diff --git a/internal/sequence/sequence.go b/internal/sequence/sequence.go
index 22fa86b..077de3f 100644
--- a/internal/sequence/sequence.go
+++ b/internal/sequence/sequence.go
@@ -33,7 +33,7 @@ type Sequence struct {
 }
 
 func (s *Sequence) String() string {
-	// 1<<64 -1 in base 32 is "3w5e11264sgsf" and uses 13 chars
+	// 1<<64 -1 in base 32 is "fvvvvvvvvvvvv" and uses 13 chars
 	return fmt.Sprintf("%013s-%013s", strconv.FormatUint(s.Epoch, 32), strconv.FormatUint(s.C, 32))
 }
 
@@ -45,6 +45,10 @@ func (s *Sequence) Reverse() *Sequence {
 }
 
 func Parse(s string) (*Sequence, error) {
+	if len(s) != 13*2+1 {
+		return nil, errors.Errorf("bad sequence %q string length", s)
+	}
+
 	parts := strings.Split(s, "-")
 	if len(parts) != 2 {
 		return nil, errors.Errorf("bad sequence %q", s)
diff --git a/internal/sequence/sequence_test.go b/internal/sequence/sequence_test.go
new file mode 100644
index 0000000..97623e2
--- /dev/null
+++ b/internal/sequence/sequence_test.go
@@ -0,0 +1,169 @@
+// Copyright 2019 Sorint.lab
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sequence
+
+import (
+	"errors"
+	"math"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestString(t *testing.T) {
+	tests := []struct {
+		name string
+		in   *Sequence
+		out  string
+	}{
+		{
+			name: "test zero value",
+			in: &Sequence{
+				Epoch: 0,
+				C:     0,
+			},
+			out: "0000000000000-0000000000000",
+		},
+		{
+			name: "test one value",
+			in: &Sequence{
+				Epoch: 1,
+				C:     1,
+			},
+			out: "0000000000001-0000000000001",
+		},
+		{
+			name: "test 32 value",
+			in: &Sequence{
+				Epoch: 32,
+				C:     32,
+			},
+			out: "0000000000010-0000000000010",
+		},
+		{
+			name: "test max uint 32 value",
+			in: &Sequence{
+				Epoch: math.MaxUint32,
+				C:     math.MaxUint32,
+			},
+			out: "0000003vvvvvv-0000003vvvvvv",
+		},
+		{
+			name: "test max value",
+			in: &Sequence{
+				Epoch: math.MaxUint64,
+				C:     math.MaxUint64,
+			},
+			out: "fvvvvvvvvvvvv-fvvvvvvvvvvvv",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			out := tt.in.String()
+			if out != tt.out {
+				t.Fatalf("expected %q, got %q", tt.out, out)
+			}
+		})
+	}
+}
+
+func TestParse(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		out  *Sequence
+		err  error
+	}{
+		{
+			name: "test zero value",
+			in:   "0000000000000-0000000000000",
+			out: &Sequence{
+				Epoch: 0,
+				C:     0,
+			},
+		},
+		{
+			name: "test one value",
+			in:   "0000000000001-0000000000001",
+			out: &Sequence{
+				Epoch: 1,
+				C:     1,
+			},
+		},
+		{
+			name: "test 32 value",
+			in:   "0000000000010-0000000000010",
+			out: &Sequence{
+				Epoch: 32,
+				C:     32,
+			},
+		},
+		{
+			name: "test max uint 32 value",
+			in:   "0000003vvvvvv-0000003vvvvvv",
+			out: &Sequence{
+				Epoch: math.MaxUint32,
+				C:     math.MaxUint32,
+			},
+		},
+		{
+			name: "test max value",
+			in:   "fvvvvvvvvvvvv-fvvvvvvvvvvvv",
+			out: &Sequence{
+				Epoch: math.MaxUint64,
+				C:     math.MaxUint64,
+			},
+		},
+		{
+			name: "test wrong string length",
+			in:   "fvvvvvvvvvvvv-fvvvvvvvvvvv",
+			out: &Sequence{
+				Epoch: math.MaxUint64,
+				C:     math.MaxUint64,
+			},
+			err: errors.New(`bad sequence "fvvvvvvvvvvvv-fvvvvvvvvvvv" string length`),
+		},
+		{
+			name: "test wrong string format",
+			in:   "fvvvvvvvvvvvv-fvvv-vvvvvvvv",
+			out: &Sequence{
+				Epoch: math.MaxUint64,
+				C:     math.MaxUint64,
+			},
+			err: errors.New(`bad sequence "fvvvvvvvvvvvv-fvvv-vvvvvvvv"`),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			out, err := Parse(tt.in)
+			if err != nil {
+				if tt.err == nil {
+					t.Fatalf("got error: %v, want nil error", err)
+				}
+				if tt.err.Error() != err.Error() {
+					t.Fatalf("got error: %v, want error: %v", err, tt.err)
+				}
+				return
+			} else if tt.err != nil {
+				t.Fatalf("got nil error, want error: %v", tt.err)
+			}
+			if diff := cmp.Diff(tt.out, out); diff != "" {
+				t.Fatal(diff)
+			}
+		})
+	}
+}