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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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muex lib muex mutator arithmetic.ex
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lib/muex/mutator/arithmetic.ex 

defmodule Muex.Mutator.Arithmetic do

  @moduledoc """

  Mutator for arithmetic operators.



  Applies mutations to arithmetic operations:

  - `+` <-> `-`

  - `*` <-> `/`

  - `+` -> `0` (remove addition)

  - `-` -> `0` (remove subtraction)

  """

  @behaviour Muex.Mutator

  @impl true

  def name do

    "Arithmetic"

  end



  @impl true

  def description do

    "Mutates arithmetic operators (+, -, *, /)"

  end



  @impl true

  def mutate(ast, context) do

    case ast do

      {:+, meta, [left, right]} = original_ast ->

        line = Keyword.get(meta, :line, 0)



        [

          build_mutation(original_ast, {:-, meta, [left, right]}, "+ to -", context, line),

          build_mutation(original_ast, 0, "+ to 0 (remove)", context, line)

        ]



      {:-, meta, [left, right]} = original_ast ->

        line = Keyword.get(meta, :line, 0)



        [

          build_mutation(original_ast, {:+, meta, [left, right]}, "- to +", context, line),

          build_mutation(original_ast, 0, "- to 0 (remove)", context, line)

        ]



      {:*, meta, [left, right]} = original_ast ->

        line = Keyword.get(meta, :line, 0)



        [

          build_mutation(original_ast, {:/, meta, [left, right]}, "* to /", context, line),

          build_mutation(original_ast, 1, "* to 1 (identity)", context, line)

        ]



      {:/, meta, [left, right]} = original_ast ->

        line = Keyword.get(meta, :line, 0)



        [

          build_mutation(original_ast, {:*, meta, [left, right]}, "/ to *", context, line),

          build_mutation(original_ast, 1, "/ to 1 (identity)", context, line)

        ]



      _ ->

        []

    end

  end



  defp build_mutation(original_ast, mutated_ast, description, context, line) do

    %{

      original_ast: original_ast,

      ast: mutated_ast,

      mutator: __MODULE__,

      description: "#{name()}: #{description}",

      location: %{file: Map.get(context, :file, "unknown"), line: line}

    }

  end

end