Add specs for IO.pread

core/io/pread_spec.rb

@@ -0,0 +1,52 @@
+# -*- encoding: utf-8 -*-
+require_relative '../../spec_helper'
+
+ruby_version_is "2.5" do
+  platform_is_not :windows do
+    describe "IO#pread" do
+      before :each do
+        @fname = tmp("io_pread.txt")
+        @contents = "1234567890"
+        touch(@fname) { |f| f.write @contents }
+        @file = File.open(@fname, "r+")
+      end
+
+      after :each do
+        @file.close
+        rm_r @fname
+      end
+
+      it "accepts a length, and an offset" do
+        @file.pread(4, 0).should == "1234"
+        @file.pread(3, 4).should == "567"
+      end
+
+      it "accepts a length, an offset, and an output buffer" do
+        buffer = "foo"
+        @file.pread(3, 4, buffer)
+        buffer.should == "567"
+      end
+
+      it "does not advance the file pointer" do
+        @file.pread(4, 0).should == "1234"
+        @file.read.should == "1234567890"
+      end
+
+      it "raises EOFError if end-of-file is reached" do
+        lambda { @file.pread(1, 10) }.should raise_error(EOFError)
+      end
+
+      it "raises IOError when file is not open in read mode" do
+        File.open(@fname, "w") do |file|
+          lambda { file.pread(1, 1) }.should raise_error(IOError)
+        end
+      end
+
+      it "raises IOError when file is closed" do
+        file = File.open(@fname, "r+")
+        file.close
+        lambda { file.pread(1, 1) }.should raise_error(IOError)
+      end
+    end
+  end
+end