Example FAKE script to run all test at once

build.fsx

let artifactsDir = "./.ci/artifacts/"

/// modified versions of buildMSTestArgs wich adds testcontainer arguments for multiple assembiles https://github.com/fsharp/FAKE/blob/master/src/app/FakeLib/UnitTest/MSTest.fs
let buildMSTestArgs2 parameters (assemblies : string seq) = 

    // https://msdn.microsoft.com/de-de/library/ms182489.aspx#detail
    let detail_errormessage = "errormessage"
    let detail_errorstacktrace = "errorstacktrace"
    let detail_duration = "duration"
    
    // TODO: assemblies should be quoted each
    let testcontainers = assemblies |> separated " /testcontainer:"
    let testResultsFile = 
        if parameters.ResultsDir <> null && parameters.ResultsDir.EndsWith(".trx", StringComparison.OrdinalIgnoreCase) = false then 
            sprintf @"%s\%s.trx" parameters.ResultsDir (DateTime.Now.ToString("yyyyMMdd-HHmmss.ff"))
        else
            DeleteFile parameters.ResultsDir // delete file if exist 
            parameters.ResultsDir
    new System.Text.StringBuilder()
    |> appendWithoutQuotesIfNotNull testcontainers "/testcontainer:"
    |> appendIfNotNull parameters.Category "/category:"
    |> appendIfNotNull parameters.TestMetadataPath "/testmetadata:"
    |> appendIfNotNull parameters.TestSettingsPath "/testsettings:"
    |> appendIfNotNull testResultsFile "/resultsfile:"
    |> appendIfTrue parameters.NoIsolation "/noisolation"
    |> appendIfNotNull detail_errormessage "/detail:"
    |> appendIfNotNull detail_errorstacktrace "/detail:"
    |> appendIfNotNull detail_duration "/detail:"
    |> toText
    
/// modified versions of MSTest wich executes all tests at once https://github.com/fsharp/FAKE/blob/master/src/app/FakeLib/UnitTest/MSTest.fs
let MSTest2 (setParams : MSTestParams -> MSTestParams) (assemblies : string seq) = 

    let details = assemblies |> separated ", "
    traceStartTask "MSTest" details
    let parameters = MSTestDefaults |> setParams
    let assemblies = assemblies |> Seq.toArray
    if Array.isEmpty assemblies then failwith "MSTest: cannot run tests (the assembly list is empty)."
    let failIfError assembly exitCode = 
        if exitCode > 0 && parameters.ErrorLevel <> ErrorLevel.DontFailBuild then 
            let message = sprintf "%sMSTest test run failed for %s" Environment.NewLine assembly
            traceError message
            failwith message

    let args = buildMSTestArgs2 parameters assemblies
    ExecProcess (fun info -> 
        info.FileName <- parameters.ToolPath
        info.WorkingDirectory <- parameters.WorkingDir
        info.Arguments <- args) parameters.TimeOut
    |> failIfError "Test failed"
    traceEndTask "MSTest" details

Target "Test" (fun _ ->

    trace "Test..."

    !! "Tests/**/bin/**/*.Tests.dll"
    |> MSTest2 (fun p ->
        { p with
            Category = "!excel"
            ResultsDir = artifactsDir + "TestResults.trx"
            ErrorLevel = ErrorLevel.Error
            TestSettingsPath = testSettingsPath
            NoIsolation = false
            TimeOut = TimeSpan.FromMinutes 15.
        })
)