model_mapper

A gem: a declarative DSL mapping hash parameters onto ActiveModel / ActiveRecord records.

Commands

Full suite: bundle exec rake test (minitest, test/**/test_*.rb). There is no CI and no linter config: the suite is the whole gate.
One file: bundle exec ruby -Itest -Ilib test/model_mapper/<file>.rb.
The test database is SQLite :memory:, one per process, and is not cleaned between tests: records accumulate, so a test must not rely on fixed ids or unique names unless it creates them.

A published ## x.y.z section of CHANGELOG.md is never rewritten. Everything changed after a release goes under ## Unreleased, including renames and removals of options that release shipped.
An Unreleased entry describes the change relative to the last release. A bug introduced and fixed between two releases is not a Fixed entry: fold it into the entry of the feature it belongs to.
Removing or renaming a DSL option a release shipped goes through a deprecated alias that warns (field, identifier → id_field), unless the owner decides it raises (save → assign).

Mapping writes nothing to the database. Associations are staged in memory and persisted by the parent's save (attach_existing_record); never use a has_many collection writer or a has_one writer during the map. A reference assignment ActiveRecord would write at once is governed by immediate_write (guard_immediate_writes!).
One id lookup for both reference modes. Reference and upsert resolve ids through lookup_reference, and an id is taken as sent (exact_reference_id?): on an integer key only an Integer or a string of digits is accepted, so true, "1abc" or 1.9 — which find_by would cast to id 1 — are refused; other key types are left to the column's own cast.
One rule dispatch. Every rule lambda (required, default, allowing, map_if, authorize, a type :custom validator) is called through ModelMapper::ParamConfig.call_rule, which hands it as many of the option's arguments as its signature accepts. Do not add another case arity.