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

app/test/mutation_config_test.exs

@@ -0,0 +1,49 @@
+defmodule Firehose.MutationConfigTest do
+  # Same wiring pins as blogex, plus the app-specific one: because the app
+  # scope is deliberately empty (Q45), the aliases must fail loudly. A sensor
+  # that reports a score for a run that tested nothing is worse than no sensor.
+  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 "an empty app scope fails loudly instead of running over nothing" do
+    assert_raise Mix.Error, ~r/empty/, fn ->
+      Firehose.MixProject.mutation_args("mutation_scope.txt", [])
+    end
+  end
+
+  test "ad-hoc args do not bypass the empty-scope failure" do
+    assert_raise Mix.Error, ~r/empty/, fn ->
+      Firehose.MixProject.mutation_args("mutation_scope.txt", [
+        "--files",
+        "lib/firehose/accounts/user.ex"
+      ])
+    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
+end