Implement File#sysseek

lib/fakefs/file.rb

@@ -239,8 +239,9 @@ module FakeFS
       raise NotImplementedError
     end
 
-    def sysseek(offset, whence = SEEK_SET)
-      raise NotImplementedError
+    def sysseek(position, whence = SEEK_SET)
+      seek(position, whence)
+      pos
     end
 
     alias_method :to_i, :fileno

test/fake/file/sysseek_test.rb

@@ -0,0 +1,44 @@
+require "test_helper"
+
+class FileSysSeek < Test::Unit::TestCase
+  def setup
+    FakeFS.activate!
+    FakeFS::FileSystem.clear
+  end
+
+  def teardown
+    FakeFS.deactivate!
+  end
+
+  def test_should_seek_to_position
+    file = File.open("foo", "w") do |f|
+      f << "0123456789"
+    end
+
+    File.open("foo", "r") do |f|
+      f.sysseek(3)
+      assert_equal 3, f.pos
+
+      f.sysseek(0)
+      assert_equal 0, f.pos
+    end
+  end
+
+  def test_seek_returns_offset_into_file
+    File.open("foo", "w") do |f|
+      # 66 chars long
+      str = "0123456789" +
+            "0123456789" +
+            "0123456789" +
+            "0123456789" +
+            "0123456789" +
+            "0123456789" +
+            "012345"
+
+      f << str
+    end
+
+    f = File.open("foo")
+    assert_equal 53, f.sysseek(-13, IO::SEEK_END)
+  end
+end