Mock a dependency

Replace the real API client in this module with a mock so unit tests run offline. In the test, stub the fetchUser function to return a resolved promise with sample data, verify the component renders the sample user's name, and ensure the mock is restored after the test.

Before I submit the test changes, make the mock easier to review: keep the mocked shape identical to the real client, name the mock functions to match production names, surface failure modes (reject case) so reviewers see error handling, and avoid stubbing internal helper functions that make the mock brittle.

After adding a mock for the API client in one test file, other tests started receiving the stubbed responses and failing. I used a global module mock and I suspect teardown didn't restore it. I can't see where the leak originates. What is the likely cause and the safest change to isolate the mock to this test file only?

Over time we have many tests that mock modules differently; some use global module mocks, some replace require cache, and others monkey-patch. This inconsistency causes leaks and slow, confusing failures. Recommend one team-wide approach to mocking dependencies that minimizes leaks and makes tests easier to understand, and describe the single initial refactor to apply across the codebase.