The "test" folder often needs to contain files that are valid JavaScript but not valid tests (mocks, "karma.main.js"-kinda files, test-related helpers, etc).
Having something unique in the names of test files ('.spec.js', '.tap.js', etc) makes globbing much easier and keeps test-runner configuration simple.
It also makes it easier to apply different linting rules to different types of files independent of the folder they are in.
The "test" folder often needs to contain files that are valid JavaScript but not valid tests (mocks, "karma.main.js"-kinda files, test-related helpers, etc). Having something unique in the names of test files ('.spec.js', '.tap.js', etc) makes globbing much easier and keeps test-runner configuration simple. It also makes it easier to apply different linting rules to different types of files independent of the folder they are in.