Minor fixes (#8)

README.md

@@ -14,7 +14,7 @@ Add `:mutix` to your test dependencies in your `mix.exs` file:
 ```elixir
 def deps do
   [
-    {:mutix, git: "https://github.com/tuomohopia/mutix.git", tag: "v0.1.0", only: :test}
+    {:mutix, git: "https://github.com/tuomohopia/mutix.git", tag: "v0.1.0", only: [:dev, :test]}
   ]
 end
 ```

lib/mix/mutate.ex

@@ -83,7 +83,7 @@ defmodule Mix.Tasks.Mutate do
     if source_file_count == 0,
       do:
         Mix.raise(
-          "Please provide path to the source file to mutate, e.g. `mix mutate lib/my_app/transformer.ex`. Other options unsupported at this time."
+          "Please provide path to the source file to mutate, e.g. `mix mutate lib/my_app/transformer.ex`."
         )
 
     if source_file_count > 1,
@@ -96,7 +96,10 @@ defmodule Mix.Tasks.Mutate do
     end
 
     if Mix.Task.recursing?(), do: Mix.raise("Umbrella apps not supported yet.")
-    unless File.exists?(source_file), do: Mix.raise("Source module file must exist.")
+
+    unless File.exists?(source_file),
+      do: Mix.raise("Source module file #{source_file} does not exist.")
+
     _ = Mix.Project.get!()
     project = Mix.Project.config()
 
@@ -137,6 +140,10 @@ defmodule Mix.Tasks.Mutate do
     # One clean run first to assert all tests pass
     ExUnit.CaptureIO.with_io(fn ->
       case ExUnit.run() do
+        %{failures: 0, total: total, excluded: excluded, skipped: skipped}
+        when excluded + skipped == total ->
+          Mix.raise("No tests to run detected. Exited without running a mutation test suite.")
+
         %{failures: 0} ->
           :ok
 

lib/mutix/report.ex

@@ -15,7 +15,8 @@ defmodule Mutix.Report do
   def mutation(test_results, source_file_path, operator_mutation) do
     {from, to} = operator_mutation
     score = mutation_score(test_results)
-    percentage = score.survived_count / score.mutant_count * 100
+
+    percentage = (score.mutant_count - score.survived_count) / score.mutant_count * 100
     survived = score.survived
 
     survived_report =
@@ -32,7 +33,7 @@ defmodule Mutix.Report do
 
         #{score.killed_count} / #{score.mutant_count} mutants killed by the test suite.
 
-        Mutation score: #{percentage} %
+        Mutation score: #{Float.round(percentage, 1)} %
     #{survived_report}
     """
   end

test/mutix/report_test.exs

@@ -14,7 +14,7 @@ defmodule Mutix.ReportTest do
 
       0 / 1 mutants killed by the test suite.
 
-      Mutation score: 100.0 %
+      Mutation score: 0.0 %
 
   Surviving mutants (no test failed with these injections):
 
@@ -36,5 +36,21 @@ defmodule Mutix.ReportTest do
       result = Report.mutation(test_results, source_file_path, operator_mutation)
       assert result == String.replace_trailing(@single_operator_result, "\n\n\n", "\n\n")
     end
+
+    test "reports mutation score correctly" do
+      test_results = [
+        {%{total: 5, failures: 0, excluded: 0, skipped: 0}, [index_on_line: 0, line: 3], ""},
+        {%{total: 5, failures: 1, excluded: 0, skipped: 0}, [index_on_line: 0, line: 5], ""},
+        {%{total: 5, failures: 5, excluded: 0, skipped: 0}, [index_on_line: 0, line: 8], ""}
+      ]
+
+      source_file_path = "test/support/single_operator_source.ex"
+      operator_mutation = {:>, :<}
+
+      result = Report.mutation(test_results, source_file_path, operator_mutation)
+      assert result =~ "5 tests were run for each mutant."
+      assert result =~ "2 / 3 mutants killed by the test suite."
+      assert result =~ "Mutation score: 66.7 %"
+    end
   end
 end