Add File#syswrite, File#sysread. Closes Github fakefs#26

lib/fakefs/file.rb

@@ -216,7 +216,9 @@ def exists?
       true
     end
 
-    alias_method :tell=, :pos=
+    alias_method :tell=,    :pos=
+    alias_method :sysread,  :read
+    alias_method :syswrite, :write
 
     undef_method :closed_read?
     undef_method :closed_write?

test/fake/file/syswrite_test.rb

@@ -0,0 +1,62 @@
+require "test_helper"
+
+class FileSysWriteTest < Test::Unit::TestCase
+  def setup
+    FakeFS.activate!
+    FakeFS::FileSystem.clear
+  end
+
+  def teardown
+    FakeFS.deactivate!
+  end
+
+  def test_returns_one_byte_when_written
+    f = File.open "foo", "w"
+    result = f.syswrite "a"
+    assert_equal 1, result
+  end
+
+  def test_returns_two_bytes_when_two_written
+    f = File.open "foo", "w"
+    result = f.syswrite "ab"
+    assert_equal 2, result
+  end
+
+  def test_syswrite_writes_file
+    f = File.open "foo", "w"
+    f.syswrite "abcdef"
+    f.close
+
+    assert_equal "abcdef", File.read("foo")
+  end
+
+  def test_writes_to_the_actual_position_when_called_after_buffered_io_read
+    File.open("foo", "w") do |file|
+      file.syswrite("012345678901234567890123456789")
+    end
+
+    file = File.open("foo", "r+")
+    file.read(5)
+    file.syswrite("abcde")
+
+    File.open("foo") do |file|
+      assert_equal "01234abcde", file.sysread(10)
+    end
+  end
+
+  def test_writes_all_of_the_strings_bytes_but_does_not_buffer_them
+    File.open("foo", "w") do |file|
+      file.syswrite("012345678901234567890123456789")
+    end
+
+    file = File.open("foo", "r+")
+    written = file.syswrite("abcde")
+
+    File.open("foo") do |file|
+      assert_equal "abcde56789", file.sysread(10)
+      file.seek(0)
+      file.fsync
+      assert_equal "abcde56789", file.sysread(10)
+    end
+  end
+end