storage/filesystem: compare files using offset in test

Using equals to compare files it uses diff to do so. This can
potentially consume lots of ram. Changed the comparison to use file
offsets. If the descriptor is reused the offset is maintained.

Signed-off-by: Javi Fontan <jfontan@gmail.com>

Author: jfontan

storage/filesystem/dotgit/dotgit_test.go

@@ -474,16 +474,27 @@ func (s *SuiteDotGit) TestObjectPackWithKeepDescriptors(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(filepath.Ext(pack.Name()), Equals, ".pack")
 
+	// Move to an specific offset
+	pack.Seek(42, os.SEEK_SET)
+
 	pack2, err := dir.ObjectPack(f.PackfileHash)
 	c.Assert(err, IsNil)
-	c.Assert(pack, Equals, pack2)
+
+	// If the file is the same the offset should be the same
+	offset, err := pack2.Seek(0, os.SEEK_CUR)
+	c.Assert(err, IsNil)
+	c.Assert(offset, Equals, int64(42))
 
 	err = dir.Close()
 	c.Assert(err, IsNil)
 
 	pack2, err = dir.ObjectPack(f.PackfileHash)
 	c.Assert(err, IsNil)
-	c.Assert(pack, Not(Equals), pack2)
+
+	// If the file is opened again its offset should be 0
+	offset, err = pack2.Seek(0, os.SEEK_CUR)
+	c.Assert(err, IsNil)
+	c.Assert(offset, Equals, int64(0))
 
 	err = pack2.Close()
 	c.Assert(err, IsNil)

storage/filesystem/object_test.go

@@ -2,6 +2,7 @@ package filesystem
 
 import (
 	"io/ioutil"
+	"os"
 	"testing"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -66,12 +67,17 @@ func (s *FsSuite) TestGetFromPackfileKeepDescriptors(c *C) {
 		pack1, err := dg.ObjectPack(packfiles[0])
 		c.Assert(err, IsNil)
 
+		pack1.Seek(42, os.SEEK_SET)
+
 		err = o.Close()
 		c.Assert(err, IsNil)
 
 		pack2, err := dg.ObjectPack(packfiles[0])
 		c.Assert(err, IsNil)
-		c.Assert(pack1, Not(Equals), pack2)
+
+		offset, err := pack2.Seek(0, os.SEEK_CUR)
+		c.Assert(err, IsNil)
+		c.Assert(offset, Equals, int64(0))
 
 		err = o.Close()
 		c.Assert(err, IsNil)