Friday, 20 June 2014

Unit Testing Is Dead

Haskell logo (Wikipedia)
Don't Bury The Lede!

Fair enough. Here's the power point takeaway:
  • The future present is multicore!
  • Only functional programming languages (Haskell and Erlang for the purist, but also Scala, Ocaml, F#) can scale adequately to cope with this future present.
  • Functional software design eschews mutable state, being purely procedural and "static".
  • Objects and interfaces (and O-O generally) are obsolete.
  • Unit testing, as we used to know it, is dead! Yeah! And TDD/BDD too! Yeah!
  • But we still have to support our legacy O-O systems with unit tests...
  • Here's how to do that without jettisoning statics.

LINQ The Hero

The introduction of Language-INtegrated Query (LINQ) into the C# language, with C# 3.0 in November 2007, headlined an impressive list of new features. But in truth, there was only one major, new feature delivered in that compiler release. Virtually everything else, with the possible exception of Automatic Properties, was introduced simply to underpin and enable the great LINQ:
  • Anonymous Types
  • Local Variable Type Inference
  • Object and Collection Initializers
  • Lambda Expressions and Trees
  • Extension and Partial Methods
Some examples of these dependencies:
  1. Local Variable Type Inference is essential when returning values of an Anonymous Type from a query.
  2. Lambda Expressions are required to enable the writing of sufficiently general SQL WHERE clause predicates.
  3. Extension Methods provide the backbone of the "fluent" (method chaining) syntax, upon which the Query Comprehension (using SQL-like keywords) is just compiler syntactic sugar.
Naturally, most of these supporting features have found immediate application in multiple other areas. Extension Methods in particular have spawned an entire vocabulary of Fluent APIs (of which my favourite has always been Bertrand Le Roy's FluentPath). These are popular with developers and library code consumers alike, being in the words of TechPro's Khalid Abuhakmeha fun and discoverable way to allow fellow developers to access functionality.

Villain Of The Piece

But with great power comes, as they say, great heatsinks. And coolest in their response to the proliferation of these extensions, implemented as they are throughout C# using static methods, are the unit test evangelistas. Their point is simple and well-made:
  • Unit testing involves rewiring your dependencies using mocks or "friendlies" which replace those real dependencies for test purposes.
  • Static methods lead to an essentially procedural programming environment, with code and data separated, and without clear objects or interfaces available to be swapped out and substituted.
So much the worse for static methods, they say. To which I rejoin, so much the worse for your unit testing framework! Not all such tools have intractable bother with statics.


Microsoft's Pex and Moles VS2010 power tools, and their VS2012 replacement Fakes Framework (via Shims, though not Stubs), can handle statics reasonably well.


The Typemock Isolator can control the behavior of static methods, just like any other method:
  .WhenCalled(() => MessageBox.Show("ignored arg"))
So, your test might look like this:
public void TestStaticClass()
  Isolate.WhenCalled(() => UserNotification.SomeMethod()).WillReturn(5);
  Assert.AreEqual(5, UserNotification.SomeMethod());
Telerik JustMock

JustMock provides for unrestricted mocking of dependent objects, including non-virtual methods, sealed classes, static methods and classes, as well as non-public members and types. Mocking of properties like get calls, indexers and set operations is also supported. JustMock also supports mocking of all classes and methods included in the MSCorlib assembly.

Don't Meddle With The IL?

Some of these solutions engender suspicion because of their under-the-hood behaviour. Specifically, there is concern that anything rewriting the actual Intermediate Language (IL) generated by the compiler, for consumption by the jitter, must result in something other than the official written code being tested. But this is an unjustified worry for several reasons.
  • By its very nature, IL is not the code that's finally executed on the end user's processor. What does the jitter do, but transform that IL into something entirely new?
  • Several .NET components cause new IL to be generated at run time. For example, Regex patterns which are not precompiled cause their own custom assemblies to be generated each time they are evaluated.
  • Visual Studio design mode is the biggest IL simulator of them all. Just ask yourself, how does it run the constructor for your new user control in design mode, when you haven't even finished typing it in yet, never mind compiling it?!
In short, these Shimmying frameworks are thoughtfully designed and quite serviceable, and aren't doing anything outlandish that you're not already relying on to a great extent.

Further Reading

Statics and Testability

Miško Hevery, Russ Ruffer and Jonathan Wolter's Guide to Writing Testable Code (November 2008) lists warning signs related to the four most popular flaws in O-O Design. (Google)

Miško Hevery, Static Methods are Death to Testability (December 2008) goes into more detail and answers commentators' concerns with the previous document.

Introductions to Functional Programming

Learn You a Haskell for Great Good!

This is the world's best tutorial introduction to the world's best programming language.

Learn You Some Erlang for Great Good!

This is the world's best tutorial introduction to the world's second best programming language.