HOW LONG WILL IT TAKE YOU?

@RBARTELINK

DUBLIN ALT.NET

24 OCTOBER, 2013

Testing . NET systems using F#

The test pyramid

It’s not easy to achieve a good balance in a set of tests Too much AT -> slow + doesn’t drive implementation

properly Too much UT -> Not meeting Living Documentation

aimOne size won’t fit all

http://martinfowler.com/bliki/TestPyramid.html (originated by Mike Cohn)

ATDD workflow

http://www.infoq.com/articles/atdd-from-the-trenches

Why?

You need to express high and low level testsMbUnit, Sub/N/M/Spec are single paradigm3 year old tests are uglier than 3yo

production codeTest code is just different to production codeLearn a language a yearF# has been in VS since 2009One of F#’s many paradigms is to be a better

C#

What can I use

Everything (yes, everything) you know NUnit, MSpec, SpecFlow FluentAssertions, RhinoMocks, FakeItEasy, NSubstitute

Things you’re already using xUnit.net, LINQ, Moq

Modern Libs AutoFixture, AutoFixture.xUnit, AutoFixture.AutoMoq Foq, AutoFixture.AutoFoq TickSpec

Gherkin

Feature files (Gherkin) Feature: Addition In order to avoid silly mistakes As a math idiot I want to be told the sum of two numbers

Scenario: Add two numbers When I add 2 and 2 Then I should see 4

TickSpec

TickFacts [<TickFact>] let AdditionFeature () = EmbeddedResourceFeatures.ScenariosFrom “Addition"

Step Definitions (TickSpec with unquote)module CalculatorSteps = [<When>] ``I add (.*) and (.*)`` x y = result <- Calculator() |> enter x |> plus |> enter y |> compute [<Then>] ``I should see (.*)`` expected = test <@ expected = result @>

Gherkin Backgrounds and Outlines

Feature: Addition

Background: Given I switch my calculator to fancy mode

Scenario Outline: The Hard Stuff When I add <First> and <Second> Then I should see <Total>

Examples: |First|Second|Total| |1 |1 |2 | |9 |-1 |8 |

Unit Testing

Tick methods (xUnit/NUnit with unquote)module CalculatorFacts = [<Fact>] let ``Adding two small ints works`` () = let result = Calculator() |> enter 2 |> plus |> enter 2 |> compute

test <@ 2+2 = result @>

Mocking DSLs (Foq)Mock<IList<char>>.With(fun x -> <@ x.Count --> 2 x.Item(0) --> '0' x.Item(1) --> '1' x.Contains( any() ) --> true x.RemoveAt( 2) ==> System.ArgumentOutOfRangeException() @>)

Low Level Stuff

Type inference (for real)

any() It.IsAny<DateTime>()

mock() Mock.Of<T>

Tuples let tuple = key,valuelet _,value = tuple

var tuple = Tuple.Create( key, value)var value = tuple.Item2

Lambdas let gen a b = CreateSut a b |> Filllet gen = CreateSut >> Fill

var gen = (int a, int b) => CreateSut( a, b).Fill()

Object Expressions

let time = { new ITime with member mock.GetHour() = 15}

class FakeTime15 {int GetHour() { return 15;}}var time = new FakeTime15()

Custom ops expected =? Actual // From unquote Asset.Equal( expected, actual)

Quotations test <@ expected = result |> String.Concat “,” @>

Assert.That( expected, Is.EqualTo( String.Concat( “,”, result)));

let list = Mock<IList> .Method(fun x -> <@ x.Contains @>) .Returns( true)

var mock = new Mock<IList>();mock.Setup( x=> x .Contains( It.IsAny<object>()) .Returns( true)var list = mock.Object;

The bad points

Need to install FSC on CI server (2 clicks or 11 MB MSI or put FSC in tools dir Just Works)

You can’t mix F# and C# in a single projectF12 from F# to/from C# doesn’t work (but

built in Ctrl-, and F12 within files is fine)No refactoring support of consequence (but

not as important as you think)C# starts to grate a little more every day (as

does “in F# you can just…”)

Books

Growing Object Oriented Software, Guided by Tests (Freeman, Pryce)

Specification By Example (Adzic)The RSpec book (Chelimsky et al)Expert F# 3 (Syme)Real World Functional Programming in F#

and C# (Petricek, Skeet)

Resources

F# @ptrelford http://trelford.com/blog and samples SO F# tag Google @tomaspetricek http://tomasp.net/blog/ Don’t forget MSDN

ATDD GOOS @ploeh Outside In Test Driven Development

http://pluralsight.com/training/Courses/TableOfContents/outside-in-tdd