adds more specific specs for cesu-8 encoding

core/encoding/list_spec.rb

@@ -36,6 +36,16 @@
     Encoding.list.select {|e| e.dummy?}.should_not == []
   end
 
+  it 'includes UTF-8 encoding' do
+    Encoding.list.include?(Encoding::UTF_8).should be_true
+  end
+
+  ruby_version_is "2.7" do
+    it 'includes CESU-8 encoding' do
+      Encoding.list.include?(Encoding::CESU_8).should be_true
+    end
+  end
+
   # TODO: Find example that illustrates this
   it "updates the list when #find is used to load a new encoding"
 end

core/integer/chr_spec.rb

@@ -240,4 +240,17 @@
       -> { integer.chr(encoding_name) }.should raise_error(RangeError)
     end
   end
+
+  ruby_version_is "2.7" do
+    it 'returns a String encoding self interpreted as a codepoint in the CESU-8 encoding' do
+      # see more details here https://en.wikipedia.org/wiki/CESU-8
+      # code points from U+0000 to U+FFFF is encoded in the same way as in UTF-8
+      0x0045.chr(Encoding::CESU_8).bytes.should == 0x0045.chr(Encoding::UTF_8).bytes
+
+      # code points in range from U+10000 to U+10FFFF is CESU-8 data containing a 6-byte surrogate pair,
+      # which decodes to a 4-byte UTF-8 string
+      0x10400.chr(Encoding::CESU_8).bytes.should != 0x10400.chr(Encoding::UTF_8).bytes
+      0x10400.chr(Encoding::CESU_8).bytes.to_a.should == [0xED, 0xA0, 0x81, 0xED, 0xB0, 0x80]
+    end
+  end
 end

core/string/valid_encoding_spec.rb

@@ -98,9 +98,6 @@
     str.force_encoding('MacJapanese').valid_encoding?.should be_false
     str.force_encoding('UTF-7').valid_encoding?.should be_true
     str.force_encoding('UTF8-MAC').valid_encoding?.should be_true
-    ruby_version_is "2.7" do
-      str.force_encoding('CESU-8').valid_encoding?.should be_true
-    end
   end
 
   it "returns false if self is valid in one encoding, but invalid in the one it's tagged with" do