Add test for ref.FromHash

ref/ref.go

@@ -40,8 +40,8 @@ func NewHash() hash.Hash {
 	return sha1.New()
 }
 
-// TODO: Test.
 func FromHash(h hash.Hash) Ref {
+	Chk.Equal(sha1.Size, h.Size())
 	digest := Sha1Digest{}
 	h.Sum(digest[:0])
 	return New(digest)

ref/ref_test.go

@@ -3,6 +3,7 @@ package ref
 import (
 	"testing"
 
+	"go/src/pkg/crypto/sha1"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -60,3 +61,10 @@ func TestDigest(t *testing.T) {
 	d[0] = 0x01
 	assert.NotEqual(t, r.Digest(), d)
 }
+
+func TestFromHash(t *testing.T) {
+	h := sha1.New()
+	h.Write([]byte("abc"))
+	r := FromHash(h)
+	assert.Equal(t, "sha1-a9993e364706816aba3e25717850c26c9cd0d89d", r.String())
+}