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diff --git a/spec/ruby/core/time/utc_spec.rb b/spec/ruby/core/time/utc_spec.rb
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+++ b/spec/ruby/core/time/utc_spec.rb
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+require_relative '../../spec_helper'
+require_relative 'shared/time_params'
+
+describe "Time#utc?" do
+  it "returns true only if time represents a time in UTC (GMT)" do
+    Time.now.utc?.should == false
+    Time.now.utc.utc?.should == true
+  end
+
+  it "treats time as UTC what was created in different ways" do
+    Time.now.utc.utc?.should == true
+    Time.now.utc.utc?.should == true
+    Time.now.getgm.utc?.should == true
+    Time.now.getutc.utc?.should == true
+    Time.utc(2022).utc?.should == true
+  end
+
+  it "does treat time with 'UTC' offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, "UTC").utc?.should == true
+    Time.now.localtime("UTC").utc?.should == true
+    Time.at(Time.now, in: 'UTC').utc?.should == true
+
+    Time.new(2022, 1, 1, 0, 0, 0, in: "UTC").utc?.should == true
+    Time.now(in: "UTC").utc?.should == true
+  end
+
+  it "does treat time with Z offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, "Z").utc?.should == true
+    Time.now.localtime("Z").utc?.should == true
+    Time.at(Time.now, in: 'Z').utc?.should == true
+
+    Time.new(2022, 1, 1, 0, 0, 0, in: "Z").utc?.should == true
+    Time.now(in: "Z").utc?.should == true
+  end
+
+  it "does treat time with -00:00 offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, "-00:00").utc?.should == true
+    Time.now.localtime("-00:00").utc?.should == true
+    Time.at(Time.now, in: '-00:00').utc?.should == true
+  end
+
+  it "does not treat time with +00:00 offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, "+00:00").utc?.should == false
+    Time.now.localtime("+00:00").utc?.should == false
+    Time.at(Time.now, in: "+00:00").utc?.should == false
+  end
+
+  it "does not treat time with 0 offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, 0).utc?.should == false
+    Time.now.localtime(0).utc?.should == false
+    Time.at(Time.now, in: 0).utc?.should == false
+  end
+end
+
+describe "Time.utc" do
+  it_behaves_like :time_params, :utc
+  it_behaves_like :time_params_10_arg, :utc
+  it_behaves_like :time_params_microseconds, :utc
+
+  it "creates a time based on given values, interpreted as UTC (GMT)" do
+    Time.utc(2000,"jan",1,20,15,1).inspect.should == "2000-01-01 20:15:01 UTC"
+  end
+
+  it "creates a time based on given C-style gmtime arguments, interpreted as UTC (GMT)" do
+    time = Time.utc(1, 15, 20, 1, 1, 2000, :ignored, :ignored, :ignored, :ignored)
+    time.inspect.should == "2000-01-01 20:15:01 UTC"
+  end
+
+  it "interprets pre-Gregorian reform dates using Gregorian proleptic calendar" do
+    Time.utc(1582, 10, 4, 12).to_i.should == -12220200000 # 2299150j
+  end
+
+  it "interprets Julian-Gregorian gap dates using Gregorian proleptic calendar" do
+    Time.utc(1582, 10, 14, 12).to_i.should == -12219336000 # 2299160j
+  end
+
+  it "interprets post-Gregorian reform dates using Gregorian calendar" do
+    Time.utc(1582, 10, 15, 12).to_i.should == -12219249600 # 2299161j
+  end
+
+  it "handles fractional usec close to rounding limit" do
+    time = Time.utc(2000, 1, 1, 12, 30, 0, 9999r/10000)
+
+    time.usec.should == 0
+    time.nsec.should == 999
+  end
+
+  guard -> {
+    with_timezone 'right/UTC' do
+      (Time.utc(1972, 6, 30, 23, 59, 59) + 1).sec == 60
+    end
+  } do
+    it "handles real leap seconds in zone 'right/UTC'" do
+      with_timezone 'right/UTC' do
+        time = Time.utc(1972, 6, 30, 23, 59, 60)
+
+        time.sec.should == 60
+        time.min.should == 59
+        time.hour.should == 23
+        time.day.should == 30
+        time.month.should == 6
+      end
+    end
+  end
+
+  it "handles bad leap seconds by carrying values forward" do
+    with_timezone 'UTC' do
+      time = Time.utc(2017, 7, 5, 23, 59, 60)
+      time.sec.should == 0
+      time.min.should == 0
+      time.hour.should == 0
+      time.day.should == 6
+      time.month.should == 7
+    end
+  end
+
+  it "handles a value of 60 for seconds by carrying values forward in zone 'UTC'" do
+    with_timezone 'UTC' do
+      time = Time.utc(1972, 6, 30, 23, 59, 60)
+
+      time.sec.should == 0
+      time.min.should == 0
+      time.hour.should == 0
+      time.day.should == 1
+      time.month.should == 7
+    end
+  end
+end
+
+describe "Time#utc" do
+  it "converts self to UTC, modifying the receiver" do
+    # Testing with America/Regina here because it doesn't have DST.
+    with_timezone("CST", -6) do
+      t = Time.local(2007, 1, 9, 6, 0, 0)
+      t.utc
+      # Time#== compensates for time zones, so check all parts separately
+      t.year.should == 2007
+      t.month.should == 1
+      t.mday.should == 9
+      t.hour.should == 12
+      t.min.should == 0
+      t.sec.should == 0
+      t.zone.should == "UTC"
+    end
+  end
+
+  it "returns self" do
+    with_timezone("CST", -6) do
+      t = Time.local(2007, 1, 9, 12, 0, 0)
+      t.utc.should.equal?(t)
+    end
+  end
+
+  describe "on a frozen time" do
+    it "does not raise an error if already in UTC" do
+      time = Time.gm(2007, 1, 9, 12, 0, 0)
+      time.freeze
+      time.utc.should.equal?(time)
+    end
+
+    it "raises a FrozenError if the time is not UTC" do
+      with_timezone("CST", -6) do
+        time = Time.now
+        time.freeze
+        -> { time.utc }.should.raise(FrozenError)
+      end
+    end
+  end
+end