show loadavg if the test fails

to survey the following failure:

```
  1) Failure:
TestFile#test_stat [/tmp/ruby/src/trunk-repeat20/test/ruby/test_file.rb:412]:
Expected |1770056232.744032 - 1770056230.6465776| (2.097454309463501) to be <= 1.
```

BTW I found that `test/ruby/test_file.rb:412` `assert_in_delta atime, stat.atime.to_f, delta`
only fails (mtime, ctime doesn't fail on 100 days).

tool/lib/test/unit/assertions.rb

@@ -128,8 +128,16 @@ module Test
 
       def assert_in_delta exp, act, delta = 0.001, msg = nil
         n = (exp - act).abs
+        loadavg = begin
+          if File.readable?("/proc/loadavg")
+            " (/proc/loadavg=#{File.read("/proc/loadavg").strip})"
+          end
+        rescue StandardError
+          nil
+        end
+        loadavg ||= ""
         msg = message(msg) {
-          "Expected |#{exp} - #{act}| (#{n}) to be <= #{delta}"
+          "Expected |#{exp} - #{act}| (#{n}) to be <= #{delta}#{loadavg}"
         }
         assert delta >= n, msg
       end

tool/test/testunit/test_minitest_unit.rb

@@ -646,7 +646,7 @@ class TestMiniTestUnitTestCase < Test::Unit::TestCase
 
   def test_assert_in_delta_triggered
     x = "1.0e-06"
-    util_assert_triggered "Expected |0.0 - 0.001| (0.001) to be <= #{x}." do
+    util_assert_triggered "Expected |0.0 - 0.001| (0.001) to be <= #{x}.", strip: /\s+\(\/proc\/loadavg=.*\)/ do
       @tc.assert_in_delta 0.0, 1.0 / 1000, 0.000001
     end
   end
@@ -678,7 +678,7 @@ class TestMiniTestUnitTestCase < Test::Unit::TestCase
   end
 
   def test_assert_in_epsilon_triggered
-    util_assert_triggered 'Expected |10000 - 9990| (10) to be <= 9.99.' do
+    util_assert_triggered 'Expected |10000 - 9990| (10) to be <= 9.99.', strip: /\s+\(\/proc\/loadavg=.*\)/ do
       @tc.assert_in_epsilon 10000, 9990
     end
   end
@@ -686,7 +686,7 @@ class TestMiniTestUnitTestCase < Test::Unit::TestCase
   def test_assert_in_epsilon_triggered_negative_case
     x = "0.100000xxx"
     y = "0.1"
-    util_assert_triggered "Expected |-1.1 - -1| (#{x}) to be <= #{y}." do
+    util_assert_triggered "Expected |-1.1 - -1| (#{x}) to be <= #{y}.", strip: /\s+\(\/proc\/loadavg=.*\)/ do
       @tc.assert_in_epsilon(-1.1, -1, 0.1)
     end
   end
@@ -1352,7 +1352,7 @@ class TestMiniTestUnitTestCase < Test::Unit::TestCase
     assert_equal expected, sample_test_case.test_methods.sort
   end
 
-  def assert_triggered expected, klass = Test::Unit::AssertionFailedError
+  def assert_triggered expected, klass = Test::Unit::AssertionFailedError, strip: nil
     e = assert_raise klass do
       yield
     end
@@ -1360,6 +1360,7 @@ class TestMiniTestUnitTestCase < Test::Unit::TestCase
     msg = e.message.sub(/(---Backtrace---).*/m, '\1')
     msg.gsub!(/\(oid=[-0-9]+\)/, '(oid=N)')
     msg.gsub!(/(\d\.\d{6})\d+/, '\1xxx') # normalize: ruby version, impl, platform
+    msg.gsub!(strip, '') if strip
 
     assert_equal expected, msg
   end