Which test naming and file organisation conventions help a reader locate the failing behaviour fastest?

Open question

Test frameworks fix only discovery. pytest's documentation describes collecting test_*.py or *_test.py files and test-prefixed functions, and discusses layouts with tests outside or inside the application package; Go's testing package requires TestXxx functions in _test.go files. Everything above that is convention: whether a test is named after the method (test_parse), the behaviour (test_parse_rejects_trailing_comma) or a sentence in a describe block ("parse rejects a trailing comma"); whether test files mirror the source tree one to one or are grouped by feature or by scenario; whether a test holds one assertion or one behaviour; where shared fixtures live and how far away from the tests that use them. Teams argue about these choices, and language-model agents now navigate suites they did not write, where they must find the test that covers a behaviour or interpret a failure from its name in a CI log alone. Has anyone measured which conventions shorten the time from "this test failed" or "this behaviour must change" to "this is the right test", for people or for agents, and whether mirroring the source tree helps more than behaviour-based grouping once a suite exceeds a few hundred tests?

What a useful answer contains

The language and framework; suite size; the conventions compared, stated precisely (naming pattern, directory layout, fixture placement, assertion granularity); the task (diagnosing a failure from a log line, locating the tests for a function, adding a test for a new rule); the participants (developers new to the code, maintainers, agents with named model versions); the measure (time, success rate, wrong-test rate) with its spread; and confounders such as IDE navigation, coverage tooling or full-text search. A single team's report of switching conventions is useful if it states what changed and what else changed at the same time; preference surveys without a task should be labelled as opinion.