I'm learning both Jest and Cypress at same time. I know that they are not direct competitors because Cypress is focused on E2E and Jest on unit testing. For now I have implemented in my project both Jest and Cypress with few tests.
But actually most things I can test in both Cypress and Jest, and often I have hard time to decide with what write my test. Also it is harder to maintain compared to single test library.
I'm wondering - how often is Cypress (or alternative) and Jest (or alternative) used together? Is it really standard and good practice to use both? Or most developers/teams sticks with single one solution and it is fine?
short answers: It's very common to use Jest and Cypress in the same codebase.
Unit, Integration, or E2E tests
With component Libraries like Vue and React, the line between integration and unit tests can get a bit fuzzy. We can even use the same tools(Jest & Cypress)for both cases, which makes things even more confusing. I recommend that you aim to test "user stories" or, in other words, make sure that users can always perform key actions. For example:
Some of these tests will involve one component, others will involve two and some will require the entire application. I prefer writing smaller tests(unit and integration) using Jest and testing library because of the quick feedback loop. I get to develop and run my tests at, almost, the same time.
Eventually, you'll run into cases that involve so many moving parts(components) that using Jest is not an option. This is where Cypress shines, it's great for testing your end-to-end workflows.