1 files changed, 39 insertions, 5 deletions
diff --git a/spec/ruby/core/io/sysread_spec.rb b/spec/ruby/core/io/sysread_spec.rb
index 024200efea..003bb9eb94 100644
--- a/spec/ruby/core/io/sysread_spec.rb
+++ b/spec/ruby/core/io/sysread_spec.rb
@@ -6,7 +6,7 @@ describe "IO#sysread on a file" do
     @file_name = tmp("IO_sysread_file") + $$.to_s
     File.open(@file_name, "w") do |f|
       # write some stuff
-      f.write("012345678901234567890123456789")
+      f.write("012345678901234567890123456789\nabcdef")
     end
     @file = File.open(@file_name, "r+")
   end
@@ -21,25 +21,25 @@ describe "IO#sysread on a file" do
   end
 
   it "reads the specified number of bytes from the file to the buffer" do
-    buf = "" # empty buffer
+    buf = +"" # empty buffer
     @file.sysread(15, buf).should == buf
     buf.should == "012345678901234"
 
     @file.rewind
 
-    buf = "ABCDE" # small buffer
+    buf = +"ABCDE" # small buffer
     @file.sysread(15, buf).should == buf
     buf.should == "012345678901234"
 
     @file.rewind
 
-    buf = "ABCDE" * 5 # large buffer
+    buf = +"ABCDE" * 5 # large buffer
     @file.sysread(15, buf).should == buf
     buf.should == "012345678901234"
   end
 
   it "coerces the second argument to string and uses it as a buffer" do
-    buf = "ABCDE"
+    buf = +"ABCDE"
     (obj = mock("buff")).should_receive(:to_str).any_number_of_times.and_return(buf)
     @file.sysread(15, obj).should == buf
     buf.should == "012345678901234"
@@ -50,6 +50,11 @@ describe "IO#sysread on a file" do
     @file.sysread(5).should == "56789"
   end
 
+  it "raises an error when called after buffered reads" do
+    @file.readline
+    -> { @file.sysread(5) }.should raise_error(IOError)
+  end
+
   it "reads normally even when called immediately after a buffered IO#read" do
     @file.read(15)
     @file.sysread(5).should == "56789"
@@ -79,6 +84,29 @@ describe "IO#sysread on a file" do
   it "raises IOError on closed stream" do
     -> { IOSpecs.closed_io.sysread(5) }.should raise_error(IOError)
   end
+
+  it "immediately returns an empty string if the length argument is 0" do
+    @file.sysread(0).should == ""
+  end
+
+  it "immediately returns the given buffer if the length argument is 0" do
+    buffer = +"existing content"
+    @file.sysread(0, buffer).should == buffer
+    buffer.should == "existing content"
+  end
+
+  it "discards the existing buffer content upon successful read" do
+    buffer = +"existing content"
+    @file.sysread(11, buffer)
+    buffer.should == "01234567890"
+  end
+
+  it "discards the existing buffer content upon error" do
+    buffer = +"existing content"
+    @file.seek(0, :END)
+    -> { @file.sysread(1, buffer) }.should raise_error(EOFError)
+    buffer.should be_empty
+  end
 end
 
 describe "IO#sysread" do
@@ -95,4 +123,10 @@ describe "IO#sysread" do
     @write.syswrite "ab"
     @read.sysread(3).should == "ab"
   end
+
+  guard_not -> { platform_is :windows and ruby_version_is ""..."3.2" } do # https://bugs.ruby-lang.org/issues/18880
+    it "raises ArgumentError when length is less than 0" do
+      -> { @read.sysread(-1) }.should raise_error(ArgumentError)
+    end
+  end
 end