mostlyobvious · mostlyobvious · Apr 30, 2026 · Apr 30, 2026 · Apr 30, 2026
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
@@ -29,3 +29,5 @@ jobs:
           bundler-cache: true
       - name: Run the default task
         run: bin/rake
+      - name: Full mutant run
+        run: bin/mutant run
diff --git a/.mutant.yml b/.mutant.yml
@@ -8,7 +8,7 @@ requires:
 - connection_pool
 - en57
 integration:
-  name: minitest
+  name: tldr
 matcher:
   subjects:
     - En57*

diff --git a/.tldr.yml b/.tldr.yml
@@ -0,0 +1,2 @@
+helper_paths:
+  - test/test_helper.rb
diff --git a/Gemfile b/Gemfile
@@ -7,11 +7,11 @@ gemspec
 gem "bigdecimal"
 gem "irb"
 gem "rake"
-gem "m"
-gem "minitest"
 gem "minitest-mock"
-gem "mutant-minitest"
 gem "concurrent-ruby"
+gem "tldr"
+gem "mutant", github: "mostlyobvious/mutant"
+gem "mutant-tldr", github: "mostlyobvious/mutant"
 gem "pg-ephemeral"
 gem "syntax_tree"
 

diff --git a/Gemfile.lock b/Gemfile.lock
@@ -1,3 +1,19 @@
+GIT
+  remote: https://github.com/mostlyobvious/mutant.git
+  revision: f6b6f88a0c766916a2c221892ae00e397810d83f
+  specs:
+    mutant (0.16.2)
+      diff-lcs (>= 1.6, < 3)
+      irb (~> 1.15)
+      parser (~> 3.3.10)
+      regexp_parser (~> 2.10)
+      securerandom (>= 0.3)
+      sorbet-runtime (~> 0.6.0)
+      unparser (>= 0.8.2, < 0.10)
+    mutant-tldr (0.16.2)
+      mutant (= 0.16.2)
+      tldr (~> 1.0)
+
 PATH
   remote: .
   specs:
@@ -27,6 +43,7 @@ GEM
       tzinfo (~> 2.0, >= 2.0.5)
       uri (>= 0.13.1)
     ast (2.4.3)
+    attr_extras (7.1.0)
     base64 (0.3.0)
     bigdecimal (4.1.2)
     concurrent-ruby (1.3.6)
@@ -45,28 +62,16 @@ GEM
       reline (>= 0.4.2)
     json (2.19.4)
     logger (1.7.0)
-    m (1.7.0)
-      rake
     minitest (6.0.5)
       drb (~> 2.0)
       prism (~> 1.5)
     minitest-mock (5.27.0)
-    mutant (0.16.2)
-      diff-lcs (>= 1.6, < 3)
-      irb (~> 1.15)
-      parser (~> 3.3.10)
-      regexp_parser (~> 2.10)
-      securerandom (>= 0.3)
-      sorbet-runtime (~> 0.6.0)
-      unparser (>= 0.8.2, < 0.10)
-    mutant-minitest (0.16.2)
-      minitest (>= 5.11, < 7)
-      mutant (= 0.16.2)
-      mutex_m (~> 0.2)
-    mutex_m (0.3.0)
+    optimist (3.2.1)
     parser (3.3.11.1)
       ast (~> 2.4.1)
       racc
+    patience_diff (1.2.0)
+      optimist (~> 3.0)
     pg (1.6.3)
     pg (1.6.3-aarch64-linux)
     pg (1.6.3-arm64-darwin)
@@ -99,9 +104,17 @@ GEM
       bigdecimal
     sorbet-runtime (0.6.13169)
     stringio (3.2.0)
+    super_diff (0.18.0)
+      attr_extras (>= 6.2.4)
+      diff-lcs
+      patience_diff
     syntax_tree (6.3.0)
       prettier_print (>= 1.2.0)
     timeout (0.6.1)
+    tldr (1.1.1)
+      concurrent-ruby (~> 1.2)
+      irb (~> 1.10)
+      super_diff (~> 0.10)
     tsort (0.2.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
@@ -123,20 +136,21 @@ DEPENDENCIES
   connection_pool
   en57!
   irb
-  m
-  minitest
   minitest-mock
-  mutant-minitest
+  mutant!
+  mutant-tldr!
   pg-ephemeral
   rake
   sequel
   syntax_tree
+  tldr
 
 CHECKSUMS
   activemodel (8.1.3) sha256=90c05cbe4cef3649b8f79f13016191ea94c4525ce4a5c0fb7ef909c4b91c8219
   activerecord (8.1.3) sha256=8003be7b2466ba0a2a670e603eeb0a61dd66058fccecfc49901e775260ac70ab
   activesupport (8.1.3) sha256=21a5e0dfbd4c3ddd9e1317ec6a4d782fa226e7867dc70b0743acda81a1dca20e
   ast (2.4.3) sha256=954615157c1d6a382bc27d690d973195e79db7f55e9765ac7c481c60bdb4d383
+  attr_extras (7.1.0) sha256=d96fc9a9dd5d85ba2d37762440a816f840093959ae26bb90da994c2d9f1fc827
   base64 (0.3.0) sha256=27337aeabad6ffae05c265c450490628ef3ebd4b67be58257393227588f5a97b
   bigdecimal (4.1.2) sha256=53d217666027eab4280346fba98e7d5b66baaae1b9c3c1c0ffe89d48188a3fbd
   bundler (4.0.11) sha256=5bcec0fb78302e48d02ee46f10ee6e6942be647ba5b44a6d1ddfda9a240ce785
@@ -152,13 +166,13 @@ CHECKSUMS
   irb (1.18.0) sha256=de9454a0703a54704b9811a5ef31a60c86949fbf4013fcf244fabc7c775248e3
   json (2.19.4) sha256=670a7d333fb3b18ca5b29cb255eb7bef099e40d88c02c80bd42a3f30fe5239ac
   logger (1.7.0) sha256=196edec7cc44b66cfb40f9755ce11b392f21f7967696af15d274dde7edff0203
-  m (1.7.0) sha256=058f793da8150c51353cc59366ffae7774683e868bede3c78f81d920fb9d633a
   minitest (6.0.5) sha256=f007d7246bf4feea549502842cd7c6aba8851cdc9c90ba06de9c476c0d01155c
   minitest-mock (5.27.0) sha256=7040ed7185417a966920987eaa6eaf1be4ea1fc5b25bb03ff4703f98564a55b0
-  mutant (0.16.2) sha256=0e9678652093d9fa134f7828f7cdce2b19e322370b2f184f7dcdacf1b70f38e5
-  mutant-minitest (0.16.2) sha256=041c51cd75b7bd649c4ef3b530f5f329ca8470ece76714143c8520af31606c47
-  mutex_m (0.3.0) sha256=cfcb04ac16b69c4813777022fdceda24e9f798e48092a2b817eb4c0a782b0751
+  mutant (0.16.2)
+  mutant-tldr (0.16.2)
+  optimist (3.2.1) sha256=8cf8a0fd69f3aa24ab48885d3a666717c27bc3d9edd6e976e18b9d771e72e34e
   parser (3.3.11.1) sha256=d17ace7aabe3e72c3cc94043714be27cc6f852f104d81aa284c2281aecc65d54
+  patience_diff (1.2.0) sha256=f492094486af02fff4a80070fa6b4d0ebbcf4d42fb38bba29d095eef43f6822c
   pg (1.6.3) sha256=1388d0563e13d2758c1089e35e973a3249e955c659592d10e5b77c468f628a99
   pg (1.6.3-aarch64-linux) sha256=0698ad563e02383c27510b76bf7d4cd2de19cd1d16a5013f375dd473e4be72ea
   pg (1.6.3-arm64-darwin) sha256=7240330b572e6355d7c75a7de535edb5dfcbd6295d9c7777df4d9dddfb8c0e5f
@@ -180,8 +194,10 @@ CHECKSUMS
   sequel (5.103.0) sha256=51bf23374cc585724fc51a2ae8b95283422c97ca4585ce28f3db27a26ce55a69
   sorbet-runtime (0.6.13169) sha256=6c520bc1ba75d9d982003d957548ec8a941dfa3c3342322a2db20bc28f174b3e
   stringio (3.2.0) sha256=c37cb2e58b4ffbd33fe5cd948c05934af997b36e0b6ca6fdf43afa234cf222e1
+  super_diff (0.18.0) sha256=9f5e77464fa75150619f7783174fbbe1bbac50a1eaf157cd39ad5584b0eac142
   syntax_tree (6.3.0) sha256=56e25a9692c798ec94c5442fe94c5e94af76bef91edc8bb02052cbdecf35f13d
   timeout (0.6.1) sha256=78f57368a7e7bbadec56971f78a3f5ecbcfb59b7fcbb0a3ed6ddc08a5094accb
+  tldr (1.1.1) sha256=fbf6386d9689eee1f18fe2bd5b565bff2b19832dc22fdb02e7acddca220edf8c
   tsort (0.2.0) sha256=9650a793f6859a43b6641671278f79cfead60ac714148aabe4e3f0060480089f
   tzinfo (2.0.6) sha256=8daf828cc77bcf7d63b0e3bdb6caa47e2272dcfaf4fbfe46f8c3a9df087a829b
   unparser (0.9.0) sha256=4331f174a73a23b69250b13d47da3794ed1449711ee0f9ed8947dc020ba76067

diff --git a/Rakefile b/Rakefile
@@ -2,11 +2,12 @@
 
 require "bundler/gem_tasks"
 require "fileutils"
-require "minitest/test_task"
+require "tldr/rake"
 require "uri"
 require_relative "lib/en57/tasks"
 
-Minitest::TestTask.create
+desc "Run tests"
+task test: :tldr
 
 def pg_regress_bin
   candidates = [

diff --git a/bin/m → bin/tldr b/bin/m → bin/tldr
@@ -4,7 +4,7 @@
 #
 # This file was generated by Bundler.
 #
-# The application 'm' is installed as part of a gem, and
+# The application 'tldr' is installed as part of a gem, and
 # this file is here to facilitate running it.
 #
 
@@ -13,4 +13,4 @@ ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
 require "rubygems"
 require "bundler/setup"
 
-load Gem.bin_path("m", "m")
+load Gem.bin_path("tldr", "tldr")
diff --git a/bin/tldt b/bin/tldt
@@ -0,0 +1,16 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+#
+# This file was generated by Bundler.
+#
+# The application 'tldt' is installed as part of a gem, and
+# this file is here to facilitate running it.
+#
+
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+require "rubygems"
+require "bundler/setup"
+
+load Gem.bin_path("tldr", "tldt")
diff --git a/test/test_active_record_adapter.rb b/test/test_active_record_adapter.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestActiveRecordAdapter < Minitest::Test
+  class TestActiveRecordAdapter < TLDR
     cover ActiveRecordAdapter
 
     def test_with_connection_checks_out_connection_and_yields_raw_connection

diff --git a/test/test_en57.rb b/test/test_en57.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestEn57 < Minitest::Test
+  class TestEn57 < TLDR
     cover En57
 
     def test_that_it_has_a_version_number

diff --git a/test/test_event.rb b/test/test_event.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestEvent < Minitest::Test
+  class TestEvent < TLDR
     cover Event
 
     def test_generates_uuid_v7_by_default

diff --git a/test/test_event_store.rb b/test/test_event_store.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestEventStore < Minitest::Test
+  class TestEventStore < TLDR
     cover EventStore
 
     def test_append_event

diff --git a/test/test_factories.rb b/test/test_factories.rb
@@ -4,6 +4,8 @@
 
 module En57
   class TestFactories < IntegrationTest
+    TLDR.dont_run_these_in_parallel!
+
     def test_for_pg_round_trips_with_connection_uri
       assert_round_trip EventStore.for_pg(SERVER.url)
     end

diff --git a/test/test_helper.rb b/test/test_helper.rb
@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
-require "minitest/autorun"
+require "tldr/autorun"
 require "minitest/mock"
-require "mutant/minitest/coverage"
+require "mutant/tldr/coverage"
 
 # optional dependencies
 require "sequel"
@@ -17,7 +17,7 @@
 require "pg_ephemeral"
 
 module En57
-  class IntegrationTest < Minitest::Test
+  class IntegrationTest < TLDR
     SERVER = PgEphemeral.start
 
     CONNECTION = PG.connect(SERVER.url)
@@ -49,12 +49,15 @@ def setup =
         "TRUNCATE TABLE en57.tags, en57.events RESTART IDENTITY CASCADE",
       )
 
-    Minitest.after_run do
+    at_exit do
       AR_POOL.disconnect!
       SEQUEL_DB.disconnect
       PG_POOL.shutdown(&:close)
       CONNECTION.close
-      SERVER.shutdown
+      begin
+        SERVER.shutdown
+      rescue Errno::ECHILD
+      end
     end
   end
 end
diff --git a/test/test_integration.rb b/test/test_integration.rb
@@ -4,6 +4,8 @@
 
 module En57
   class TestIntegration < IntegrationTest
+    TLDR.dont_run_these_in_parallel!
+
     ADAPTERS.each do |name, factory|
       define_method "test_#{name}_happy_path" do
         with_event_store(factory) do |event_store|

diff --git a/test/test_json_serializer.rb b/test/test_json_serializer.rb
@@ -8,7 +8,7 @@
 require "openssl"
 
 module En57
-  class TestJsonSerializer < Minitest::Test
+  class TestJsonSerializer < TLDR
     cover JsonSerializer
 
     class Example < Data.define(:name, :value, :serialized, :klass)

diff --git a/test/test_migrator.rb b/test/test_migrator.rb
@@ -5,6 +5,8 @@
 
 module En57
   class TestMigrator < IntegrationTest
+    TLDR.dont_run_these_in_parallel!
+
     def test_status_reports_pending_schema_on_empty_database
       with_database do |url|
         assert_equal(

diff --git a/test/test_pg_adapter.rb b/test/test_pg_adapter.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestPgAdapter < Minitest::Test
+  class TestPgAdapter < TLDR
     cover PgAdapter
 
     def test_with_connection_yields_connection

diff --git a/test/test_query.rb b/test/test_query.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestQuery < Minitest::Test
+  class TestQuery < TLDR
     cover Query
 
     def test_refine_last_starts_from_all_item

diff --git a/test/test_repository.rb b/test/test_repository.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestRepository < Minitest::Test
+  class TestRepository < TLDR
     cover Repository
 
     def test_append_wraps_write_in_serializable_transaction

diff --git a/test/test_scope.rb b/test/test_scope.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestScope < Minitest::Test
+  class TestScope < TLDR
     cover Scope
 
     def test_empty_scope_returns_query_all

diff --git a/test/test_sequel_adapter.rb b/test/test_sequel_adapter.rb
@@ -3,7 +3,7 @@
 require "test_helper"
 
 module En57
-  class TestSequelAdapter < Minitest::Test
+  class TestSequelAdapter < TLDR
     cover SequelAdapter
 
     def test_with_connection_synchronizes_and_yields_connection

diff --git a/test/test_stress.rb b/test/test_stress.rb
@@ -4,6 +4,8 @@
 
 module En57
   class TestStress < IntegrationTest
+    TLDR.dont_run_these_in_parallel!
+
     ADAPTERS.each do |name, factory|
       define_method(
         "test_#{name}_only_one_writer_can_consume_account_credits",