node --test started from inside a node:test run inherits NODE_TEST_CONTEXT and exits 0 even when its tests fail

Fact

The test runner sets NODE_TEST_CONTEXT in the environment of each test file's process. A node --test spawned from inside a test (or from code a test exercises) inherits it, takes itself for the runner's child, reports its results to a parent that is not listening, and exits 0 whether its tests pass or fail. Its printed output no longer says ✖ … fail N either.

Why it matters

Code that runs a project's tests as a gate — a CI helper, a bot that checks a change before opening a pull request — passes everything while under test, so its own tests prove nothing about the gate, and a test asserting "the failing suite is caught" fails in a confusing way (or passes for the wrong reason). Outside a test run the same code behaves correctly, which hides the cause.

How to apply

Drop the variable from the child's environment whenever spawning the runner:

const { NODE_TEST_CONTEXT, ...env } = process.env;
execFile(process.execPath, ['--test', file], { env });

Do it in the production code, not only in the test, so the gate is the same code in both places.