diff --git a/common/image.go b/common/image.go
index 86e57a6..e9e2c7a 100644
--- a/common/image.go
+++ b/common/image.go
@@ -16,22 +16,22 @@ import (
 	"time"
 )
 
-var rand uint32
-var randmu sync.Mutex
+var rrand uint32
+var rrandmu sync.Mutex
 
 func reseed() uint32 {
 	return uint32(time.Now().UnixNano() + int64(os.Getpid()))
 }
 
 func nextSuffix() string {
-	randmu.Lock()
-	r := rand
+	rrandmu.Lock()
+	r := rrand
 	if r == 0 {
 		r = reseed()
 	}
 	r = r*1664525 + 1013904223 // constants from Numerical Recipes
-	rand = r
-	randmu.Unlock()
+	rrand = r
+	rrandmu.Unlock()
 	return strconv.Itoa(int(1e9 + r%1e9))[1:]
 }
 
@@ -60,7 +60,7 @@ func tmpName(tmpl string) (string, error) {
 		}
 		if nconflict++; nconflict > 10 {
 			nconflict = 0
-			rand = reseed()
+			rrand = reseed()
 		}
 	}
 	return "", errors.New("Cannot create temp name")
diff --git a/common/spans.go b/common/spans.go
index b192de2..265d2ab 100644
--- a/common/spans.go
+++ b/common/spans.go
@@ -4,6 +4,11 @@
 
 package common
 
+import (
+	"bytes"
+	"fmt"
+)
+
 const chunkSize = 1024
 
 type Span struct {
@@ -184,3 +189,31 @@ func (sp *SpanPool) Insert(s *Span, pos, value int32) *Span {
 
 	return head
 }
+
+func (s *Span) Visit(v func(*Span)) {
+	for ; s != nil; s = s.Next {
+		v(s)
+	}
+}
+
+func (s *Span) Len() int {
+	n := 0
+	for ; s != nil; s = s.Next {
+		n++
+	}
+	return n
+}
+
+func (s *Span) String() string {
+	var buf bytes.Buffer
+	first := true
+	s.Visit(func(s1 *Span) {
+		if !first {
+			buf.WriteString(", ")
+		} else {
+			first = false
+		}
+		buf.WriteString(fmt.Sprintf("(%d, %d)", s1.From, s1.To))
+	})
+	return buf.String()
+}
diff --git a/common/spans_test.go b/common/spans_test.go
new file mode 100644
index 0000000..0144ccf
--- /dev/null
+++ b/common/spans_test.go
@@ -0,0 +1,36 @@
+// Copyright 2014 by Sascha L. Teichmann
+// Use of this source code is governed by the MIT license
+// that can be found in the LICENSE file.
+
+package common
+
+import (
+	"math/rand"
+	"testing"
+)
+
+func TestSpans(t *testing.T) {
+
+	inp := make([]int32, 3000)
+	for i, n := 0, len(inp); i < n; i++ {
+		inp[i] = int32(i)
+	}
+	for i, n := 0, len(inp); i < n; i++ {
+		i1 := rand.Int31n(int32(n))
+		i2 := rand.Int31n(int32(n))
+		inp[i1], inp[i2] = inp[i2], inp[i1]
+	}
+
+	sp := NewSpanPool()
+	var s *Span
+	for i, n := 0, len(inp); i < n; i++ {
+		s = sp.Insert(s, inp[i], 42)
+	}
+
+	if n := s.Len(); n != 1 {
+		t.Errorf("Span length %d expected 1\n", n)
+		t.Errorf("spans: %s\n", s)
+	}
+
+	sp.FreeAll(s)
+}