open NUnit.Framework - the namespace or module is not defined. Referencing in F#

Question

I am using VS2013 Professional , F# , C# and Nunit . It is worth noting that this is my first attempt with F# so question is most likely stupid and solution is obvious.

What I am trying to do is implement test cases using NUnit and use TestCaseSource attribute with TestCaseData .

Test:

namespace Legal.Tests.Helpers
open System
open System.Collections.Generic
open System.Linq
open System.Text
open System.Threading.Tasks
open NUnit.Framework
open Legal.Website.Infrastructure

type FTest() = 
    [<TestFixture>]
    [<TestCaseSource("FTestData")>]
    let ConcatTest(text : string, expected : string) =
    [<Test>]
        let actual = Saga.Services.Legal.Website.Infrastructure.FunctionModule.TestFunction text
        Assert.AreEqual expected actual
    let FTestData : seq<TestCaseData> = [ new TestCaseData (text = "x", expected = "Item1xItem2" ); new TestCaseData (text = "y", expected = "Item1yItem2" ) ] 

Function tested:

namespace Legal.Website.Infrastructure

open System
open System.Collections.Generic
open System.Linq
open System.Web

type Test(text2 : string) = 
  member this.Text = "Item1"
  member this.Text2 = text2

module functions = 
    let TestFunction (text : string) =
        let test = new Test (text2 = "Item2")
        String.Concat [test.Text; text; test.Text2]

One thing worth noting - I have created F# test file and file with function by renaming .cs file to .fs .

Problem: when I try to open any library that is not System (in this case Nuget package NUnit.Framework and Referenced project Legal.Website.Infrastructure ) I get error: the namespace or module is not defined both are referenced in Test Project and .cs tests in same directory run fine.

Answer 1

My question is stupid.

.fs files cannot be added to C# project like for example .vb files. To do this properly one needs to add F# project to solution, see screenshot below.

Implementation:

module Implementation

let Concat(text:string) = 
    "root"+ text

Test:

module Test
open NUnit.Framework

[<TestFixture>]
type Test() = 
    member this.ConcatinationTestData() = 
        [new TestCaseData("roottext","text"); new TestCaseData("root","")]
    [<Test>]
    [<TestCaseSource("ConcatinationTestData")>]
    static member ConcatinationTest(expected:string, text:string) =
       Assert.AreEqual(expected,Implementation.Concat(text))
       |> ignore

Debug -> Attach to process -> nunit-agent.exe

Result: