Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a React component which contains some other components that depend on access to a Redux store etc.
Let's say a structure like this:. I want to use Jest's. I've tried to return a function instead, however you can't return JSX from what I could tell in a Jest mock, due to it being hoisted. It throws an error in this case. There's a note at the bottom of the docs for jest. Note: When using babel-jestcalls to mock will automatically be hoisted to the top of the code block.
Testing React Components with Enzyme and Jest
Use doMock if you want to explicitly avoid this behavior. Then you can do as you described: return a function that is a stub of the component you don't need to test. I've learned a little more since I asked this question.
Here's an alternative better? If the underscores upset you, just pretend they aren't there. Then in the test file, change the Jest mock statement to: jest. When Jest encounters a. However, even though the mock statement gets hoisted in the component being tested, this doesn't affect the imports of the mock itself - hence why it's able to import and compile a React component!
This seems to work well for mocked components that need to be passed props, and would otherwise produce prop warnings if a nulled function was returned but which is perfectly acceptable to continue using if the component does not receive props. I hope this helps some people out there. Learn more. Using Jest to mock a React component with props Ask Question. Asked 2 years, 10 months ago.
Active 1 year, 5 months ago. Viewed 35k times. Let's say a structure like this: import ComponentToMock from '. I'm aware that I can mock out a straight component with something like: jest.Mocking ES6 imports is really useful for being able to test modules; however, my usual technique of using a Webpack loader doesn't work with Jestsince Jest is called from Node and doesn't run test code through Webpack.
Instead, we have to use Jest's mocking functions to replace the import with a stub file. This is the component we're going to test - it has a button to be able to select a folder in an Electron app.
We want to be able to check that the dialogue was called and that our doSomethingWithPath function was called with the response from the dialogue.
Testing React Apps
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Basically I am trying to mock the homeContext. Learn more. Trying to use Jest manual mocking to mock a Higher Order Wrapper function but the mocked component never gets hit Ask Question. Asked yesterday. Active yesterday. Viewed 15 times. Didar Charania Didar Charania 1 1 1 bronze badge. New contributor. Active Oldest Votes. Didar Charania is a new contributor. Be nice, and check out our Code of Conduct.
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Technical site integration observational experiment live on Stack Overflow. Triage needs to be fixed urgently, and users need to be notified upon….Mock functions allow you to test the links between code by erasing the actual implementation of a function, capturing calls to the function and the parameters passed in those callscapturing instances of constructor functions when instantiated with newand allowing test-time configuration of return values.
There are two ways to mock functions: Either by creating a mock function to use in test code, or writing a manual mock to override a module dependency. Let's imagine we're testing an implementation of a function forEachwhich invokes a callback for each item in a supplied array.
To test this function, we can use a mock function, and inspect the mock's state to ensure the callback is invoked as expected. All mock functions have this special.
These mock members are very useful in tests to assert how these functions get called, instantiated, or what they returned:. Mock functions are also very effective in code that uses a functional continuation-passing style.
Code written in this style helps avoid the need for complicated stubs that recreate the behavior of the real component they're standing in for, in favor of injecting values directly into the test right before they're used. Most real-world examples actually involve getting ahold of a mock function on a dependent component and configuring that, but the technique is the same. In these cases, try to avoid the temptation to implement logic inside of any function that's not directly being tested.
Suppose we have a class that fetches users from our API. The class uses axios to call the API then returns the data attribute which contains all the users:. Now, in order to test this method without actually hitting the API and thus creating slow and fragile testswe can use the jest.
Once we mock the module we can provide a mockResolvedValue for. In effect, we are saying that we want axios. Still, there are cases where it's useful to go beyond the ability to specify return values and full-on replace the implementation of a mock function.
This can be done with jest. The mockImplementation method is useful when you need to define the default implementation of a mock function that is created from another module:.
When you need to recreate a complex behavior of a mock function such that multiple function calls produce different results, use the mockImplementationOnce method:.
When the mocked function runs out of implementations defined with mockImplementationOnceit will execute the default implementation set with jest. For cases where we have methods that are typically chained and thus always need to return thiswe have a sugary API to simplify this in the form of a. You can optionally provide a name for your mock functions, which will be displayed instead of "jest. Use this if you want to be able to quickly identify the mock function reporting an error in your test output.
Finally, in order to make it less demanding to assert how mock functions have been called, we've added some custom matcher functions for you:. These matchers are sugar for common forms of inspecting the. You can always do this manually yourself if that's more to your taste or if you need to do something more specific:. Using a mock function Let's imagine we're testing an implementation of a function forEachwhich invokes a callback for each item in a supplied array.
It will also assert on the name.Everyone who is new to React is confused by these so called props, because they are never mentioned in any other web framework, and rarely explained on their own.
They are one of the early things you will learn in React after initially grasping React's JSX syntax. Basically props are used to pass data from component to component. In this guide, I want to explain React props in greater detail.
First, it explains the "What are props in React? Normally you start out with React's JSX syntax for rendering something to the browser when learning about React.
A common question followed by this act: how to pass the data as params parameters from one React component to another component? That's because you don't want to have a component rendering static data, but pass dynamic data to your component instead. That's where React's props come into play. So don't forget the curly braces. As you can see, the props are received in React's class component via the this instance of the class. A common question which comes up then: Why aren't the props received in the render methods signature?
It would be similar to functional stateless components then. As for now, the team behind React considered it, but didn't change the API for React class components yet. Maybe it will be changed at some point. In a functional stateless component, the props are received in the function signature as arguments:.
Since you will find always the props in the function signature, which most of the time is only the container object of your data, but not the data to be used, you can destructure the props early in the function signature.
One would call it React props destructuring:. As you have seen, props enable you to pass variables from one to another component down the component tree. In the previous example, it was only a string variable. But props can be anything from integers over objects to arrays. Even React components, but you will learn about this later. You can also define the props inline. In case of strings, you can pass props inside double quotes or single quotes too.
But you can also pass other data structures with inline props. In case of objects, it can be confusing for React beginners, because you have two curly braces: one for the JSX and one for the object. That's especially confusing when passing a style object to a style attribute in React the first time.
Note: It is important to note that is could lead to performance issues, because every time the component renders a new object is created again. But it can be a premature optimization as well when learning only about React.
Basically that's how props are passed to React components. As you may have noticed, props are only passed from top to bottom in React's component tree. There is no way to pass props up to a parent component.
Mock Function: Testing a React web app using Jest and Enzyme
We will revisit this issue later in this article. In addition, it's important to know that React's props are read only. There is no way in React to set props even though it was possible in the past.Simply doing jest.
Not sure why you need the extra mockComponent function but I'm very new to this too and might be missing something. That's a much better approach, damusnet! That's pretty much the exact functionality I was going for with my mockComponent and mockNamedComponents functions. Still wondering if there is an even more shorthand approach that would do this mocking behavior without having to manually define this boilerplate of an anonymous function each time.
TypeError: Cannot read property 'mockComponent' of undefinedI'm getting thisI checked the path of testUtils file as well. Skip to content. Instantly share code, notes, and snippets. Code Revisions 1 Stars 5 Forks 1. Embed What would you like to do? Embed Embed this gist in your website. Share Copy sharable link for this gist. Learn more about clone URLs. Download ZIP. Mocking children components with Jest - does this make sense?
First things first, create a react application using create-react-app. To get started with Enzyme, go ahead and install the library via yarn or npm as a dev dependency. Notice that we also installed an adapter alongside enzyme that matches the React version installed by create-react-app. You can read more about it in the Enzyme installation guide.
Shallow rendering is the most basic version of testing with Enzyme. As the name suggests, shallow rendering limits it's scope to the component to be tested and not it's children. Take a look at the List component below that expects an items prop and displays them in an unordered list.
The test suite imports a shallow enzyme method from the configuration we created in the previous section, wraps the List component and returns an instance of the rendered component. We then make a series of assertions against the instance to check if the component renders the content correctly. While the tests are not optimal, we take advantage of a few methods exposed by the shallow API. Sweet, right? In this section, we will look at full DOM rendering by making a few modifications to the component by breaking out the li element into a component of it's own called ListItem.
Let's now run the tests we wrote in the previous section and see what happens. If you did this right, your tests should be failing as terribly as mine are. Why would this happen? I mean the UI did not change at all.