Use string.Contains() with switch()

Correct final syntax for [Mr. C]s answer.

With the release of VS2017RC and its C#7 support it works this way:

switch(message)
{
    case string a when a.Contains("test2"): return "no";
    case string b when b.Contains("test"): return "yes";
}

You should take care of the case ordering as the first match will be picked. That's why "test2" is placed prior to test.

Nope, switch statement requires compile time constants. The statement message.Contains("test") can evaluate true or false depending on the message so it is not a constant thus cannot be used as a 'case' for switch statement.