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Language-agnostic mutation testing library for Elixir, Erlang, and other BEAM languages. Evaluates test suite quality by introducing deliberate bugs into code and verifying that tests catch them. Intelligent file filtering, 18 mutation strategies, sound equivalent-mutant handling, and more.
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lib/muex/mutator/map_semantics.ex
defmodule Muex.Mutator.MapSemantics do
@moduledoc """
Elixir-specific mutator that swaps `put`/`put_new` on `Map` and `Keyword`.
- `Map.put` <-> `Map.put_new`
- `Keyword.put` <-> `Keyword.put_new`
`put` always writes; `put_new` writes only when the key is absent. They have
the same arity and return type, so a surviving mutant means no test exercises
the case where the key is already present — a common real-world bug.
Only module-qualified calls on `Map`/`Keyword` are matched; the call
arguments are preserved.
"""
@behaviour Muex.Mutator
alias Muex.Mutator.Builders
@opposites %{put: :put_new, put_new: :put}
@modules [:Map, :Keyword]
@impl true
def name, do: "MapSemantics"
@impl true
def description, do: "Swaps Map/Keyword put for put_new"
@impl true
def supported_languages, do: [Muex.Language.Elixir]
@impl true
def mutate(ast, context),
do: Builders.module_fn_swap(ast, context, __MODULE__, @modules, @opposites)
end