diff --git a/test/lib/core_assertions.rb b/test/lib/core_assertions.rb
new file mode 100644
index 0000000..6e564c9
--- /dev/null
+++ b/test/lib/core_assertions.rb
@@ -0,0 +1,314 @@
+# frozen_string_literal: true
+
+module Test
+  module Unit
+    module CoreAssertions
+      if defined?(MiniTest)
+        require_relative '../../envutil'
+        # for ruby core testing
+        include MiniTest::Assertions
+      else
+        require 'pp'
+        require_relative 'envutil'
+        include Test::Unit::Assertions
+
+        def _assertions= n # :nodoc:
+          @_assertions = n
+        end
+
+        def _assertions # :nodoc:
+          @_assertions ||= 0
+        end
+
+        ##
+        # Returns a proc that will output +msg+ along with the default message.
+
+        def message msg = nil, ending = nil, &default
+          proc {
+            msg = msg.call.chomp(".") if Proc === msg
+            custom_message = "#{msg}.\n" unless msg.nil? or msg.to_s.empty?
+            "#{custom_message}#{default.call}#{ending || "."}"
+          }
+        end
+      end
+
+      def mu_pp(obj) #:nodoc:
+        obj.pretty_inspect.chomp
+      end
+
+      def assert_file
+        AssertFile
+      end
+
+      FailDesc = proc do |status, message = "", out = ""|
+        now = Time.now
+        proc do
+          EnvUtil.failure_description(status, now, message, out)
+        end
+      end
+
+      def assert_in_out_err(args, test_stdin = "", test_stdout = [], test_stderr = [], message = nil,
+                            success: nil, **opt)
+        args = Array(args).dup
+        args.insert((Hash === args[0] ? 1 : 0), '--disable=gems')
+        stdout, stderr, status = EnvUtil.invoke_ruby(args, test_stdin, true, true, **opt)
+        desc = FailDesc[status, message, stderr]
+        if block_given?
+          raise "test_stdout ignored, use block only or without block" if test_stdout != []
+          raise "test_stderr ignored, use block only or without block" if test_stderr != []
+          yield(stdout.lines.map {|l| l.chomp }, stderr.lines.map {|l| l.chomp }, status)
+        else
+          all_assertions(desc) do |a|
+            [["stdout", test_stdout, stdout], ["stderr", test_stderr, stderr]].each do |key, exp, act|
+              a.for(key) do
+                if exp.is_a?(Regexp)
+                  assert_match(exp, act)
+                elsif exp.all? {|e| String === e}
+                  assert_equal(exp, act.lines.map {|l| l.chomp })
+                else
+                  assert_pattern_list(exp, act)
+                end
+              end
+            end
+            unless success.nil?
+              a.for("success?") do
+                if success
+                  assert_predicate(status, :success?)
+                else
+                  assert_not_predicate(status, :success?)
+                end
+              end
+            end
+          end
+          status
+        end
+      end
+
+      def assert_ruby_status(args, test_stdin="", message=nil, **opt)
+        out, _, status = EnvUtil.invoke_ruby(args, test_stdin, true, :merge_to_stdout, **opt)
+        desc = FailDesc[status, message, out]
+        assert(!status.signaled?, desc)
+        message ||= "ruby exit status is not success:"
+        assert(status.success?, desc)
+      end
+
+      ABORT_SIGNALS = Signal.list.values_at(*%w"ILL ABRT BUS SEGV TERM")
+
+      def assert_separately(args, file = nil, line = nil, src, ignore_stderr: nil, **opt)
+        unless file and line
+          loc, = caller_locations(1,1)
+          file ||= loc.path
+          line ||= loc.lineno
+        end
+        src = <<eom
+# -*- coding: #{line += __LINE__; src.encoding}; -*-
+  require "test/unit";include Test::Unit::Assertions;require #{(__dir__ + "/core_assertions").dump};include Test::Unit::CoreAssertions
+  END {
+    puts [Marshal.dump($!)].pack('m'), "assertions=\#{self._assertions}"
+  }
+#{line -= __LINE__; src}
+  class Test::Unit::Runner
+    @@stop_auto_run = true
+  end
+eom
+        args = args.dup
+        args.insert((Hash === args.first ? 1 : 0), "-w", "--disable=gems", *$:.map {|l| "-I#{l}"})
+        stdout, stderr, status = EnvUtil.invoke_ruby(args, src, true, true, **opt)
+        abort = status.coredump? || (status.signaled? && ABORT_SIGNALS.include?(status.termsig))
+        assert(!abort, FailDesc[status, nil, stderr])
+        self._assertions += stdout[/^assertions=(\d+)/, 1].to_i
+        begin
+          res = Marshal.load(stdout.unpack("m")[0])
+        rescue => marshal_error
+          ignore_stderr = nil
+        end
+        if res
+          if bt = res.backtrace
+            bt.each do |l|
+              l.sub!(/\A-:(\d+)/){"#{file}:#{line + $1.to_i}"}
+            end
+            bt.concat(caller)
+          else
+            res.set_backtrace(caller)
+          end
+          raise res unless SystemExit === res
+        end
+
+        # really is it succeed?
+        unless ignore_stderr
+          # the body of assert_separately must not output anything to detect error
+          assert(stderr.empty?, FailDesc[status, "assert_separately failed with error message", stderr])
+        end
+        assert(status.success?, FailDesc[status, "assert_separately failed", stderr])
+        raise marshal_error if marshal_error
+      end
+
+      # :call-seq:
+      #   assert_throw( tag, failure_message = nil, &block )
+      #
+      #Fails unless the given block throws +tag+, returns the caught
+      #value otherwise.
+      #
+      #An optional failure message may be provided as the final argument.
+      #
+      #    tag = Object.new
+      #    assert_throw(tag, "#{tag} was not thrown!") do
+      #      throw tag
+      #    end
+      def assert_throw(tag, msg = nil)
+        ret = catch(tag) do
+          begin
+            yield(tag)
+          rescue UncaughtThrowError => e
+            thrown = e.tag
+          end
+          msg = message(msg) {
+            "Expected #{mu_pp(tag)} to have been thrown"\
+            "#{%Q[, not #{thrown}] if thrown}"
+          }
+          assert(false, msg)
+        end
+        assert(true)
+        ret
+      end
+
+      # :call-seq:
+      #   assert_raise_with_message(exception, expected, msg = nil, &block)
+      #
+      #Tests if the given block raises an exception with the expected
+      #message.
+      #
+      #    assert_raise_with_message(RuntimeError, "foo") do
+      #      nil #Fails, no Exceptions are raised
+      #    end
+      #
+      #    assert_raise_with_message(RuntimeError, "foo") do
+      #      raise ArgumentError, "foo" #Fails, different Exception is raised
+      #    end
+      #
+      #    assert_raise_with_message(RuntimeError, "foo") do
+      #      raise "bar" #Fails, RuntimeError is raised but the message differs
+      #    end
+      #
+      #    assert_raise_with_message(RuntimeError, "foo") do
+      #      raise "foo" #Raises RuntimeError with the message, so assertion succeeds
+      #    end
+      def assert_raise_with_message(exception, expected, msg = nil, &block)
+        case expected
+        when String
+          assert = :assert_equal
+        when Regexp
+          assert = :assert_match
+        else
+          raise TypeError, "Expected #{expected.inspect} to be a kind of String or Regexp, not #{expected.class}"
+        end
+
+        ex = m = nil
+        EnvUtil.with_default_internal(expected.encoding) do
+          ex = assert_raise(exception, msg || proc {"Exception(#{exception}) with message matches to #{expected.inspect}"}) do
+            yield
+          end
+          m = ex.message
+        end
+        msg = message(msg, "") {"Expected Exception(#{exception}) was raised, but the message doesn't match"}
+
+        if assert == :assert_equal
+          assert_equal(expected, m, msg)
+        else
+          msg = message(msg) { "Expected #{mu_pp expected} to match #{mu_pp m}" }
+          assert expected =~ m, msg
+          block.binding.eval("proc{|_|$~=_}").call($~)
+        end
+        ex
+      end
+
+      def assert_warning(pat, msg = nil)
+        result = nil
+        stderr = EnvUtil.with_default_internal(pat.encoding) {
+          EnvUtil.verbose_warning {
+            result = yield
+          }
+        }
+        msg = message(msg) {diff pat, stderr}
+        assert(pat === stderr, msg)
+        result
+      end
+
+      def assert_warn(*args)
+        assert_warning(*args) {$VERBOSE = false; yield}
+      end
+
+      class << (AssertFile = Struct.new(:failure_message).new)
+        include CoreAssertions
+        def assert_file_predicate(predicate, *args)
+          if /\Anot_/ =~ predicate
+            predicate = $'
+            neg = " not"
+          end
+          result = File.__send__(predicate, *args)
+          result = !result if neg
+          mesg = "Expected file ".dup << args.shift.inspect
+          mesg << "#{neg} to be #{predicate}"
+          mesg << mu_pp(args).sub(/\A\[(.*)\]\z/m, '(\1)') unless args.empty?
+          mesg << " #{failure_message}" if failure_message
+          assert(result, mesg)
+        end
+        alias method_missing assert_file_predicate
+
+        def for(message)
+          clone.tap {|a| a.failure_message = message}
+        end
+      end
+
+      class AllFailures
+        attr_reader :failures
+
+        def initialize
+          @count = 0
+          @failures = {}
+        end
+
+        def for(key)
+          @count += 1
+          yield
+        rescue Exception => e
+          @failures[key] = [@count, e]
+        end
+
+        def foreach(*keys)
+          keys.each do |key|
+            @count += 1
+            begin
+              yield key
+            rescue Exception => e
+              @failures[key] = [@count, e]
+            end
+          end
+        end
+
+        def message
+          i = 0
+          total = @count.to_s
+          fmt = "%#{total.size}d"
+          @failures.map {|k, (n, v)|
+            v = v.message
+            "\n#{i+=1}. [#{fmt%n}/#{total}] Assertion for #{k.inspect}\n#{v.b.gsub(/^/, '   | ').force_encoding(v.encoding)}"
+          }.join("\n")
+        end
+
+        def pass?
+          @failures.empty?
+        end
+      end
+
+      def assert_all_assertions(msg = nil)
+        all = AllFailures.new
+        yield all
+      ensure
+        assert(all.pass?, message(msg) {all.message.chomp(".")})
+      end
+      alias all_assertions assert_all_assertions
+
+    end
+  end
+end
diff --git a/test/lib/envutil.rb b/test/lib/envutil.rb
index b4eb63d..2faf483 100644
--- a/test/lib/envutil.rb
+++ b/test/lib/envutil.rb
@@ -150,6 +150,7 @@ def invoke_ruby(args, stdin_data = "", capture_stdout = false, capture_stderr =
         timeout_error = nil
       else
         status = terminate(pid, signal, opt[:pgroup], reprieve)
+        terminated = Time.now
       end
       stdout = th_stdout.value if capture_stdout
       stderr = th_stderr.value if capture_stderr && capture_stderr != :merge_to_stdout
@@ -161,7 +162,7 @@ def invoke_ruby(args, stdin_data = "", capture_stdout = false, capture_stderr =
       if timeout_error
         bt = caller_locations
         msg = "execution of #{bt.shift.label} expired timeout (#{timeout} sec)"
-        msg = Test::Unit::Assertions::FailDesc[status, msg, [stdout, stderr].join("\n")].()
+        msg = failure_description(status, terminated, msg, [stdout, stderr].join("\n"))
         raise timeout_error, msg, bt.map(&:to_s)
       end
       return stdout, stderr, status
@@ -286,6 +287,37 @@ def self.diagnostic_reports(signame, pid, now)
     end
   end
 
+  def self.failure_description(status, now, message = "", out = "")
+    pid = status.pid
+    if signo = status.termsig
+      signame = Signal.signame(signo)
+      sigdesc = "signal #{signo}"
+    end
+    log = diagnostic_reports(signame, pid, now)
+    if signame
+      sigdesc = "SIG#{signame} (#{sigdesc})"
+    end
+    if status.coredump?
+      sigdesc = "#{sigdesc} (core dumped)"
+    end
+    full_message = ''.dup
+    message = message.call if Proc === message
+    if message and !message.empty?
+      full_message << message << "\n"
+    end
+    full_message << "pid #{pid}"
+    full_message << " exit #{status.exitstatus}" if status.exited?
+    full_message << " killed by #{sigdesc}" if sigdesc
+    if out and !out.empty?
+      full_message << "\n" << out.b.gsub(/^/, '| ')
+      full_message.sub!(/(?<!\n)\z/, "\n")
+    end
+    if log
+      full_message << "Diagnostic reports:\n" << log.b.gsub(/^/, '| ')
+    end
+    full_message
+  end
+
   def self.gc_stress_to_class?
     unless defined?(@gc_stress_to_class)
       _, _, status = invoke_ruby(["-e""exit GC.respond_to?(:add_stress_to_class)"])
@@ -304,7 +336,6 @@ class << self
     end
     dir = File.dirname(ruby)
     CONFIG['bindir'] = dir
-    Gem::ConfigMap[:bindir] = dir if defined?(Gem::ConfigMap)
   end
 end