How to use F# to unit test C# logic [closed] - unit-testing

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
Closed 7 years ago.
This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered.
We don’t allow questions seeking recommendations for books, tools, software libraries, and more. You can edit the question so it can be answered with facts and citations.
Improve this question
I am learning F# on my own and am trying to sneak some F# into the workplace.
As a result, I would like to write unit tests in F# to test C# logic.
Can anyone provide me a simple example of an F# unit test targeting a C# method and verifying a C# property as a result of exercising that method?
UPDATE:
Here's an example. When a value is provided for first and last name, how do we unit test (in F#) that GetFullName returns first and last name?
namespace MVVMExample
{
public class ViewModel : INotifyPropertyChanged
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set
{
_firstName = value;
RaisePropertyChanged("FirstName");
}
}
private string _lastName;
public string LastName
{
get { return _lastName; }
set
{
_lastName = value;
RaisePropertyChanged("LastName");
}
}
public string GetFullName()
{
return string.Format("{0} {1}", FirstName, LastName);
}
protected void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
}

Answer 1

So a very simple test for this ViewModel using NUnit could look like this:
testing GetFullName
here is a possible test for this function:
[<Test>]
member __.``GetFullName = "Jon Doe" if FirstName = "Jon" and LastName = "Doh"``() =
let vm = ViewModel()
vm.FirstName <- "Jon"
vm.LastName <- "Doe"
Assert.AreEqual("Jon Doe", vm.GetFullName())
testing PropertyChanged
[<TestFixture>]
type ``ViewModel Unit Tests``() =
[<Test>]
member __.``a PropertyChanged event should be raised if the FirstName was changed``() =
let vm = ViewModel()
let mutable lastChangedProperty = ""
vm.PropertyChanged.Add (fun e -> lastChangedProperty <- e.PropertyName)
vm.FirstName <- "Tom"
Assert.AreEqual("FirstName", lastChangedProperty)
Of course this is not really functional but I think it should be reasonable clear for the given problem.
as you can see it's basically the same you would expect from a C# test - the only F# feature I used are the function/class names in ``...`` which makes the output in your test-runner look nicer:
Code Walkthrough
the [TestFixture] class Test {...} just translates into [<TestFixture>] type Test() = ...
a [Test] method is just [<Test>] member this.MyTestFunction() = ... (this only if you need it - as you can see I did not so I used the idiomatic I-don't-care __ placeholder - see in F# you can name your this-reference any way you want - and you have to do it on each class-member.
as I want to change the lastChangedProperty string if the event is fired I declared it mutable (so you can use the assign operator <-)
to add an event-handler you can just use the .Addfunction on the event
(fun e -> ..) is an lambda - in C# this would be e => ...
disclaimer
of course if you want to use this viewmodel in say a WPF application you should make sure to dispatch to the UI-Thread, etc. which would make the test more nasty but for your example a simple red-green cycle should work ;)
I hope this helps you out (but of course it does not really show the advantages of F# as the test here is ugly side-effecty)