Exit with a failure if any test files failed to load

Merged: https://github.com/ruby/ruby/pull/7897

tool/lib/test/unit.rb

@@ -813,6 +813,7 @@ module Test
             warn ""
             @warnings.uniq! {|w| w[1].message}
             @warnings.each do |w|
+              @errors += 1
               warn "#{w[0]}: #{w[1].message} (#{w[1].class})"
             end
             warn ""
@@ -1282,8 +1283,13 @@ module Test
             puts "#{f}: #{$!}"
           end
         }
+        @load_failed = errors.size.nonzero?
         result
       end
+
+      def run(*)
+        super or @load_failed
+      end
     end
 
     module RepeatOption # :nodoc: all
@@ -1680,7 +1686,7 @@ module Test
           break unless report.empty?
         end
 
-        return failures + errors if self.test_count > 0 # or return nil...
+        return (failures + errors).nonzero? # or return nil...
       rescue Interrupt
         abort 'Interrupted'
       end

tool/test/testunit/test4test_load_failure.rb

@@ -0,0 +1 @@
+raise LoadError, "no-such-library"

tool/test/testunit/test_load_failure.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+require 'test/unit'
+
+class TestLoadFailure < Test::Unit::TestCase
+  def test_load_failure
+    assert_not_predicate(load_failure, :success?)
+  end
+
+  def test_load_failure_parallel
+    assert_not_predicate(load_failure("-j2"), :success?)
+  end
+
+  private
+
+  def load_failure(*args)
+    IO.popen([*@options[:ruby], "#{__dir__}/../runner.rb",
+              "#{__dir__}/test4test_load_failure.rb",
+              "--verbose", *args], err: [:child, :out]) {|f|
+      assert_include(f.read, "test4test_load_failure.rb")
+    }
+    $?
+  end
+end