Added MessageTemplateParameter IsValidTemplateTest unit test

[304NotModified]

see #3181

todo:

• rebase/skip after merge Added MessageTemplateParametersTests (IsPositionalTest, IndexerTest, EnumeratorTest) #3291

@snakefoot

got some interesting results here:

With an empty list as object[] parameters , is always says IsValidTemplate=true - independent of the message-template. Is this expected? It this for performance reasons?

---

This change is 

[snakefoot]

@304NotModified With an empty list as object[] parameters , is always says IsValidTemplate=true - independent of the message-template. Is this expected? It this for performance reasons?

Have no special opinion about MessageTemplateParameters it was created for the Seq-target that wanted access to the internal parser engine of NLog (To perform special transformation for parameters prefixed with @)

By default NLog will ignore message-template when no parameters are provided. This is used by many that just writes raw Json without parameters. Whether there should be any correlation between the behavior of MessageTemplateParameters and the default parser/renderer behavior of NLog that I don't know.

Your own special fix with GetHoleValueSafe should probably also handle isValidTemplate :)

Any changes you make to MessageTemplateParameters should just be validated against the behavior of the Seq-Target.

[304NotModified]

related: #2339

[304NotModified]

closing for now, tracked here: #3375