handling the switch-case. See here eclemma branch coverage for switch: 7 of 19 missed

answered Jan 30 '20 at 16:51

funky

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But those answers are from 2015. Surely issues with bytecode inspection that are described there were addressed over the last four years? – M. Prokhorov Jan 30 '20 at 17:02
Actually there is an blogentry in the web from the 14 Jan 2019 in which my linked answer is used as a resource. The author gets the same problem/result as the one I mentioned. – funky Jan 30 '20 at 17:12

Condition coverage on switch statement

2 Answers2