# `Mutare.Test.RoutingExtension`
[🔗](https://github.com/foxbenjaminfox/mutare/blob/v0.2.1/lib/mutare/test/routing_extension.ex#L1)

A shipped routing-only extension for testing composition with foreign macro routing.

Libraries define how their macro arguments should be treated through `Mutare.CallRouting`. Use this fixture to test that your mutator respects routes registered by an independent module. It defines two inert pass-through macros and registers their argument routing:

| Macro | Route | Pins |
| --- | --- | --- |
| `opaque/1` | `:raw` | every argument is left as written — nothing inside the call is mutated |
| `tagged/2` | `[:expression, :raw]` | per-argument routing — the expression mutates, the label never does |

Both expand to their (first) argument, so fixtures using them still compile and run (`Mutare.Test.assert_metamutant_compiles/3`, `Mutare.Test.compile_metamutant/3`). Enable the routes by threading the module through the `Mutare.Test` helpers' `opts` — routing applies only when the extension is enabled, so the same source doubles as the unrouted contrast:

    import Mutare.Test
    alias Mutare.Test.RoutingExtension

    source = """
    defmodule M do
      import Mutare.Test.RoutingExtension
      def f(x), do: opaque(x + 1)
    end
    """

    # Unrouted, the argument mutates; routed, the foreign :raw suppresses it.
    assert {:arithmetic, "x + 1", "x - 1"} in diffs(source, [:arithmetic])
    assert diffs(source, [:arithmetic], extensions: [RoutingExtension]) == []

This is an extension — no `name/0`, no mutations — so it goes under `:extensions` (or a declarative `:call_routes` entry naming its macros, to test the config channel). It deliberately covers only the end-user treatments: the adapter-grade ones (`:interpolated`, `{:keyword, …}`, `:hosted`) assert facts about a real DSL's semantics that no generic fixture can stand in for — model those on the `Mutare.CallRouting` and `Mutare.Mutator.MacroHost` contracts against the library you're describing.

# `opaque`
*macro* 

Passes `expr` through unchanged. Routed fully `:raw` — its argument is opaque.

# `tagged`
*macro* 

Passes `expr` through, discarding `label`. Routed `[:expression, :raw]`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*