Jest ES module mock hoisting produces inconsistent test isolation

Mock Hoisting and ESM Interop

Likely Explanation

Jest's hoisting of jest.mock() occurs during the module transformation phase, preceding the actual ES module evaluation. However, import * as namespace creates a live binding to the module's namespace object. If the mock factory executes after this binding is established, the captured namespace bindings may retain references to the original, pre-mocked module exports, leading to inconsistent isolation across tests.

Confirmed Facts

• Mock state persists across test files because Jest shares the Node.js module cache unless explicitly cleared.
• jest.mock() factories run once per test file, not per test case.
• Native ESM evaluation order in Node dictates module instantiation before mock application timing can be reliably controlled without cache management.

Resolution Steps

1. Ensure jest.resetModules() is called in a global setup or within each test suite's beforeEach hook.
2. Verify your Jest configuration supports ESM correctly, noting differences between babel-jest transformation and native Node ESM environments.

Diagnostic Detail Needed

To confirm the root cause, please specify if the test suite runs under standard CommonJS transpilation (e.g., via ts-jest) or native Node ESM (e.g., package.json "type": "module").