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Today I'm going to talk to you about WebMock, a Ruby gem for mocking HTTP requests.
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First, a little bit about me.
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I've been developing software for over 20 years. Back in 2006, when I was still a Java developer, my friend Andre KDA came to me.
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He asked, 'Hey, have you heard of that new language called Ruby?' I've been using Ruby ever since.
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Professionally, I've been using Ruby since 2007. I live in Wroclaw but have been working remotely since before it was trendy.
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I'm the author and the sole maintainer of WebMock.
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Today, I'm a little stressed because this is my first presentation in 14 years.
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After seeing all these great presentations today, I feel the bar has been raised.
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Being the final speaker of the day is a unique experience.
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This is also my second presentation about WebMock; the previous one was in London 15 years ago. I was still stressed then, and nothing has changed.
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After seeing David Halas speak yesterday about formal languages, I thought I should add a slide about something I learned at my university.
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This led me to think about extrapolation, so I extrapolated when my next talk about WebMock would be.
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We have a unique chance to learn something about WebMock today.
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So, what is WebMock? WebMock has two core functionalities.
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First, it allows you to stub HTTP requests. This means you can declare fake responses so that when your application attempts to make an HTTP request, no connection is made, and instead, a fake response is returned.
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Second, it allows you to verify that HTTP requests have been executed, whether they are stubbed or real.
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The idea is not original; there was a gem called FakeWeb before. I tried to use it, but its request matching capabilities were too limited, and it only supported Net::HTTP.
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Therefore, I decided to write my own solution and created WebMock during a hackathon.
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The first version of WebMock was developed to address my own needs as a Ruby developer.
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These needs turned out to be the needs of many other Ruby developers as well, and hence, WebMock has been downloaded more than 250 million times up until now.
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It has almost 4,000 stars on GitHub; by the way, if you haven't starred it yet, please do. I'm aiming for 4,000.
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Over 260 people have contributed to WebMock over the last 15 years, and I would very much like to thank everyone who has ever contributed.
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WebMock is used by thousands of public projects on GitHub, and almost 8,000 registered gems depend on it.
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Some of the projects that depend on WebMock are listed here, and you might have heard of or used some of them.
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If you haven't had a chance to use any of them, you probably have used this one. Machi mentioned today that if you know something, you should publish it.
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So I want to encourage you, if you have a solution that works for you, to publish it. It might be useful to others.
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WebMock has also inspired developers in other languages, leading to the creation of solutions inspired by WebMock.
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I've even seen the term 'web mocking' used to refer to mocking HTTP requests.
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So, what can you do with WebMock? First, WebMock provides a nice domain-specific language (DSL) for declaring request stubs.
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It is easily readable and understandable. Second, it offers a DSL for verifying that HTTP requests have been made. Both DSLs are HTTP client agnostic, so you can use them with any HTTP client.
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WebMock follows the stub, execute, verify paradigm, which I borrowed from a Java testing framework called Mockito.
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It separates the stubbing phase from the verification phase, which might be different from frameworks like RSpec, where a single expect declaration defines both the stub and the expectation.
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In WebMock, the steps are separated, allowing you to stub without verifying or verifying without stubbing.
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WebMock offers request callbacks, and with these callbacks, you can record requests.
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There is a gem called VCR for recording HTTP requests, which uses WebMock under the hood.
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WebMock offers many features for stubbing; for example, you can stub requests to timeout or with basic authentication.
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You can even replay raw responses recorded with curl.
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WebMock supports all popular HTTP clients in Ruby and all major testing frameworks.
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But then you might ask, why mock HTTP requests at all? Why should we care?
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First, it allows you to run your tests without needing an internet connection.
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For anyone, like me, who arrived here by train and has been working on a train, this is a useful feature.
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If you misconfigure your testing environment and accidentally use production credentials, with WebMock, your tests won't make any delete requests on a production third-party API.
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You always get a stable environment for running your tests.
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Even if a third-party service is down or temporarily returns 500 responses, your tests will still go through and pass.
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You also get fast tests, as you don't have to wait for any API delays—your responses are instant.
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You can also test various scenarios, such as different status codes and error responses, and see how your app reacts to them.
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All this test setup is done in Ruby files.
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Mocking HTTP requests is not only useful for testing environments; you can also define your request stubs in the development environment and work offline.
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You can set request stubs for various scenarios and test your app manually while simulating different situations.
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One feature that I have used many times in the past is that it allows you to develop without access to a third-party API.
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For example, I once worked on a project that heavily relied on a third-party API.
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We received access to it only after a month and a half.
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In the meantime, we read the documentation and API specifications, created some stubs, and were ready to go.
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You can do the same in your development environment to demo the features that have been implemented, even before you have access to the external API.
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Now, let me show you a sample Rails initializer for development and staging.
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So, we know that stubbing HTTP requests can be useful at times.
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But why would we use WebMock instead of creating our own solution?
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Let's say we find a piece of code in our app that makes an HTTP request with basic authentication.
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We are going to make a change to it, so we search for a test because we do test-first development, and we change the test first before changing the actual behavior.
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We find the test, and the setup looks completely unreadable.
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So what do I do first? Well, I first do a Git blame and find out who wrote it, and then I realize it was me five years ago.
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This has happened many times.
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Then I take WebMock and change my test; the setup is much simpler.
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Now I can change my code and don't have to use the complicated Net::HTTP interface.
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Instead, I can use an HTTP gem that has a nice DSL for making requests.
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WebMock is great for test-driven development (TDD). You can write your tests first, focusing on the expected behavior.
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You don't have to think about which library you are going to use or what methods you are going to call.
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You just want to define the expected behavior, such as what HTTP requests will be made and what responses will be returned.
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You can think about the implementation later.
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WebMock is also very useful for legacy applications.
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One of the first things I would do when taking over some legacy code is to import WebMock and enable it.
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Now I'm safe; I know that when I run the app in development or run tests, it won't make unexpected requests to a third-party API without my knowledge.
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If it makes any requests, WebMock will alert me.
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WebMock allows me to define request stubs with unescaped versions of URLs.
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I find this feature very useful for having credible tests; escaped URLs are much harder to read.
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Another feature I really like about WebMock is the stubbing instructions.
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When you have a request stub that doesn't match, for any reason—whether the request stub is wrong or the wrong request is executed—WebMock will intercept it.
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It raises an error and prints instructions telling you how to stub the request.
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It also tells you what the currently registered request stubs are.
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Basically, I created WebMock to simplify things for myself, and it also makes things simpler for others.
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But with all this DSL, comes some magic.
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You see the DSL declaration, but you lose control; you don’t know what actually happens underneath.
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If you are like me, you like to understand how things work underneath.
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About two months ago, I went to a presentation by Javier, who explained Sidekiq internals.
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I found it very insightful and thought, 'Okay, I'll do the same for WebMock. I'll explain how WebMock works underneath.'
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However, to understand how WebMock works internally, we first need to understand how HTTP clients in Ruby work.
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Let's take a sample HTTP client in Ruby.
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It usually has some public interface and public methods that represent HTTP verbs.
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These methods are usually very simple; they don’t do much.
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They typically call some private methods that do all the heavy lifting.
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So let's look at how that method might be structured and what it does.
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First, it will build the request, parse the headers, and add any default headers.
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Then it creates the complete request object.
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If the HTTP client supports it, it might run some request middleware on it.
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Once all the request data is complete, it will send it through a TCP or SSL connection.
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When a response is received from that connection, it might run some response middleware on it before returning the final response.
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That's how a typical HTTP client works.
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Of course, there are many differences; for example, there are asynchronous clients.
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Some clients use C bindings instead of talking directly to TCP or SSL connections.
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However, more or less, this is how a typical HTTP client in Ruby works.
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Now that we know how HTTP clients in Ruby work, we can understand how WebMock works internally.
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Let's first focus on stubbing and what happens when we call stub request.
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If we have a stub request declaration, WebMock will create a request stub object and register it inside the global stub registry.
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The request stub object consists of a request pattern that is used to match requests and a collection of fake responses that will be returned if a matching request is detected.
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The stub request method returns the request stub itself, allowing us to chain additional calls.
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For example, we can call 'with' to extend the request pattern with additional criteria.
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Now our request stub will only match requests that have a body of 'F' and a content type of 'JSON' header.
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Again, our request stub is being returned, which allows us to call the 'to_return' method to create a fake response object and associate it with the request stub.
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Now, regarding registering callbacks, it’s quite simple: we pass a block, and that block gets registered in the global callback registry.
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So now we have this global stub registry with registered request stubs and a registered callback.
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But nothing actually changes right now; no requests are being intercepted.
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That’s where WebMock uses adapters.
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WebMock has an implementation adapter for each of the HTTP clients in Ruby; one adapter per client.
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Let's implement an adapter for our sample HTTP client.
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First, it will create a copy of the handle request method, which does all the heavy lifting.
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WebMock will take the class that contains that method and create a copy of it by subclassing.
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Then it will start monkey patching the class.
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After the request is built, it will create a request signature and register that signature in the request registry.
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This signature contains all required information to match the request.
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Next, it checks the stub registry to see if there is any request stub matching the request.
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If there is, it will return a fake response; if not, it will make a real request.
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However, WebMock blocks all real connections by default.
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So we have to extend the handle request method to allow making the real request if specifically configured.
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If not, we raise an error, which will give us a nice stubbing instruction when the response is returned.
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We also run any registered callbacks and then run any middleware supported by that HTTP client before returning the response.
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Now we have a copy of a class that has been instrumented by monkey patching, but it still doesn't change the original behavior.
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For instance, if I call sample HTTP client get, it will still call the original class and make the real request.
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The adapter needs to do something more.
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Let’s go over how handle request works. First, it builds the request, creates the request signature, and registers it in the request registry.
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If a matching request stub is found, a fake response is used.
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If a real request is allowed, we’ll make a request and return a real response.
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Otherwise, we raise an error and print stubbing instructions.
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Finally, we call any registered callbacks, response middleware, and return the response.
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So, how does WebMock affect the original sample HTTP client class?
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First, it creates a reference to the original class, which will be useful in the future.
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Then, it replaces the original class using constant replacement.
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Thus, the client constant will now point to our monkey-patched version.
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While monkey patching can be problematic, I find this solution neat since we are not modifying the original class.
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If needed, we can always revert all changes by doing constant replacement and restoring the original class.
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When we enable WebMock, this will enable the adapter, replacing the original class with our monkey-patched class.
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When we call stub request, it registers the stub in the stub registry with a fake response declared earlier.
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Once we execute the request, it will return a fake response from the registry.
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Now we can proceed further. Remember the request signatures we registered in the handle request method?
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We can verify that those requests were executed.
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We create a request pattern and check the request registry to find if there is any request signature matching that pattern.
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This is how WebMock works.
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I want to share something special and very important to me.
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I created WebMock to address my own needs as a Ruby developer.
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I created WebMock during a company hackathon.
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But it wasn’t just any company and not with any people.
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Back in 2009, I lived in London and worked for a company called New Bamboo.
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New Bamboo comprised a team of passionate developers.
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We called ourselves 'Bambinos,' and I believe each of us was very proud to be part of that team.
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We shared our passion, motivated each other, inspired one another, supported each other, and encouraged one another.
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During my over 20 years of building software, I have learned that the most important thing for your growth is the people you work with and what you learn from them.
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When L. Stal said that Ruby people are strange, I believe he was right.
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To me, Ruby has always been not just about writing nice code or using Rails.
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It was mainly about the people—those who shared their passion, inspired each other, and were friendly.
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This event, this conference, WrocLove.rb, is the essence of that.
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I would very much like to thank everyone who organizes WrocLove.rb, or has ever organized it.
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What you all are doing is really important for our community.
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Thank you.
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All right, do we have any questions?
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Sorry, just ice breaker. Okay, no one? Alright, oh, there is one.
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First, I just want to thank you because I've been using WebMock since the first version you pushed.
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As long as I can remember, I've been using WebMock and still use it today, so that is great.
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I want to mention something very important: it's crucial to know when a mock is no longer valid.
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In the applications I’ve used, we’ve been doing contract testing to know when things changed and when the mocks had to be updated.
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I wonder if you have thought about or tried to build anything for contract testing alongside WebMock or as a separate library?
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No, I haven't. However, the scope of validation is something that is consistently on my mind.
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The fact that WebMock uses global registries is a problem because you either have to reset them or keep using them.
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It's not trivial to say, 'I want this mock to only be valid within this scope or this thread.'
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I hear from time to time that users want to reduce this scope.
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I hope that some major next version of WebMock will support this.
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Thank you.
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In other words, Bartosz is saying he needs contributors.
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There's one more question. Thanks for a great presentation.
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I wonder, because WebMock cooperates with various HTTP libraries, how do you keep track of the changes in those libraries?
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How do you ensure that WebMock correctly monkey patches them?
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WebMock tries to be up to date with the latest versions.
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The WebMock gemfile doesn’t have hardcoded versions or any restrictions.
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The tests will always update to the latest version of a gem when testing.
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This means that some older versions may no longer work with WebMock.
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WebMock always tries to stay up to date with the latest HTTP gem version.
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However, there is no automated system for that.
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Usually, I learn about incompatibilities either by rerunning the test suite or through users raising issues.
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Often, users first open an issue in the HTTP client repository.
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Then, the maintainer of that specific gem submits a pull request, or someone from the contributors raises an issue.
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These types of issues are given priority because they affect people.
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This is an emergency.
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Okay, there’s one more chance to ask a question.
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I see no one. Okay, ladies and gentlemen, Bartosz Blimke once again.
