Unit Testing with F#

Sugak Alexandr

Unit Testing

Functional design is testable by its

nature

Pure function – always returns the same value given the same input

and has no side-effects

Isolated function – a function which knows nothing about the state of

the external world, except information passed via its arguments

A pure function is isolated

Assertion, C# way (MSTest)

Structural Equality

F# has Structural Equality for:

• Records

• Discriminated Unions

• Arrays

• Lists

Assertion, F# way (Unquote)

Unquote uses F# quoted expressions to express assertions

and produce detailed error messages

Isolation, C# way

• Moq

• Rhino Mocks

• Typemock Isolator

• NMock

• NUnit.Mocks

• Microsoft Fakes / Moles

• NSubstitute

• FakeItEasy

Isolation, C# example

Isolation, C# example

Isolation, C# example

Isolation, F# way

Unit Testing with F#

• Less mocks

(more stubs)

• Simpler assertions

(unquote)

• No test induced damage

(functions as interfaces)

DEMO

Links

• Unquote - https://code.google.com/p/unquote/

• Railway Oriented Programming -

http://fsharpforfunandprofit.com/posts/recipe-part2/

• Mark Seeman’s blog - http://blog.ploeh.dk/

• Mark Seeman’s Pluralsight courses -

http://www.pluralsight.com/author/mark-seemann

(highly recommended!)