Race conditions during process.env mutation in concurrent integration tests

Node.js provides the process.env global object to manage environment variables, and recent versions include the --env-file flag for native loading of configuration files. This mechanism is commonly used to swap production credentials for test-specific secrets during integration testing.

A challenge arises when asynchronous test suites attempt to mutate process.env at runtime to simulate different credential sets or environment states. Because process.env is a shared global object, concurrent tests may overwrite variables, leading to non-deterministic failures and flaky test results.

Technical Constraints

• The process.env object is shared across the entire Node.js process.
• Asynchronous test runners often execute tests in parallel within a single process.

What is the recommended pattern for isolating environment variables across concurrent tests without mutating the global process.env? Are there native alternatives to global mutation that maintain compatibility with --env-file?