which is not unexpected as it is a handler for an Enum which should not be set to any value that is not part of the allowed values. Looking at the branch coverage report we have the following results (the switch instruction we are interested in is at IL offset 8.
Now the first path (0) is unvisited, but we knew that, so the next unvisited branch is #14 and the next is #17; luckily for us the enum in question that is used by the switch instruction is well defined.
And as such we can thus deduce that the method is never called during testing with the values Symbol and TimeStamp but the code that they would call is covered; in fact we can see from the code that both these enum values are part of the switch/case statement and are part of fall-throughs. So again we see how branch coverage helps identify 'potential' issues and test candidates.