throwWithRegexMessage

I find myself using regex to match dynamic errors, could this be added?

let throwWithRegexMessage (m:string) (t:System.Type) = CustomMatcher<obj>(sprintf "%s \"%s\"" (string t) m,
                                                                    fun f -> match f with
                                                                             | :? (unit -> unit) as testFunc ->
                                                                                 try
                                                                                   testFunc()
                                                                                   false
                                                                                 with
                                                                                 | ex -> ex.GetType() = t && Regex.IsMatch (ex.Message, m)
                                                                             | _ -> false )

(fun () -> AsyncWrite2 (streamName) (int64(EventStore.ClientAPI.ExpectedVersion.Any)) (event)
               |> Async.RunSynchronously
               |> ignore)
    |> should (throwWithRegexMessage @"EventStoreConnection 'ES-.{36}' is not active.") typeof<System.AggregateException>

Maybe there could be a better message I can make the PR if worth including.

[CaptnCodr]

Diffract can show you a diff of your F# types etc., see: https://github.com/d-edge/Diffract

[sergey-tihon]

I am not aware about such diffs for .net test frameworks. I believe it cannot be added to DSL library (like FsUnit), It should be supposrted by framework (xUnit, NUnit, MSUnit) and runner (console runner) that will provide colorful output.

AFAIK, Expecto support string diff (but for a git-like diff for objects) https://github.com/haf/expecto/releases/tag/v2.2.0