In this folder (/test) you should only put integration tests that care equally about several modules, or tests that don't relate to any single module.

Example: The tests in node-version.test.js make sure that the node.js versions are consistent in tests, in the app and in the CI.

For unit tests, co-locate the test next to the module under test. Tests that are integration tests but have a clear main module under test could also be co-located.

Example: The tests in timer.test.js check that the module timer.js behaves correctly, and both files are located in the same folder (somewhere inside the src/ folder).