yak(mutation-testing-with-muex-blogex-pure-app-code-1341): mutation testing with muex (blogex + pure app code)

blogex/test/mutation_config_test.exs

@@ -0,0 +1,82 @@
+defmodule Blogex.MutationConfigTest do
+  # The mutation sensor is opt-in: a dependency and two aliases, deliberately
+  # absent from `make verify`'s VERIFY_SENSORS. These pins keep the wiring
+  # honest (dev/test only, never runtime) and keep the aliases reading the
+  # scope files rather than duplicating a list in mix.exs.
+  use ExUnit.Case
+
+  test "muex is a dev/test-only, non-runtime dependency" do
+    deps = Mix.Project.config()[:deps]
+
+    assert {:muex, requirement, opts} = dep!(deps, :muex)
+    assert requirement =~ "0.12"
+    assert opts[:only] == [:dev, :test]
+    assert opts[:runtime] == false
+  end
+
+  test "mutate and mutate.fast aliases are defined" do
+    aliases = Mix.Project.config()[:aliases]
+
+    assert is_function(aliases[:mutate], 1)
+    assert is_function(aliases[:"mutate.fast"], 1)
+  end
+
+  test "mutation args always include the scope, the curated mutators and --fail-at 0" do
+    args = Blogex.MixProject.mutation_args("mutation_scope_fast.txt", [])
+    scope = Blogex.MixProject.read_mutation_scope("mutation_scope_fast.txt")
+
+    assert "--fail-at" in args
+    assert Enum.at(args, Enum.find_index(args, &(&1 == "--fail-at")) + 1) == "0"
+    assert files_arg(args) == Enum.join(scope, ",")
+
+    mutators = Enum.at(args, Enum.find_index(args, &(&1 == "--mutators")) + 1)
+
+    assert mutators ==
+             "arithmetic,boolean,comparison,conditional,function_call,literal,return_value"
+  end
+
+  test "extra CLI args pass through so a single file can be targeted" do
+    args =
+      Blogex.MixProject.mutation_args("mutation_scope_fast.txt", ["--files", "lib/blogex/seo.ex"])
+
+    assert args
+           |> Enum.chunk_every(2, 1, :discard)
+           |> Enum.any?(fn
+             ["--files", "lib/blogex/seo.ex"] -> true
+             _ -> false
+           end)
+  end
+
+  test "an empty scope fails loudly instead of running over nothing" do
+    path =
+      Path.join(System.tmp_dir!(), "muex-empty-scope-#{System.unique_integer([:positive])}.txt")
+
+    File.write!(path, "\n   \n")
+    on_exit(fn -> File.rm(path) end)
+
+    assert_raise Mix.Error, ~r/empty/, fn ->
+      Blogex.MixProject.read_mutation_scope(path)
+    end
+  end
+
+  defp dep!(deps, name) do
+    case Enum.find(deps, fn
+           {^name, _requirement} -> true
+           {^name, _requirement, _opts} -> true
+           _ -> false
+         end) do
+      {^name, requirement} -> {name, requirement, []}
+      {^name, requirement, opts} -> {name, requirement, opts}
+      nil -> flunk("expected #{inspect(name)} in deps/0")
+    end
+  end
+
+  defp files_arg(args) do
+    args
+    |> Enum.chunk_every(2, 1, :discard)
+    |> Enum.find_value(fn
+      ["--files", files] -> files
+      _ -> nil
+    end)
+  end
+end