mountebank mocks with F#

mountebank.fs

namespace Mountebank

// PM> Install-Package FSharp.Data

open FSharp.Data
open System

module Imposter = 
    let Create protocol host port =
        Http.Request(
            "http://" + host + ":2525/imposters/",
            headers = [ 
                "Content-Type", HttpContentTypes.Json; 
                "Accept", HttpContentTypes.Json ],
            httpMethod = "POST",
            body = 
                TextRequest 
                    (sprintf @"{ ""port"": %i, ""protocol"": ""%s"" }" 
                        port protocol))

    let GetCapturedRequests (spy : HttpResponse) = 
        let getRequests jsonValue = 
            match jsonValue with
            | FSharp.Data.Record properties ->
                match properties with
                | [| protocol; port; requests; stubs; _links; |] ->
                    match snd requests with
                    | FSharp.Data.Array elements ->
                        match elements |> Seq.toList with
                        | head :: tail -> Some(elements)
                        | [] -> None
                    | _ -> None
                | _ -> None
            | _ -> None
        let response = 
            Http.Request(
                spy.Headers.Item "Location",
                headers = [ 
                    "Content-Type", HttpContentTypes.Json; 
                    "Accept", HttpContentTypes.Json ],
                httpMethod = "DELETE")
        match response.Body with
        | Text json -> 
            JsonValue.Parse json 
            |> getRequests
        | _ -> None
        
module SmtpSpy = 
    let GetCapturedRequest imposter propertyName =
        let filter properties propertyName = 
            match properties with
            | [| _; _; _; _; _; _; _; _; _; _; _; _; _; _ |] -> 
                (properties
                |> Array.filter (fun (name, _) -> name = propertyName)
                |> Seq.head
                |> snd).ToString().TrimStart('"').TrimEnd('"')
                |> Some
            | _ -> None
        match Imposter.GetCapturedRequests imposter with
        | Some actual -> 
            match actual |> Seq.head with
            | FSharp.Data.Record properties -> filter properties propertyName
            | _ -> None
        | _  -> None

Scenarios.fs

module Mountebank.Scenarios

// PM> Install-Package xunit
// PM> Install-Package Unquote

open System
open System.Net.Mail
open Xunit

let verify = Swensen.Unquote.Assertions.test

[<Fact>]
let SendMailTransmitsCorrectSubject () =
    let expectedSubject = "Thank you for your order!"
    let mountebankHost = "192.168.1.4"
    let imposterPort = 4547
    let spy = Imposter.Create "smtp" mountebankHost imposterPort
    
    (new SmtpClient(mountebankHost, imposterPort)).Send(
        new MailMessage(
            "customer-service@company.com", 
            "customer@domain.com", 
            expectedSubject, 
            "Hello Customer, Thank you for your order from company.com."))
    
    verify <@
            match SmtpSpy.GetCapturedRequest spy "subject" with
            | Some actual -> expectedSubject = actual
            | None        -> 
                raise <| InvalidOperationException(
                    "No property named 'subject' found in captured requests.") @>
                    
[<Fact>]
let SendMailTransmitsCorrectNumberOfSmtpRequests () =
    let expectedNumberOfRequests = 1
    let mountebankHost = "192.168.1.4"
    let imposterPort = 4546
    let spy = Imposter.Create "smtp" mountebankHost imposterPort
        
    (new SmtpClient(mountebankHost, imposterPort)).Send(
        new MailMessage(
            "customer-service@company.com", 
            "customer@domain.com", 
            "Thank you for your order!", 
            "Hello Customer, Thank you for your order from company.com."))
    
    verify <@
            match Imposter.GetCapturedRequests spy with
            | Some actual -> expectedNumberOfRequests = (actual |> Seq.length)
            | None -> 
                raise <| InvalidOperationException(
                    sprintf "Expected %i calls but received none." 
                        expectedNumberOfRequests) @>