Debug random failure of ruby-spec on ci.rvm.jp

spec/ruby/core/process/times_spec.rb

@@ -16,14 +16,42 @@ describe "Process.times" do
   ruby_version_is "2.5" do
     platform_is_not :windows do
       it "uses getrusage when available to improve precision beyond milliseconds" do
-        times = 100.times.map { Process.clock_gettime(:GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID) }
+        gettimes = 100.times.map { Process.clock_gettime(:GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID) }
-        if times.count { |t| ((t * 1e6).to_i % 1000) > 0 } == 0
+        if gettimes.count { |t| ((t * 1e6).to_i % 1000) > 0 } == 0
           skip "getrusage is not supported on this environment"
         end
 
         times = 100.times.map { Process.times }
-        times.count { |t| ((t.utime * 1e6).to_i % 1000) > 0 }.should > 0
+
-        times.count { |t| ((t.stime * 1e6).to_i % 1000) > 0 }.should > 0
+        # Creating custom matcher to show a debug message to investigate random failure
+        # on Debian ci.rvm.jp like: https://gist.github.com/ko1/346983a66ba66cf288249383ca30f15a
+        larger_than_0 = Class.new do
+          def initialize(expected, times:, gettimes:)
+            @expected = expected
+            @times = times
+            @gettimes = gettimes
+          end
+
+          def matches?(actual)
+            @actual = actual
+            @actual > @expected
+          end
+
+          def failure_message
+            ["Expected #{@actual} > #{@expected}",
+             "to be truthy but was false. (times: #{pp(@times)}, gettimes: #{pp(@gettimes)})"]
+          end
+
+          alias :negative_failure_message :failure_message
+
+          private def pp(obj)
+            require 'pp'
+            PP.pp(obj, '')
+          end
+        end.new(0, times: times, gettimes: gettimes)
+
+        times.count { |t| ((t.utime * 1e6).to_i % 1000) > 0 }.should(larger_than_0)
+        times.count { |t| ((t.stime * 1e6).to_i % 1000) > 0 }.should(larger_than_0)
       end
     end
   end