1 files changed, 37 insertions, 1 deletions
diff --git a/spec/ruby/library/stringio/ungetbyte_spec.rb b/spec/ruby/library/stringio/ungetbyte_spec.rb
index 701463e621..87b27b837e 100644
--- a/spec/ruby/library/stringio/ungetbyte_spec.rb
+++ b/spec/ruby/library/stringio/ungetbyte_spec.rb
@@ -1,6 +1,42 @@
+# frozen_string_literal: false
 require_relative '../../spec_helper'
 require 'stringio'
 
 describe "StringIO#ungetbyte" do
-  it "needs to be reviewed for spec completeness"
+  it "ungets a single byte from a string starting with a single byte character" do
+    str = 'This is a simple string.'
+    io = StringIO.new("#{str}")
+    c = io.getc
+    c.should == 'T'
+    io.ungetbyte(83)
+    io.string.should == 'Shis is a simple string.'
+  end
+
+  it "ungets a single byte from a string in the middle of a multibyte character" do
+    str = "\u01a9"
+    io = StringIO.new(str)
+    b = io.getbyte
+    b.should == 0xc6 # First byte of UTF-8 encoding of \u01a9
+    io.ungetbyte(0xce) # First byte of UTF-8 encoding of \u03a9
+    io.string.should == "\u03a9"
+  end
+
+  it "constrains the value of a numeric argument to a single byte" do
+    str = 'This is a simple string.'
+    io = StringIO.new("#{str}")
+    c = io.getc
+    c.should == 'T'
+    io.ungetbyte(83 | 0xff00)
+    io.string.should == 'Shis is a simple string.'
+  end
+
+  it "ungets the bytes of a string if given a string as an argument" do
+    str = "\u01a9"
+    io = StringIO.new(str)
+    b = io.getbyte
+    b.should == 0xc6 # First byte of UTF-8 encoding of \u01a9
+    io.ungetbyte("\u01a9")
+    io.string.bytes.should == [198, 169, 169]
+  end
+
 end