Write down what the green tests taught this cycle

hosting-panels/common/tests/README.md

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+# Tests
+
+Run one: `bash hosting-panels/common/tests/test_queue.sh`.
+CI runs all of them on every pull request, and fails if a test here has no step
+in `.github/workflows/tests.yml`.
+
+These are integration scripts for panels we cannot run in CI, so most of them
+extract the function under test out of the installer or hook and drive it
+directly. That is deliberate: a test that greps the source describes it, a test
+that runs it can be wrong about it.
+
+## Three rules, each learned from a green test over broken code
+
+### A word being present is not a criterion
+
+Assert the property, not the mention.
+
+`test_pdns_restart.sh` first checked that `pgrep -x pdns_server` appeared in the
+installer. It does — in the *backend detection*, ten lines above. Removing the
+liveness check after the restart left the test green.
+
+`test_named_conf_edit.sh` first checked that `named-checkconf` appeared. It
+does — in the message `"Check: named-checkconf"`. Replacing the actual guard
+with `if true` left the test green.
+
+Both now assert what the code does: `if named-checkconf` gating the branch, a
+rollback line restoring the backup, a `did not come back` message on the path
+where the service stayed down.
+
+### GNU extensions break silently on BSD
+
+`sed -i` without an argument, `\?`, `i\` with a leading tab — all GNU-only. On
+macOS they do not error; they produce different output. The old `named.conf`
+edit yielded `talso-notify` there and left a quoted `"none"` in place, on a
+machine where nobody was looking.
+
+Prefer POSIX: `sed 'script' file > tmp && cat tmp > file`, `awk` for inserts,
+character classes over `\?`. A test that *runs* the code catches this. A test
+that greps it cannot.
+
+### Give every enumeration a lower bound
+
+A check that walks a list must fail when the list comes back empty, not pass.
+
+`TestEveryHandlerRendersHTML` looked for `sendEmail` and found 15 handlers; the
+bound of 18 caught that three more send through `sendEmailNoArchive` and were
+being skipped. `test_pdns_restart.sh` and `test_named_conf_edit.sh` carry
+`checked >= 3` for the same reason: a rename that stops matching the installers
+has to be red, not quietly green over nothing.
+
+## Fixtures
+
+`fixtures/cpanel-named.conf` is a real `named.conf` from a cPanel 136 server —
+three views and a logging block. It is the shape that broke: an insert bounded
+only by `};` lands inside logging and named stops parsing the file. Keep it as
+it came off the server; a simplified copy would stop reproducing the failure.