Actually we just need one runner

bin/test-mutations

@@ -2,4 +2,4 @@
 
 list=(`find spec -name '*_spec.cr' -and -not -name 'integration_spec.cr'`)
 printf '%s\n' "${list[@]}" | sort
-./bin/crytic test-parallel --min-msi=70.0 --reporters=Console,Stryker,ConsoleFileSummary "${list[@]}"
+./bin/crytic test --min-msi=70.0 --reporters=Console,Stryker,ConsoleFileSummary "${list[@]}"

bin/test-unit

@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-crystal spec -D skip-integration
+crystal spec -Dpreview-mt -D skip-integration

spec/integration_spec.cr

@@ -13,11 +13,10 @@ require "./spec_helper"
       end
     end
 
-    {% for command in ["test", "test-parallel"] %}
-    describe "the {{ command.id }} command" do
+    describe "the test command" do
       describe "--preamble/-p" do
         it "injects the given custom preamble, failing the neutral mutant" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr -p 'exit 1'")
+          result = run_crytic("test -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr -p 'exit 1'")
           result.output.should contain("unmodified subject")
           result.output.should_not contain("ConditionFlip")
           result.exit_code.should eq 1
@@ -26,7 +25,7 @@ require "./spec_helper"
 
       describe "with a fully covered subject" do
         it "passes the mutation specs" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/fully_covered_spec.cr")
+          result = run_crytic("test -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/fully_covered_spec.cr")
           result.output.should contain("✅ ConditionFlip")
           result.output.should contain("✅ BoolLiteralFlip")
           result.output.should contain("3 covered")
@@ -36,22 +35,22 @@ require "./spec_helper"
 
       describe "with an insufficiently covered subject" do
         it "fails the mutation specs" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr")
+          result = run_crytic("test -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr")
           result.output.should contain("❌ ConditionFlip")
           result.output.should contain("❌ BoolLiteralFlip")
           result.output.should contain("3 uncovered")
           result.exit_code.should be > 0
         end
 
         it "exits successfully when the msi threshold is set sufficiently" do
-          result = run_crytic("{{ command.id }} --min-msi=0.0 -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr")
+          result = run_crytic("test --min-msi=0.0 -s ./fixtures/conditionals/fully_covered.cr ./fixtures/conditionals/uncovered_spec.cr")
           result.exit_code.should eq 0
         end
       end
 
       describe "without passing a subject or tests" do
         it "mutates all sources and runs all tests" do
-          result = run_crytic_in_dir("./fixtures/autofind", {{ command }})
+          result = run_crytic_in_dir("./fixtures/autofind", "test")
           result.output.should contain("✅ ConditionFlip")
           result.output.should contain("✅ BoolLiteralFlip")
           result.output.should contain("✅ NumberLiteralSignFlip")
@@ -65,7 +64,7 @@ require "./spec_helper"
 
       describe "subject without any coverage" do
         it "fails all mutants" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/uncovered/without.cr ./fixtures/uncovered/without_spec.cr")
+          result = run_crytic("test -s ./fixtures/uncovered/without.cr ./fixtures/uncovered/without_spec.cr")
           result.output.should contain("❌ BoolLiteralFlip")
           result.output.should contain("❌ ConditionFlip")
           result.output.should contain("❌ NumberLiteralSignFlip")
@@ -77,7 +76,7 @@ require "./spec_helper"
 
       describe "a failing initial test suite" do
         it "reports initial failure" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/uncovered/without.cr ./fixtures/failing/failing_spec.cr")
+          result = run_crytic("test -s ./fixtures/uncovered/without.cr ./fixtures/failing/failing_spec.cr")
           result.output.should contain "❌ Original test suite failed.\n"
           result.output.should contain "no overload matches"
           result.exit_code.should be > 0
@@ -86,14 +85,13 @@ require "./spec_helper"
 
       describe "a subject that is mutated into an endless loop" do
         it "finishes and reports a timed out spec" do
-          result = run_crytic("{{ command.id }} -s ./fixtures/timeout/timeout.cr ./fixtures/timeout/timeout_spec.cr")
+          result = run_crytic("test -s ./fixtures/timeout/timeout.cr ./fixtures/timeout/timeout_spec.cr")
           result.output.should contain "✅ Original test suite passed.\n"
           result.output.should contain "1 timeout"
           result.exit_code.should be > 0
         end
       end
     end
-    {% end %}
 
     describe "the noop command" do
       it "outputs the noop'ed code to stdout" do

src/crytic/cli.cr

@@ -1,6 +1,5 @@
 require "./command/*"
 require "./runner/parallel"
-require "./runner/sequential"
 require "./side_effects"
 
 module Crytic
@@ -12,15 +11,13 @@ module Crytic
     def run(args)
       case args.first?
       when "test"
-        Command::Test.new(Runner::Sequential.new, @side_effects).execute(args.tap(&.shift))
-      when "test-parallel"
-        Command::Test.new(Runner::Parallel.new, @side_effects).execute(args.tap(&.shift))
+        Command::Test.new(@side_effects).execute(args.tap(&.shift))
       when "noop"
         Command::Noop
           .new(@side_effects, Command::Noop::DEFAULT_SPEC_FILES_GLOB)
           .execute(args.tap(&.shift))
       else
-        Command::Test.new(Runner::Sequential.new, @side_effects).execute(args)
+        Command::Test.new(@side_effects).execute(args)
       end
     end
   end

src/crytic/cli_options.cr

@@ -14,7 +14,6 @@ module Crytic
     @preamble = Generator::Generator::DEFAULT_PREAMBLE
     @spec_files = [] of String
     @subject = [] of String
-    getter multi_threaded : Bool = false
 
     def initialize(@side_effects : SideEffects, @spec_files_glob : String)
       @reporters << Reporter::IoReporter.new(@side_effects.std_out)

src/crytic/command/test.cr

@@ -2,13 +2,13 @@ require "../cli_options"
 require "../generator/in_memory_generator"
 require "../generator/isolated_mutation_factory"
 require "../mutation/no_mutation"
+require "../runner/parallel"
 require "../runner/run"
-require "../runner/runner"
 require "../side_effects"
 require "../subject"
 
 class Crytic::Command::Test
-  def initialize(@runner : Runner::Runner, @side_effects : SideEffects)
+  def initialize(@side_effects : SideEffects)
   end
 
   def execute(args)
@@ -18,7 +18,7 @@ class Crytic::Command::Test
       Mutation::NoMutation.with(specs)
     }
 
-    @runner.run(Crytic::Runner::Run.from_options(options, generator, factory), @side_effects)
+    Crytic::Runner::Parallel.run(Crytic::Runner::Run.from_options(options, generator, factory), @side_effects)
   end
 
   private def parse_options(args)

src/crytic/runner/parallel.cr

@@ -1,9 +1,8 @@
 require "../mutation/result_set"
-require "./runner"
 
 module Crytic::Runner
-  class Parallel < Runner
-    private SLICE_SIZE = 2
+  class Parallel
+    private SLICE_SIZE = 5
 
     def run(run, side_effects) : Bool
       original_result = run.execute_original_test_suite(side_effects)
@@ -28,22 +27,16 @@ module Crytic::Runner
       mutation_sets.each_slice(SLICE_SIZE) do |slice|
         channel = Channel(Array(Mutation::Result)).new(SLICE_SIZE)
 
-        slice.each_with_index do |set, idx|
-          STDOUT.puts "--- Mutant ##{idx}"
+        slice.each do |set|
           spawn do
-            STDOUT.puts "Run neutral mutant ##{idx}"
             neutral_result = set.run_neutral(run)
-            STDOUT.puts "Finished neutral mutant ##{idx}"
 
             if neutral_result.errored?
               channel.send(discard_further_mutations_for_single_subject)
             else
-              STDOUT.puts "Run mutant ##{idx}"
               channel.send(set.run_mutated(run))
-              STDOUT.puts "Finished mutant ##{idx}"
             end
           rescue exc
-            STDOUT.puts exc
             run.report_exception(exc)
             channel.send(discard_further_mutations_for_single_subject)
           end