Various test runners support using compiled webpack code to drive tests, but may be difficult to integrate with webpack, and Neutrino helps alleviate this

But what you absolutely should do is test your NPM package in its published format. Create some smoke tests that reside in the actual codebase, but are not part of the test suite.

Testing is hard. For most developers, testing is a sad story.

In React, there are different aspects of UI Testing. We categorize them as follows along with their tooling:

Storybook integrates with Jest Snapshot through an add-on called StoryShots. StoryShots adds automatic Jest Snapshot Testing to our codebase by using our existing Storybook stories as the input for Jest Snapshot Testing.

The most common phrase in a Pull Request (PR) is: Please add the tests

Since the checkbox is rendering an input I would work with it rather than focusing on the image. You could do something like this: const checkbox = getByTestId('checkbox-1234').querySelector('input[type="checkbox"]') expect(checkbox).toHaveProperty('checked', true)

the way Material UI works is it renders a different SVG when the checkbox is clicked, and not changing the attributes or anything on the actual input element. So how do I actually test that the element is checked in line with the react-testing-library philosophy?

If you're writing a tool for developers, it's a really common case that you want to write a test to ensure that a good error or warning message is logged to the console for the developers using your tool. Before snapshot testing I would always write a silly regex that got the basic gist of what the message should say, but with snapshot testing it's so much easier.

These four things lead to a near total loss in the intended utility of integrated/functional tests: as the code changes make sure nothing is broken.

(After all, it's not like the past snapshot was well understood or carefully expressed authorial intent.) As a result, if a snapshot test fails because some intended behavior disappeared, then there's little stated intention describing it and we'd much rather regenerate the file than spend a lot of time agonizing over how to get the same test green again.

They are generated files, and developers tend to be undisciplined about scrutinizing generated files before committing them, if not at first then definitely over time. Most developers, upon seeing a snapshot test fail, will sooner just nuke the snapshot and record a fresh passing one instead of agonizing over what broke it.

Good tests encode the developer's intention, they don't only lock in the test's behavior without editorialization of what's important and why. Snapshot tests lack (or at least, fail to encourage) expressing the author's intent as to what the code does (much less why)

I very rarely use snapshot testing with react and I certainly wouldn't use it with shallow. That's a recipe for implementation details. The whole snapshot is nothing but implementation details (it's full of component and prop names that change all the time on refactors). It'll fail any time you touch the component and the git diff for the snapshot will look almost identical to the one for your changes to the component.This will make people careless about to the snapshot updates because they change all the time. So it's basically worthless (almost worse than no tests because it makes you think you're covered when you're not and you won't write proper tests because they're in place).

I should also add that I'm in favor of relying more heavily on integration testing. When you do this, you need to unit test fewer of your simple components and wind up only having to unit test edge cases for components (which can mock all they want).

But isn't the point of testing to be confident the application works? Who cares if your unit works if the app is broken? I definitely want to know if the third party component I'm using breaks my use case. I mean, I'm not going to rewrite their entire test base, but if I can easily test my use case by not mocking out their component then why not do that and get the extra confidence?

it doesn't even render in-file components. For example, the <Fade /> component we have above is an implementation detail of the <HiddenMessage /> component, but because we're shallow rendering <Fade /> isn't rendered so changes to that component could break our application but not our test. That's a major issue in my mind and is evidence to me that we're testing implementation details.

The reason this kind of test fails those considerations is because it's testing irrelevant implementation details. The user doesn't care one bit what things are called. In fact, that test doesn't even verify that the message is hidden properly when the show state is false or shown when the show state is true. So not only does the test not do a great job keeping us safe from breakages, it's also flakey and doesn't actually test the reason the component exists in the first place.

I could rename toggle to handleButtonClick (and update the corresponding onClick reference). My test breaks despite this being a refactor.

I could mistakenly set onClick of the button to this.tgogle instead of this.toggle. My test continues to work, but my component is broken.

let's add a console.log(wrapper.debug()) which will log out the structure of what enzyme has rendered for us

Will this test break when there's a mistake that would break the component in production?Will this test continue to work when there's a fully backward compatible refactor of the component?

So finally I'm coming out with it and explaining why I never use shallow rendering and why I think nobody else should either. Here's my main assertion:With shallow rendering, I can refactor my component's implementation and my tests break. With shallow rendering, I can break my application and my tests say everything's still working.This is highly concerning to me because not only does it make testing frustrating, but it also lulls you into a false sense of security. The reason I write tests is to be confident that my application works and there are far better ways to do that than shallow rendering.

For instance, an integration test could verify that all necessary props are passed through from the tested component to a specific child component.

Often, if you are writing a test that amounts to “it does what it does”, or “it does exactly this, which happens to be duplicated in the application code”, then the test is either unnecessary or too broad.

Here are three rules of thumb I use to determine that something is not worth testing:Will the test have to duplicate exactly the application code? This will make it brittle.Will making assertions in the test duplicate any behavior that is already covered by (and the responsibility of) library code?From an outsider’s perspective, is this detail important, or is it only an internal concern? Can the effect of this internal detail be described using only the component’s public API?

Yes, we've violated that "one assertion per test" rule, but that rule was originally created because testing frameworks did a poor job of giving you the contextual information you needed to determine what was causing your test failures.

When you mock something, you're making a trade-off. You're trading confidence for something else. For me, that something else is usually practicality — meaning I wouldn't be able to test this thing at all, or it may be pretty difficult/messy, without mocking. (Like in our credit card example.)

You’ll rest easy at night, knowing that the proper amount of automated test coverage is in place and protecting your product from unintentional breakage.

But far too often, I see tests which are testing implementation details (read this before continuing if you haven't already). When you do this, you introduce a third user. The developer user and the end user are really all that matters for this component. So long as it serves those two, then it has a reason to exist. And when you're maintaining the component you need to keep those two users in mind to make sure that if you break the contract with them, you do something to handle that change.But as soon as you start testing things which your developer user and end user don't know or care about (implementation details), you add a third testing user, you're now having to keep that third user in your head and make sure you account for changes that affect the testing user as well.

"The more your tests resemble the way your software is used, the more confidence they can give you. "

Why is testing implementation details bad?There are two distinct reasons that it's important to avoid testing implementation details. Tests which test implementation details:Can break when you refactor application code. False negativesMay not fail when you break application code. False positives

Unit test coverage grants confidence that code logic is correct(and serves as great developer documentation!)

You want to write maintainable tests for your React components. As a part of this goal, you want your tests to avoid including implementation details of your components and rather focus on making your tests give you the confidence for which they are intended. As part of this, you want your testbase to be maintainable in the long run so refactors of your components (changes to implementation but not functionality) don't break your tests and slow you and your team down.

This library is a replacement for Enzyme.

We try to only expose methods and utilities that encourage you to write tests that closely resemble how your web pages are used.

The more your tests resemble the way your software is used, the more confidence they can give you.

Most of the damaging features have to do with encouraging testing implementation details. Primarily, these are shallow rendering, APIs which allow selecting rendered elements by component constructors, and APIs which allow you to get and interact with component instances (and their state/properties) (most of enzyme's wrapper APIs allow this).

“Code without tests is broken by design”

Here are my tools of choice for testing React apps:react-test-renderer for snapshot unit testingAct API for unit testing React componentsJest for unit and integration testing of JavaScript codeCypress for end to end / ui testing

In Double-loop TDD it’s functional testing that drives our development. We write a functional test for testing that our application satisfy some user stories. When the functional test fails we move to write unit and integration tests which in turn drive how we code our components.

I don't recommend unit testing stateful components, or components with side-effects. Write functional tests for those, instead, because you'll need tests which describe the complete end-to-end flow, from user input, to back-end-services, and back to the UI. Those tests frequently duplicate any testing effort you would spend unit-testing stateful UI behaviors. You'd need to do a lot of mocking to properly unit test those kinds of components anyway, and that mocking may cover up problems with too much coupling in your component.

The amount of dev time it saves is uncanny. Like, what used to take 3 hours to write now takes like 30 minutes. No joke.

If you’re dedicated to reducing flakiness, you can take this a step further and reduce flake in your tests even more by killing timers that are set in your tests:

Snapshot testing is great as it let us capture strings that represent our rendered components and the store it in a separate snapshot file to compare later in order to ensure that UI is not change. While it is ideal for React apps, we can use snapshots for comparing values that are serialized from other frameworks.

Screenshot Test: Applications are not often screenshot tested. However, if the business requirement is there, screenshot tests can be used to diff two screenshots from the same application state in order to verify whether something (styling, layout, …) has changed. It’s similar to a snapshot test, whereas the snapshot test only diffs the DOM and the screenshot test diffs screenshots.

Snapshot Test: Introduced by Facebook’s library Jest, Snapshot Tests should be the lightweight variation of testing (React) components. It should be possible to create a DOM snapshot of a component once a test for it runs for the first time and compare this snapshot to a future snapshot, when the test runs again, to make sure that nothing has changed. If something has changed, the developer has to either accept the new snapshot test (the developer is okay with the changes) or deny them and fix the component instead.

The process of learning effective TDD is the process of learning how to build more modular applications.

Hopefully, the implementation is buggy enough that people will report bugs and that we will add tests for.

The issue that had roiled the grown-ups in his life seemed to have had no effect on him at all.

A 95 percent opt-out rate was a resounding success. It rivaled election results in Turkmenistan.

been set. This

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his, too, is false. Indeed, the data from released national tests show conclusively that the students have the most difficulty with those items that require understanding and transfer, not recall or recognition.

This perceived incompatibility is based on a flawed assumption that the only way to raise test scores is to cover those things that are tested and practice the test format.

drive development using an outside-in testing approach:

excess toxicities withparticular cytotoxic therapies

120 developer minutes/day spent waiting

Particle-Based Approximate Inference

const sinon = require('sinon'); const mockResponse = () => { const res = {}; res.status = sinon.stub().returns(res); res.json = sinon.stub().returns(res); return res; };

A field study at Google[4] covering over 100,000 consumer-grade drives from December 2005 to August 2006 found correlations between certain S.M.A.R.T. information and annualized failure rates: In the 60 days following the first uncorrectable error on a drive (S.M.A.R.T. attribute 0xC6 or 198) detected as a result of an offline scan, the drive was, on average, 39 times more likely to fail than a similar drive for which no such error occurred. First errors in reallocations, offline reallocations (S.M.A.R.T. attributes 0xC4 and 0x05 or 196 and 5) and probational counts (S.M.A.R.T. attribute 0xC5 or 197) were also strongly correlated to higher probabilities of failure. Conversely, little correlation was found for increased temperature and no correlation for usage level. However, the research showed that a large proportion (56%) of the failed drives failed without recording any count in the "four strong S.M.A.R.T. warnings" identified as scan errors, reallocation count, offline reallocation and probational count. Further, 36% of failed drives did so without recording any S.M.A.R.T. error at all, except the temperature, meaning that S.M.A.R.T. data alone was of limited usefulness in anticipating failures.[5]

Students require a variety of learning situations and opportunities in order to be aware of and reflect on...variation, and to be able to make fine distinctions about the significant aspects of each new context. By identifying the differences between similar situations, the student is better able to respond appropriately. Such learning experiences are an important preparation for the unpredictable nature of the workplace

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A village scoring 1.5 and another scoring 1.49 would be almost equally insecure.

Then inject it inside a test by calling TestBed.get() with the service class as the argument. it('should use ValueService', () => { service = TestBed.get(ValueService); expect(service.getValue()).toBe('real value'); });

However, you almost always inject service into application classes using Angular dependency injection and you should have tests that reflect that usage pattern. Angular testing utilities make it easy to investigate how injected services behave.

We can even remove the AuthService import if we want, there really is no dependency on anything else. The LoginComponent is tested in isolation:

That’s not very isolated but also not too much to ask for in this scenario. However imagine if LoginComponent required a number of other dependencies in order to run, we would need to know the inner workings of a number of other classes just to test our LoginComponent. This results in Tight Coupling and our tests being very Brittle, i.e. likely to break easily. For example if the AuthService changed how it stored the token, from localStorage to cookies then the LoginComponent test would break since it would still be setting the token via localStorage.

Mocking localStorage is optional, but without mocking getComputedStyle your test won’t run, as Angular checks in which browser it executes. We need to fake it.

Or inside the beforeEach() if you prefer to inject the service as part of your setup. beforeEach(() => { TestBed.configureTestingModule({ providers: [ValueService] }); service = TestBed.get(ValueService); });

Something that I've found helps greatly with testing is that when you have code with lots of nested function calls you should try to refactor it into a flat, top level pipeline rather than a calling each function from inside its parent function. Luckily in clojure this is really easy to do with macros like -> and friends, and once you start embracing this approach you can enter a whole new world of transducers. What I mean by a top level pipeline is that for example instead of writing code like this: (defn remap-keys [data] ...some logic...) (defn process-data [data] (remap-keys (flatten data))) (defn get-data [] (let [data (http/get *url*)] (process-data data))) you should make each step its own pure function which receives and returns data, and join them all together at the top with a threading macro: (defn fetch-data [url] (http/get url)) (defn process-data [data] (flatten data)) (defn remap-keys [data] ...some logic...) (defn get-data [] (-> *url* fetch-data process-data remap-keys)) You code hasn't really changed, but now each function can be tested completely independently of the others, because each one is a pure data transform with no internal calls to any of your other functions. You can use the repl to run each step one at a time and in doing so also capture some mock data to use for your tests! Additionally you could make an e2e tests pipeline which runs the same code as get-data but just starts with a different URL, however I would not advise doing this in most cases, and prefer to pass it as a parameter (or at least dynamic var) when feasible.

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Douglas Crockford 2018-08-24 JSCheck is a testing tool for JavaScript. It was inspired by QuickCheck, a testing tool for Haskell developed by Koen Claessen and John Hughes of Chalmers University of Technology. JSCheck is a specification-driven testing tool. From a description of the properties of a system, function, or object, it will generate random test cases attempting to disprove those properties, and then report its findings. That can be especially effective in managing the evolution of a program because it can show the conformance of new code to old code. It also provides an interesting level of self-documentation, because the executable specifications it relies on can provide a good view of the workings of a program.

Nightwatch.js is an easy to use Node.js based End-to-End (E2E) testing solution for browser based apps and websites. It uses the powerful W3C WebDriver API to perform commands and assertions on DOM elements.

Let’s think of some properties for the rectangle area function: Given any two width and height values, the result is always a multiple of the two Order doesn’t matter. A rectangle which is 50×100 has the same area as one which is 100×50 If we divide the area by width, we should get the height Here we have three examples of how we can verify the test result for any given input without having to know the inputs up front. All of these should always hold true for any given valid input.

JSVerify is a property-based testing library, highly inspired by QuickCheck. It is testing framework agnostic, you could use JSVerify with Mocha, nodeunit, Jasmine or any other framework.

Javascript

Then it gets the native element of the compiled HTML (the HTML rendered by the component).

We use an async before each. The purpose of the async is to let all the possible asynchronous code to finish before continuing.

The CLI takes care of Jasmine and karma configuration for you.