1 files changed, 55 insertions, 0 deletions
diff --git a/spec/ruby/core/process/clock_getres_spec.rb b/spec/ruby/core/process/clock_getres_spec.rb
new file mode 100644
index 0000000000..35180bc81b
--- /dev/null
+++ b/spec/ruby/core/process/clock_getres_spec.rb
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+require_relative '../../spec_helper'
+require_relative 'fixtures/clocks'
+
+describe "Process.clock_getres" do
+  ProcessSpecs.clock_constants.each do |name, value|
+    it "matches the clock in practice for Process::#{name}" do
+      times = []
+      10_000.times do
+        times << Process.clock_gettime(value, :nanosecond)
+      end
+      reported = Process.clock_getres(value, :nanosecond)
+
+      # The clock should not be more accurate than reported (times should be
+      # a multiple of reported precision.)
+      times.select { |t| t % reported > 0 }.should be_empty
+
+      # We're assuming precision is a multiple of ten - it may or may not
+      # be an incompatibility if it isn't but we'd like to notice this,
+      # and the spec following these wouldn't work if it isn't.
+      reported.should > 0
+      (reported == 1 || reported % 10 == 0).should be_true
+
+      # The clock should not be less accurate than reported (times should
+      # not all be a multiple of the next precision up, assuming precisions
+      # are multiples of ten.)
+      times.select { |t| t % (reported * 10) == 0  }.size.should_not == times.size
+    end
+  end
+
+  # These are documented
+
+  it "with :GETTIMEOFDAY_BASED_CLOCK_REALTIME reports 1 microsecond" do
+    Process.clock_getres(:GETTIMEOFDAY_BASED_CLOCK_REALTIME, :nanosecond).should == 1_000
+  end
+
+  it "with :TIME_BASED_CLOCK_REALTIME reports 1 second" do
+    Process.clock_getres(:TIME_BASED_CLOCK_REALTIME, :nanosecond).should == 1_000_000_000
+  end
+
+  platform_is_not :windows do
+    it "with :GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID reports 1 microsecond" do
+      Process.clock_getres(:GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID, :nanosecond).should == 1_000
+    end
+  end
+
+  # These are observed
+
+  it "with Process::CLOCK_REALTIME reports at least 1 microsecond" do
+    Process.clock_getres(Process::CLOCK_REALTIME, :nanosecond).should <= 1_000
+  end
+
+  it "with Process::CLOCK_MONOTONIC reports at least 1 microsecond" do
+    Process.clock_getres(Process::CLOCK_MONOTONIC, :nanosecond).should <= 1_000
+  end
+end