Category Archives: Model-Driven Architecture

My Case for DTO’s

In many of my posts about Grails and Flex integration, I take for granted that I use Data Transfer Objects to transfer data between my Grails backend and my Flex frontend. Put simply, Data Transfer Object are pure data containing classes different from the domain entity classes used to store data in the backend. I take it for granted because I’m deeply convinced that it’s the best way to do things and so far, experience has never proved me wrong. But I often get this question in comments or by mail (this is for you Martijn): why bother create an entirely separate class structure and copy data from entities to DTO’s and back instead of just using entities?

I’ve expressed my arguments a couple of times across various posts but I thought it would be nice to sum things up in here for future reference.

Where does it come from?

When I first started to work on enterprise applications and ORM-based architectures, it was with a Model-Driven Architecture framework called AndroMDA. AndroMDA was absolutely key in helping me getting started with Spring and Hibernate and I was especially inspired by one paragraph in their “getting started” tutorial, which I quote here:

Data Propagation Between Layers

In addition to the concepts discussed previously, it is important to understand how data propagates between various layers of an application. Follow along the diagram above as we start from the bottom up.

As you know, relational databases store data as records in tables. The data access layer fetches these records from the database and transforms them into objects that represent entities in the business domain. Hence, these objects are called business entities.

Going one level up, the data access layer passes the entities to the business layer where business logic is performed.

The last thing to discuss is the propagation of data between the business layer and the presentation layer, for which there are two schools of thought. Some people recommend that the presentation layer should be given direct access to business entities. Others recommend just the opposite, i.e. business entities should be off limits to the presentation layer and that the business layer should package necessary information into so-called “value objects” and transfer these value objects to the presentation layer. Let’s look at the pros and cons of these two approaches.

The first approach (entities only, no value objects) is simpler to implement. You do not have to create value objects or write any code to transfer information between entities and value objects. In fact, this approach will probably work well for simple, small applications where the the presentation layer and the service layer run on the same machine. However, this approach does not scale well for larger and more complex applications. Here’s why:

  • Business logic is no longer contained in the business layer. It is tempting to freely manipulate entities in the presentation layer and thus spread the business logic in multiple places — definitely a maintenance nightmare. In case there are multiple front-ends to a service, business logic must be duplicated in all these front-ends. In addition, there is no protection against the presentation layer corrupting the entities – intentionally or unintentionally!
  • When the presentation layer is running on a different machine (as in the case of a rich client), it is very inefficient to serialize a whole network of entities and send it across the wire. Take the example of showing a list of orders to the user. In this scenario, you really don’t need to transfer the gory details of every order to the client application. All you need is perhaps the order number, order date and total amount for each order. If the user later wishes to see the details of a specific order, you can always serialize that entire order and send it across the wire.
  • Passing real entities to the client may pose a security risk. Do you want the client application to have access to the salary information inside the Employee object or your profit margins inside the Order object?

Value objects provide a solution for all these problems. Yes, they require you to write a little extra code; but in return, you get a bullet-proof business layer that communicates efficiently with the presentation layer. You can think of a value object as a controlled view into one or more entities relevant to your client application. Note that AndroMDA provides some basic support for translation between entities and value objects, as you will see in the tutorial.

Because of this paragraph, I started writing all my business services with only data transfer objects (what they call “value objects”) as input and output. And it worked great. Yes it did require a little bit of coding, especially as I had not discovered Groovy yet, but it was worth the time, for all the following reasons.

The conceptual argument: presentation/storage impedance mismatch

Object-relational mapping is what Joel Spolsky calls a “Leaky Abstraction“. It’s supposed to hide away the fact that your business entities are in fact stored in a relational database, but it forces you to do all sorts of choices because of that very fact. You have to save data in a certain order in order not to break certain integrity constraints, certain patterns are to be avoided for better query performance, and so on and so forth. So whether we like it or not, our domain model is filled with “relational choices”.

Now the way data is presented involves a whole different set of constraints. Data is very often presented in a master/detail format, which means you first display a list of items, with only a few fields for each item, and possible some of those fields are calculated based on data that is stored in the database. For example, you may store a country code in your database, but you will display the full country name in the list. And then when the user double-clicks an item, he can see all the fields for that item. This pattern is totally different from how you actually store the data.

So even though some of the fields in your DTO’s will be mere copies of their counterparts in the entity, that’s only true for simple String-typed fields. As soon as you start dealing with dates, formatted floats or enum codes, there is some transformation involved, and doing all that transformation on the client-side is not always the best option, especially when you have several user interfaces on top of your backend (a Flex app and an iPhone app for example), in which case you’re better off doing most of these transformations on the server.

In anyway, if you change the way you store data, it should not influence too much the way you present the same data, and vice-versa. This decoupling is very important for me.

The bandwidth argument: load just the data you need

In the master/data use case, when you display the list of items, you just need a subset of the fields from your entities, not all of them. And even though you’re using Hibernate on the backend with lazy-loading enabled, fields are still initialized and transferred over the wire. So if you use entity classes for data transfer, you will end up transferring a whole bunch of data that may never be used. Now it might not be very important for hundreds of records, but it starts being a problem with thousands of records, especially when there is some parsing involved. The less data you transfer the better.

The security argument: show only the data you want to show

Let’s say you’re displaying a list of users, and in the database, each user has a credit card number. Now of course when you display a list of users, you might not want everyone to see the list of credit card numbers. You might want to expose this data only in detail view for certain users with certain privileges. DTO’s allow you to tailor your API to expose just the data you need.

The error-prone argument: argh! Yet another LazyInitializationException!

Of course there are associations between your business entities, and by default, those associations are lazy-loaded, which means they are not initialized until you actually query them. So if you just load a bunch of instances from your entity manager and send them over to your client, the client might end up with null collections. Now of course you can always pay attention, or use some tricks to initialize associations up to a certain level before you send your data, but this process is not automatic and it’s very error-prone. As for using things like dpHibernate, I think it just adds too much complexity and uncontrolled server requests.

The laziness argument: Come on! It’s not that hard!

I think that most of the time, the real reason why people don’t want to use DTO’s is because they’re lazy. Creating new classes, maintaining code that does “almost” the same as existing code, adding some code to service implementation to copy data back and forth, all of that takes time and effort. But laziness has never been a good reason for ditching a design pattern altogether. Yes, sometimes, best practices force us to do more stuff for the sake of maintainability and robustness of our code, and for me the solution is certainly not to shortcut the whole practice, but just to find the best tools to minimize the added work. With its property support and collection closures, Groovy makes both creating, maintaining and feeding DTO’s as simple and fast as it can be. AndroMDA had converters. There are even some DTO-mapping frameworks like Dozer to help you. No excuse for laziness.

For me, all the reasons above largely overcome the added work to maintain a parallel DTO structure.

Now of course, this is a very opinionated topic and you will probably have a different view. So all your comments are welcome as long as they remain constructive and argumented.

Text, Expressivity and Culture-Oriented Programming

Following up on my reflexion about what could software development look like a few years or decades from now, there is this big problem that has been bugging me for years now and that I have never found the time to really tackle: expressivity. In the same way as files appear to me as the biggest obstacle to collaboration, I think the main barrier in the way of expressivity is TEXT.

It’s hard to admit, but we’re still building software like cavemen. We don’t have spoken language, just a bunch of noises, we don’t conceptualize much but we do communicate with a few gestures and more importantly some colored drawings on cave walls. The way I see it, we are not much more advanced than that, but it’s normal, software is still relatively young as a discipline and although it has already changed our lives, we have to imagine that it’s just the beginning. And the good news is that we are headed in the right direction.

man

We started off with most elementary way of storing information and communicating with a machine: zeros and ones. Binary. It was too elementary, more like noises coming out of our mouths, so we started to group bits in octets corresponding to hardware instructions and characters. In fact, we added gestures to noises. Then we grouped instructions into statements and procedures, and we designed a way to translate those into the most elementary form of language that machines could understand. We started drawing on walls. But as procedures multiplied like crazy, we needed to conceptualize some more, talking about classes, objects, methods, properties, and so on. Spoken language was born. And with higher level concepts like services, components and multiple programming languages, we added written language. OK, the analogy is not that good, but you get my point: I’m convinced we’re still very early in the overall evolution of communication with machines, and although this evolution is somewhat slow and creates a lot of inertia, I believe that if we want computers to really expand our capabilities (note that I didn’t say “replace us”), we need to go further in abstraction levels.

So what’s next? Binary, assembly, procedural, object-oriented (yes, and functional, if you want), then what? Model-driven? I’ve tried that, it’s just replacing the constraints of text with the constraints of visual representations. It sure makes it easier to conceptualize, but at some point we’re still translating those visual models into text code, which we have to compile. The roundtrip is just too long. What about domain-specific languages? Well, I’m more into that right now. It looks like communicating is naturally based on languages, collections of concepts that relate with one another to describe what a software is and what it does. So focusing on making it easier to define new languages definitely goes in the right direction. That’s why it’s so linked with meta-programming: instead of statically defining layers upon layers of fixed concepts to describe systems with even higher level abstractions, let’s define the root concepts we will use to describe languages that will allow us to describe our systems. That’s why I’m so interested in Groovy at the moment for internal DSLs, although I prefer the more elegant idea of external DSLs and language workbenches, like Jetbrains MPS does.

All of this evolution makes me think of a video I saw recently, that tried to make String theory more accessible:

Let’s say binary is our dimension 0. Assembly is dimension 1: a line. Procedural programming is dimension 2: a plane. Object-Oriented Programming is then 3rd dimension: a volume. And it’s very hard for us to leave it, as it is our most natural way of seeing things. But that’s where I find this explanation of String theory particulary interesting (although not rigorous as some math geek friends of mine pointed out): there starts a cycle. Dimension 4 is a line again, formed by 2 different Object-Oriented Languages, like Java and C++ for example. Still there? Good! That’s where the fun starts: dimension 5 is a plane composed by all the parallel universes that are created by our own choices. Functional programming and OOP can be considered as forming such a plan. Now what if we could design a way to go directly from one of those paradigms to another one, to fold the plane in the 6th dimension: please welcome language-oriented (or meta-) programming! See the cycle? Now most of us are stuck in the 3rd dimension, and some of us are already experiencing the 6th dimension.

So there we are. Seventh dimension is the line joining the set of all possible timelines starting from our software big bang, which is the binary transistor, to another set of possible timelines, starting from another big bang. Quantum computing can be another option, but it’s a hardware one. What about software? Isn’t virtualization a way to forget about the physical hardware? And there we go 8th dimension: going from binary transistors to quantum computing is one line in the seventh dimension. Choosing to go to virtualization instead creates an branching line in the 8th dimension. Which means that if we want to create our ninth dimension, we need to fold the eighth in order to jump from quantum to virtual computing. And that’s where I locate what I call Culture-Oriented Programming. The third stage of the third 3-stage cycle. The final frontier? The next step? Hooooo… my head hurts.

But wait a second, I only talked about computing here. A virtual reality. What if dimension 10 was the line uniting computing with the real world in the purest possible way. Direct communication between human beings and computers. Who said “scary”?

PS: I didn’t intend this post to be so “theoretical”. I only thought with my keyboard and let my imagination go. But I’d love to know what you think about that crazy analogy? Do you think we are limited to 11 dimensions like in string theory?

PPS: That might be my geekiest post EVER!

2008 flashback

That’s it. Holidays are here, this year is almost over, time slows down for a few days so that we can look back, then enjoy and start again.

img_0076This post is probably not be of great use to anyone but me, but it’s a blog after all, sometimes I can use it as a personal journal too, like all those teenagers.

This year was actually very rich to me. I got to discover a few very interesting technologies, starting with OSGi and its ability to break up with big monolithic enterprise applications. And I really dived into Flex and how it can integrate with Java, which culminated in this tutorial, which was even republished on the Adobe Developer Connection. And finally, in my quest to discover better ways to develop applications, I came across Jetbrains MPS. And when I realized it was still far from being ready for prime time, I decided to keep it on my radar but focus on a more realistic alternative on a shorter term: Groovy/Grails. Now I’ve widened my technological scope beyond just JEE and AndroMDA, and I feel quite ready for the challenges ahead.

More importantly, this year will have been a great initiatic journey. Last year at about the same period, I decided I wanted to turn one of my ideas into a company, to create my own startup. The road was bumpy, my colleagues at Axen could feel it, friends who joined me on this journey could feel it too. I put a lot of things in question: my job, my ambitions, my strengths and weaknesses. And the project failed… so far! But they say there’s always hope at the end of the tunnel.

I had the idea, I had the skills, I had the will, time and energy, and yet there was this big barrier to entry, this thing that seems so important to everybody that nations and societies, people and governments are falling apart just because of it: money. I’ve always felt bad about money, like it was the poisonous blood flowing in the veins of an otherwise healthy man, eating him from the inside out, like something that is here to transport what makes us live, but that we’ve come to confuse for life itself. And it happened, crisis happened, the disease hit us all. We’re still far from the bottom since we still believe that the best cure against poisonous blood is more blood. But I don’t want to wait. My failed project and the recent course of events have made me realize something: THERE’S GOTTA BE A BETTER WAY!

2009 is full of promises. I have already started to understand many things about myself, about why I failed on this project, about how I live, how I can improve. I moved to a new place too, more comfortable, more like me. And now I have this new project, this game changer, this new way of thinking about how creative people can turn ideas into something real. 2009 is going to be fan… wait for it… tastic!

Talk Less, Do More

I’ve been a Java developer for almost 8 years now, I’ve used many frameworks and tools, Spring, Hibernate, EJB’s, Swing, etc. And a few years back, I started to look for a less verbose way to express concepts like business entities, services, workflows and so on. For some time, Model-Driven Architecture (MDA) has been the best answer I could find. But the learning curve and the difficulty to customize transformation patterns for specific setups, like a Flex front-end on a Spring back-end for example, have made me realize that this approach was somewhat limited by its UML foundation.

So I started looking for a better answer, and I thought I had found it with Language-Oriented Programming, the idea to decouple the structure, the syntax and the semantics of a language and ease the creation of Domain-Specific Languages in a very generic way. Unfortunately, as promising as it looks, it’s still in early stages of research and development and I needed a more immediate way to improve my productivity, my ability to do more with less words.

So I came back to something I had totally pushed aside till then: scripting languages. I’ve been “raised” with strongly and statically-typed languages since day 1 of my programming carrier: first Pascal, then Delphi, C++ and Java. And I always thought that scripting languages like PHP, and later Ruby were just tinkerer stuff for lazy hobbyist programmers, that didn’t take into account constraints like maintainability, robustness, readability, performance, etc. All those constraints I faced as a professional consultant. But a few weeks ago, I started to question my certainties and began wandering around PHP, Ruby, Python and others.

PHP, I’m using it at work on You And The World, it’s too hard to debug in a Flex/AMF setup and it’s really too permissive. As for Ruby, I like the ability to design DSLs but the syntax is definitely not intuitive enough for me. So now, I’m trying to learn more about Python, whose syntax seemed more familiar and maturity is reassuring. Everything seemed good until I read this single sentence in the documentation:

[…] classes in Python do not put an absolute barrier between definition and user, but rather rely on the politeness of the user not to “break into the definition.”

Come ooooon! Politeness of the user? You must be kidding right. In a corporate environment, when your code is likely to be reused and shared and refactored? I thought “hey, that’s probably just a provocative way to say that we Java developers tend to overdesign, and I know it’s true… so let’s read on…”. But unfortunately it proved to be much more than just a provocative sentence, since a few lines later:

In fact, nothing in Python makes it possible to enforce data hiding — it is all based upon convention.

OK. It took me a while to accept the argument that static typing can be too much of a cost in terms of verbosity compared to the poor protection it offers in terms of code correctness. But I said “OK, we’ll see how it looks when we come to real code”. But now they want me to forget about encapsulation too! What is the purpose of even writing a class then? What are you describing? A library of functions with a hidden first parameter? Is that it?

I mean, typing might be a unnecessary hurdle when writing unit test becomes much easier, but giving up on the behavior/state balance, the ability to describe what a class can do AND what it looks like, this is too much to ask.

So now what? Am I stuck between two extreme alternatives: either describe everything and waste energy doing it, or describe nothing a pray/ask for politeness?

And then I thought about LOP, and this interesting idea to decouple structure, syntax and semantics. After all, programming languages have entangled those three aspects for decades. And now both mainstream platforms (Java and .Net) are offering a variety of languages running on the same Virtual Machine. Isn’t that a first step in decoupling syntax on one side, structure and semantics on the other side?

Suddenly I’m starting to dream of a new syntax, far less verbose than the one of the Java programming language but with the same rigorous Object-Oriented structure, and the ability to run on all runtimes with different semantics…

What if the following Java code:

{code type=java}
public class TodoItem extends Item implements Synchronizable{
private String title;
public String getTitle(){return title;}
public void setTitle(String t){title=t;}

protected boolean done;

public TodoItem(String title){this.title=title;}

public void check(){done=true;}
}
{/code}

Could be rewritten like this:
{code}
+ class TodoItem > Item @ Synchronizable
– title
+ <-
return title
+ -> t
title = t

#done

init t
title = t;

+ check
done = true
{/code}

…or something similar ;o)

The key ideas being:

  • Keep all the key concepts of OOP: encapsulation, inheritance, polymorphism, composition
  • Remove static type declaration: I don’t care that my hammer has a wood or a steel handle, but I need to know it has a handle.
  • Replace long keywords by well-identified signs
  • Replace “{}” and “;” by indentation (Python-like)
  • Add simple property syntax (I love the way ActionScript does it)

In other words, I’m looking for a middle-path alternative between Java and Python, between waste and pray, between overdesign and politeness. Does anyone know of a language that offers that kind of compromise? Does anyone know if it has already been tested but has proven to be a dead-end for some reason?

The End of an Era, the Beginning of a New One

I’m a pure product of the Object-Oriented Programming generation. I’ve experimented several different paradigms when I was in engineering school, including formal programming in B, functional programming in OCaml, logical programming with PROLOG and Eclipse (the programming language, not the IDE). But when I started writing software in high school, it was with TurboPascal and then Delphi. And the main language I’ve been using during my studies was Java.

During all that time, I essentially worked on relatively simple problematics, and my end-of-study project was the first one where I started to look for better ways to handle a more complex environment, namely web applications and web services. The revelation came from AndroMDA, an Open-Source Model-Driven Architecture framework that has been my main specialty and domain of research during the past three years or so. As a professional IT consultant, I’ve used it and promoted it on at least 3 customer projects with rather great success.

But today, I think this time is over. I’ll move on to the next step, my next toy. And if you’ve read my previous entry about the limitations of OOP and its comments, you might guess what it is. I was looking for a better way to tackle today’s software issues and go further in my philosophical goal to make technology useful, and I found it. It’s called Language-Oriented Programming.

If you want to know more about it and wonder why I moved onto this so quickly, here are the articles that hit me as another revelation during the past couple of days:

Now I think I’ll have a much closer look at the practical side of things:

All of my personal projects, including MobiMap, will certainly benefit from this new enlightenment. And I sincerely hope that my day-to-day job will give me the opportunity to work with those concepts…

What’s there after Objects?

As far as I can tell, there has been 3 major “revolutions” in software development since it all started:

  1. From binary to assembly language
  2. From assembly language to procedural languages
  3. From procedural languages to Object-Oriented Programming

Of course I’m not even talking about marginal evolutions like functional programming, scripting or formal programming.

And behind a revolution, there’s always a massive “there’s gotta be a better way” feeling. For assembly language people probably thought, “since we’re working with registers and memory addresses and instructions, let’s have readable forms of these concepts rather than just hexadecimal code, obviously we’re going to be more productive”. And then it was probably the same with procedural vs. OOP: Objects, classes, fields and methods were just closer to the kind concepts we were manipulating at some point and we couldn’t just keep tinkering with old paradigms, even on steroids (read structures and things like that).

Now I’m starting to wonder whether we’ve not come to the same point with OOP. At least I have come to this point myself. Objects, packages, components, whatever the granularity I’m still stuck having to tinker with old stuff to realize higher level tasks at some point. Most of the time, I’m not thinking about adding a field or a method in an object, but instead I want to add a property to an entity in my domain, or expose a business operation via a webservice. That’s the kind of tasks that make my day-to-day work. And still, let’s say I want to add a property to an entity in my domain, then I have to add the corresponding field in a class, write a getter and a setter, update the DDL script for the database, add the mapping to the Hibernate mapping file, add a validation directive somewhere… there’s gotta be a better way.

Now I realize that’s the main reason I love AndroMDA so much: because I can do high-level modifications in my UML models and boom! The generator just takes it over from there and updates the code almost everywhere it needs to be, which improves my productivity by a tremendous factor. Others use other tricks for the very same purpose: some use annotations, others turn to active record implementations. But whatever the trick, I feel more and more like it’s a dead-end, like… there’s gotta be a better way.

The closer the tools I’m using are to the concepts I manipulate, the less work I have to do to implement those concepts, the better it is for the whole project:

  • it reduces the probability for errors
  • it improves time-to-market
  • it frees up some time to focus on the real business at hand
  • it gives me a better sense of achievement
  • it dramatically improves return on investment since basically you’re doing more with less

Tonight I had a very interesting conversation with a very smart guy from the AndroMDA team, and it just appeared to me like magic: AndroMDA is just one way to cope with limitations of the underlying object-oriented paradigms, and we have to start thinking about how we can reach the same goals, but in a more native way. We need a brand new paradigm, a new way to build software closer to what we try to achieve everyday at a higher level.

What do you guys think? Have you heard of anything like that? Because I would be really interested in knowing about it. Otherwise, does anyone have any idea about what could be this new paradigm? And do you feel we need it? I’m really interested in your feedback on that one.

Goal-Driven Development

It’s always amazing to see how people find it hard to compromise, to nuance their opinions about things. And I’m probably the first one finding it hard. But when it comes to software practices, boy it’s annoying.

I was talking to a colleague of mine the other day, we were talking about unit testing and other best practices, and I boldly and shamelessly said to him: “I haven’t written any unit test on this project.” He stared at me with a bit of surprise, then with a bit of disappointment and finally with a bit of something like… disgust!

“What!? No tests, but why? How can you pretend to be a software architect if you don’t practice systematic unit testing?! Oh my god!…”

My first reaction was a furious urge to hit him in the face. But then I remembered myself a few years back, and I did nothing but leave him in his panic state and disappointment.

When I started working as a consultant, I had already written a few applications in engineering school, but strangely enough they didn’t really talked to us about software quality, agile methodologies and other modern best practices. We did formal programming, Prolog, we reprogrammed a memory management unit and wrote a compiler for a subset of the Java language, but nothing useful ;o).So when I discovered that some people were actually doing things in a rational way, to write better software, I was at the same time impressed and overwhelmed by all of that. Design patterns, continuous integration, test-driven development… I had never seen those in the real world, but I read a lot of books and websites and it seemed so nice that I came to think that it was the only way. And of course I was wrong.Fortunately, I started working on real-world projects, dealing with all sorts of external constraints. And no matter how hard I tried to impose “my” great software best practices, everybody looked at me like an alien because they just didn’t understand why I was talking about all this stuff. So when I was fed up with complaining about no one understanding what should be done, I realized that they were at least right to wonder. Why are things like TDD, CI or Design Patterns so important?

When you read so many articles explaining to you how to write unit tests, they all seem to assume that unit-testing is good in itself, as if it was some kind of axiom. But the truth is that no matter how good they are, writing them and maintaining them is a real pain, right? Lesson learned: when something is painful but good for you, there’s gotta be a better way. But a better way to what?

Because for me that’s the real problem: losing sight of the objective. Unit-testing and TDD are not good in themselves, they are just one best practice which allows you to improve the overall quality and robustness of your code. Why so? Because when you write your tests before the corresponding functional code, you considerably reduce the probability of a bug in the functional code. And robustness comes from the fact that whenever the implementation of a given functionality is modified over time, unit tests are there to ensure that the overall result will remain the same. Fine! But how about a better way?

First, let’s talk about reducing the probability of bugs. The main problem with code is that it’s written by us, human beings. And like it or not, we are faillible, we make mistakes, and the more we think we don’t, the more we actually do. Now rather than testing everything that we write, isn’t there a way to reduce the amount of code that we have to write? I can tell you that: there is a way!

I already see my colleague smiling if he reads this, because I’m so obsessive about this “way” that it becomes ridiculous. Take care, here comes the dirty words: code generation. Of course I’m not talking about the kind of code generation that just displaces the problem elsewhere, that is in diagrams that are the ont-to-one mapping of your code. I’m talking of a higher level of code generation, I’m talking of Model-Driven Architecture.

I know that many programmers don’t like it, have read many articles about and introductions to MDA without ever going further, mostly because programmers like to… program, not draw. And I can understand that. And if you’re in that situation, then you’re stuck with test-driven development… or any other “way” you can find. But if you like to have a better view of the big picture, if you want to accelerate your development and increase the robustness and quality of your code, then have a look at this (my favourite), this and this. You might be surprised.

Will it completely replace unit tests? I don’t think so, but it can create a situation in which you have so dramatically reduced the amount of code to test, that it can be interesting to wonder whether it’s still worth the effort.

My main point is, software best practices are nothing without the goal they allow you to reach, and forgetting that is the best way to stop looking for better ways, to stop innovation and progress.