![]() To learn more about this and see it in action, see this repo. For this reason, Jest will automatically hoist jest.mock calls to the top of the module (before any imports). But often you need to instruct Jest to use a mock before modules use it. If you're using ES module imports then you'll normally be inclined to put your import statements at the top of the test file. The code for this example is available at examples/manual-mocks. I have a node module which exports a few classes, one of which is Client, which I use to create a client (having a few APIs as methods). The require format goes like this: let config require ('config') And it takes the default export of config file. This ensures your tests will be fast and not flaky. After this, we can use the import statement to import them inside any other module. For this, we have to use the export keyword at the initial of the function declaration. For example, instead of accessing a remote resource like a website or a database, you might want to create a manual mock that allows you to use fake data. Export Function In TypeScript, we can export a function from the whole class. To ensure that a manual mock and its real implementation stay in sync, it might be useful to require the real module using jest.requireActual(moduleName) in your manual mock and amending it with mock functions before exporting it. 2 Answers Sorted by: 47 In ES6 you are allowed to export names using the export function, or for default you can export anything. Manual mocks are used to stub out functionality with mock data. ![]() Because of this, it's best to use or extend the automatic mock when it works for your needs. ![]() One downside to fully manual mocks is that they're manual – meaning you have to manually update them any time the module they are mocking changes. If you do not want to use the automatic mock at all, you can export your own functions from the mock file. This is the recommended approach, but is completely optional. Faker JS faker.js - generate massive amounts of fake data in the browser and node.js Marak / faker.js generate massive amounts of realistic fake data in Node.js and the browser faker.js - generate massive amounts of fake data in the browser and node. The example mock shown here uses jest.createMockFromModule to generate an automatic mock, and overrides its default behavior.
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