1 files changed, 49 insertions, 2 deletions
diff --git a/spec/ruby/core/time/utc_spec.rb b/spec/ruby/core/time/utc_spec.rb
index 74c17a93d1..566509fd33 100644
--- a/spec/ruby/core/time/utc_spec.rb
+++ b/spec/ruby/core/time/utc_spec.rb
@@ -4,8 +4,55 @@ require_relative 'shared/gmtime'
 require_relative 'shared/time_params'
 
 describe "Time#utc?" do
-  it "returns true if time represents a time in UTC (GMT)" do
-    Time.now.should_not.utc?
+  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.gmtime.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
+
+    ruby_version_is "3.1" do
+      Time.new(2022, 1, 1, 0, 0, 0, in: "UTC").utc?.should == true
+      Time.now(in: "UTC").utc?.should == true
+    end
+  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
+
+    ruby_version_is "3.1" do
+      Time.new(2022, 1, 1, 0, 0, 0, in: "Z").utc?.should == true
+      Time.now(in: "Z").utc?.should == true
+    end
+  end
+
+  ruby_version_is "3.1" do
+    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
+  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
+  end
+
+  it "does not treat time with 0 offset as UTC" do
+    Time.new(2022, 1, 1, 0, 0, 0, 0).utc?.should == false
   end
 end