ExUnit formatter that records every test outcome to the history file.

Add it alongside the default formatter in test/test_helper.exs:

ExUnit.start(formatters: [ExUnit.CLIFormatter, Temper.Formatter])

On :suite_started it gathers the run context (Temper.Env) and opens a Temper.History.Writer; each :test_finished appends one record; :suite_finished (or :sigquit/:max_failures_reached) appends a suite summary line and closes the file.

The history path defaults to .temper/history-{partition}.jsonl and can be overridden with the :history_path application env:

config :temper, history_path: "custom/history-{partition}.jsonl"

A literal {partition} in the configured path expands to the current MIX_TEST_PARTITION value ("0" when unset), keeping custom paths partition-safe the same way the default is. Without the placeholder, concurrent partitioned runs would all write to the same file.

Temper must never break a test run: every event handler is guarded — on any error the formatter logs a single warning and goes inert for the rest of the run.