1 files changed, 19 insertions, 3 deletions
diff --git a/spec/ruby/core/io/readpartial_spec.rb b/spec/ruby/core/io/readpartial_spec.rb
index 2b33a0d5b1..0852f20b2d 100644
--- a/spec/ruby/core/io/readpartial_spec.rb
+++ b/spec/ruby/core/io/readpartial_spec.rb
@@ -59,10 +59,10 @@ describe "IO#readpartial" do
   end
 
   it "discards the existing buffer content upon successful read" do
-    buffer = "existing"
+    buffer = +"existing content"
     @wr.write("hello world")
     @wr.close
-    @rd.readpartial(11, buffer)
+    @rd.readpartial(11, buffer).should.equal?(buffer)
     buffer.should == "hello world"
   end
 
@@ -74,7 +74,7 @@ describe "IO#readpartial" do
   end
 
   it "discards the existing buffer content upon error" do
-    buffer = 'hello'
+    buffer = +'hello'
     @wr.close
     -> { @rd.readpartial(1, buffer) }.should raise_error(EOFError)
     buffer.should be_empty
@@ -93,4 +93,20 @@ describe "IO#readpartial" do
     @rd.readpartial(0).should == ""
   end
 
+  ruby_bug "#18421", ""..."3.0.4" do
+    it "clears and returns the given buffer if the length argument is 0" do
+      buffer = +"existing content"
+      @rd.readpartial(0, buffer).should == buffer
+      buffer.should == ""
+    end
+  end
+
+  it "preserves the encoding of the given buffer" do
+    buffer = ''.encode(Encoding::ISO_8859_1)
+    @wr.write("abc")
+    @wr.close
+    @rd.readpartial(10, buffer)
+
+    buffer.encoding.should == Encoding::ISO_8859_1
+  end
 end