Here are ten tips and tricks for writing great Jest unit tests for a React app:

1. Test component rendering: Ensure that your components render correctly by using the render function from the @testing-library/react package. Check if the expected elements are present in the rendered output.

2. Test component props: Verify that your components handle different props correctly. Pass various combinations of props to your components and assert that the expected behavior occurs.

3. Test event handlers: Simulate user interactions by using the fireEvent function from @testing-library/react. Trigger events like clicks, input changes, or form submissions and check if the corresponding event handlers are called and produce the expected results.

4. Use snapshots: Jest's snapshot testing feature allows you to capture the rendered output of a component and compare it against a stored snapshot. This helps detect unintended changes in the component's structure or styling.

5. Mock dependencies: When testing components that rely on external dependencies or modules, use Jest's mocking capabilities to create mock implementations. This allows you to control the behavior of the dependencies and focus on testing the component in isolation.

6. Test asynchronous behavior: If your components make asynchronous calls (e.g., API requests), use Jest's asynchronous testing utilities like async/await or done callback to handle and test the asynchronous behavior properly.

7. Test edge cases: Consider different edge cases and error scenarios when writing tests. Test how your components handle unexpected or invalid input, error states, and boundary conditions.

8. Use data-testid attribute: Add data-testid attributes to elements that you want to target in your tests. This provides a reliable way to select and interact with specific elements in your component without relying on class names or other brittle selectors.

9. Keep tests focused and independent: Each test should focus on a single behavior or scenario. Avoid testing multiple things in a single test. Also, ensure that tests are independent of each other and don't rely on the state or side effects of previous tests.

10. Use descriptive test names: Write clear and descriptive test names that convey the purpose and expected behavior of each test. This makes it easier to understand the test's intent and helps with debugging when tests fail.

Remember to also follow general best practices for writing tests, such as keeping tests small, readable, and maintainable. Regularly run your tests during development to catch any regressions or issues early on.