Add tests for fast fail through interrupts

spec/minitest_parallel_fork_interrupt_example.rb

@@ -0,0 +1,65 @@
+gem 'minitest'
+require 'minitest/global_expectations/autorun'
+require 'minitest/parallel_fork'
+require 'minitest/unit'
+require 'minitest/hooks/default' if ENV['MPF_MINITEST_HOOKS']
+
+ENV['NCPU'] = '4'
+
+# Taken and adapted from [Minitest.load_plugin](https://github.com/minitest/minitest/blob/6719ad8d8d49779669083f5029ea9a0429c49ff5/lib/minitest.rb#L108)
+#
+# We want to load plugins in spce/plugins and not in this Gem's lib/minitest
+# because:
+#
+#   1. the plugin doesn't belong to the library.
+#   2. the plugin doesn't behave as a proper plugin:
+#     a. we don't parse arguments and just load it
+#     b. we print to stdout and later on check the output for un/desired output
+module Minitest
+  def self.load_mpf_plugins
+    return unless self.extensions.empty?
+
+    seen = {}
+
+    Dir['spec/plugins/*_plugin.rb'].each do |plugin_path|
+      name = File.basename plugin_path, '_plugin.rb'
+
+      next if seen[name]
+      seen[name] = true
+
+      require_relative plugin_path.gsub(/\Aspec\//, '')
+      self.extensions << name
+    end
+  end
+end
+
+Minitest.load_mpf_plugins
+
+if ENV['MPF_FAIL_FAST']
+  class MyTest < MiniTest::Test
+    describe "failure through Interrupt" do
+      # We need to order the tests in order to verify the correct handling of
+      # the raised Interrupt by `Minitest.__run`.
+      # Unordered execution does not guarantee the number of un/executed tests,
+      # and assersions in `minitest_parallel_fork_spec.rb` would be impossible.
+      i_suck_and_my_tests_are_order_dependent!
+
+      parallelize_me! if ENV['MPF_PARALLELIZE_ME']
+
+      it "should fail" do
+        1.must_equal 2
+      end
+
+      it "should pass but will not" do
+        # We need to run a costly computation and not a `sleep`!
+        # Sleeping would not allow the runners to intercept the Interrupt or
+        # USR1 signals, and therefore we cannot reliably test for proper test
+        # abortion.
+        (1..1000000).inject(:*)
+        puts 'before must_equal'
+        1.must_equal 1
+        puts 'after must_equal'
+      end
+    end
+  end
+end

spec/minitest_parallel_fork_spec.rb

@@ -12,7 +12,9 @@
   def run_mpf(*env_keys)
     env_keys.each{|k| ENV[k] = '1'}
     t = Time.now
-    output = `#{ENV['RUBY']} -I lib spec/minitest_parallel_fork_example.rb 2>&1`
+    prefix = env_keys.include?('MPF_FAIL_FAST') ? 'interrupt_' : ''
+    example = "spec/minitest_parallel_fork_#{prefix}example.rb"
+    output = `#{ENV['RUBY']} -I lib #{example} 2>&1`
     [output, Time.now - t]
   ensure
     env_keys.each{|k| ENV.delete(k)}
@@ -63,4 +65,22 @@ def run_mpf(*env_keys)
     output.must_include '20 runs, 8 assertions, 4 failures, 8 errors, 4 skip'
     output.must_include 'Stats: 20R, 8A, 4F, 8E, 4S'
   end
+
+  it "should stop all serial executions when and Interrupt is raised" do
+    output, time = run_mpf('MPF_FAIL_FAST')
+    time.must_be :<, 1
+    output.must_include 'fast_fail_plugin loaded'
+    output.must_include '1 runs, 1 assertions, 1 failures, 0 errors, 0 skips'
+    output.wont_include 'before must_equal'
+    output.wont_include 'after must_equal'
+  end
+
+  it "should stop all parallel executions when and Interrupt is raised" do
+    output, time = run_mpf('MPF_FAIL_FAST', 'MPF_PARALLELIZE_ME')
+    time.must_be :<, 1
+    output.must_include 'fast_fail_plugin loaded'
+    output.must_include '1 runs, 1 assertions, 1 failures, 0 errors, 0 skips'
+    output.wont_include 'before must_equal'
+    output.wont_include 'after must_equal'
+  end
 end

spec/plugins/fail_fast_plugin.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require 'minitest'
+
+module Minitest
+  def self.plugin_fail_fast_options opts, _options
+    FailFastReporter.fail_fast!
+    puts 'fast_fail_plugin loaded'
+  end
+
+  def self.plugin_fail_fast_init options
+    if FailFastReporter.fail_fast?
+      io = options.fetch(:io, $stdout)
+      self.reporter.reporters << FailFastReporter.new(io, options)
+    end
+  end
+
+  class FailFastReporter < Reporter
+    def self.fail_fast!
+      @fail_fast = true
+    end
+
+    def self.fail_fast?
+      @fail_fast ||= false
+    end
+
+    def record result
+      if result.failures.reject { |failure| failure.is_a?(Minitest::Skip) }.any?
+        io.puts
+        raise Interrupt
+      else
+        super
+      end
+    end
+  end
+end