diff --git a/.travis.yml b/.travis.yml
index 788ee8e..92b448d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,8 @@ install:
 script:
   - make install-dev-deps
   - make check-style
-  - make test
+  - make test-coverage
+  - make codecov
 
 matrix:
   fast_finish: true
diff --git a/bpe.go b/bpe.go
new file mode 100644
index 0000000..aca81fd
--- /dev/null
+++ b/bpe.go
@@ -0,0 +1,178 @@
+package bpe
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+
+	"github.com/sirupsen/logrus"
+)
+
+// TokenID is a numerical identitier of the subword token
+type TokenID uint32
+
+// EncodedToken is a sequence of subword tokens ids
+type EncodedToken []TokenID
+
+type rule struct {
+	left   TokenID
+	right  TokenID
+	result TokenID
+}
+
+type specialTokens struct {
+	unk int32
+	pad int32
+	bos int32
+	eos int32
+}
+
+// Model is a Byte-Pair encoding model, which supports encoding and decoding text into sequences
+// of most frequent subword tokens
+type Model struct {
+	char2id       map[rune]TokenID
+	id2char       map[TokenID]rune
+	rules         []rule
+	recipe        map[TokenID]EncodedToken
+	revRecipe     map[string]TokenID
+	specialTokens specialTokens
+}
+
+func newModel(nRules int) *Model {
+	return &Model{
+		make(map[rune]TokenID),
+		make(map[TokenID]rune),
+		make([]rule, nRules),
+		make(map[TokenID]EncodedToken),
+		make(map[string]TokenID),
+		specialTokens{-1, -1, -1, -1},
+	}
+}
+
+// DecodeToken converts the sequence of chars' ids into the string -
+// sequence of the corresponding chars
+func DecodeToken(token EncodedToken, id2char map[TokenID]rune) (string, error) {
+	word := ""
+	for _, id := range token {
+		if char, ok := id2char[id]; ok {
+			word = word + string(char)
+		} else {
+			logrus.Errorf("Decode failure: %d token id has no corresponding char", id)
+			return "", errors.New("key not found in id2char")
+		}
+	}
+	return word, nil
+}
+
+func (s specialTokens) toBinary() []byte {
+	bytesArray := make([]byte, 16)
+	binary.BigEndian.PutUint32(bytesArray, uint32(s.unk))
+	binary.BigEndian.PutUint32(bytesArray[4:], uint32(s.pad))
+	binary.BigEndian.PutUint32(bytesArray[8:], uint32(s.bos))
+	binary.BigEndian.PutUint32(bytesArray[12:], uint32(s.eos))
+	return bytesArray
+}
+
+func binaryToSpecialTokens(bytesArray []byte) (specialTokens, error) {
+	var s specialTokens
+	if len(bytesArray) < 16 {
+		logrus.Error("Bytes array length is too small")
+		return s, errors.New("bytes array is too small")
+	}
+	s.unk = int32(binary.BigEndian.Uint32(bytesArray))
+	s.pad = int32(binary.BigEndian.Uint32(bytesArray[4:]))
+	s.bos = int32(binary.BigEndian.Uint32(bytesArray[8:]))
+	s.eos = int32(binary.BigEndian.Uint32(bytesArray[12:]))
+	return s, nil
+}
+
+func (r rule) toBinary() []byte {
+	bytesArray := make([]byte, 12)
+	binary.BigEndian.PutUint32(bytesArray, uint32(r.left))
+	binary.BigEndian.PutUint32(bytesArray[4:], uint32(r.right))
+	binary.BigEndian.PutUint32(bytesArray[8:], uint32(r.result))
+	return bytesArray
+}
+
+func binaryToRule(bytesArray []byte) (rule, error) {
+	var r rule
+	if len(bytesArray) < 12 {
+		logrus.Error("Bytes array length is too small")
+		return r, errors.New("bytes array is too small")
+	}
+	r.left = TokenID(binary.BigEndian.Uint32(bytesArray))
+	r.right = TokenID(binary.BigEndian.Uint32(bytesArray[4:]))
+	r.result = TokenID(binary.BigEndian.Uint32(bytesArray[8:]))
+	return r, nil
+}
+
+// ReadModel loads the BPE model from the binary dump
+func ReadModel(reader io.Reader) (*Model, error) {
+	buf := make([]byte, 4)
+	var nChars, nRules int
+	if _, err := io.ReadFull(reader, buf); err != nil {
+		logrus.Error("Broken input: ", err)
+		return &Model{}, err
+	}
+	nChars = int(binary.BigEndian.Uint32(buf))
+	if _, err := io.ReadFull(reader, buf); err != nil {
+		logrus.Error("Broken input: ", err)
+		return &Model{}, err
+	}
+	nRules = int(binary.BigEndian.Uint32(buf))
+
+	model := newModel(nRules)
+	for i := 0; i < nChars; i++ {
+		var char rune
+		var charID TokenID
+		if _, err := io.ReadFull(reader, buf); err != nil {
+			logrus.Error("Broken input: ", err)
+			return &Model{}, err
+		}
+		char = rune(binary.BigEndian.Uint32(buf))
+		if _, err := io.ReadFull(reader, buf); err != nil {
+			logrus.Error("Broken input: ", err)
+			return &Model{}, err
+		}
+		charID = TokenID(binary.BigEndian.Uint32(buf))
+		model.char2id[char] = charID
+		model.id2char[charID] = char
+		model.recipe[charID] = EncodedToken{charID}
+		model.revRecipe[string(char)] = charID
+	}
+	ruleBuf := make([]byte, 12)
+	for i := 0; i < nRules; i++ {
+		if _, err := io.ReadFull(reader, ruleBuf); err != nil {
+			logrus.Error("Broken input: ", err)
+			return &Model{}, err
+		}
+		rule, err := binaryToRule(ruleBuf)
+		if err != nil {
+			return model, err
+		}
+		model.rules[i] = rule
+		if _, ok := model.recipe[rule.left]; !ok {
+			logrus.Errorf("%d: token id not described before", rule.left)
+			return model, errors.New("key not found in id2char")
+		}
+		if _, ok := model.recipe[rule.right]; !ok {
+			logrus.Errorf("%d: token id not described before", rule.right)
+			return model, errors.New("key not found in id2char")
+		}
+		model.recipe[rule.result] = append(model.recipe[rule.left], model.recipe[rule.right]...)
+		resultString, err := DecodeToken(model.recipe[rule.result], model.id2char)
+		if err != nil {
+			logrus.Error("Unexpected token id inside the rules: ", err)
+			return model, err
+		}
+		model.revRecipe[resultString] = rule.result
+	}
+	specialTokensBuf := make([]byte, 16)
+	if _, err := io.ReadFull(reader, specialTokensBuf); err != nil {
+		logrus.Error("Broken input: ", err)
+		return &Model{}, err
+	}
+	specials, err := binaryToSpecialTokens(specialTokensBuf)
+	model.specialTokens = specials
+	return model, err
+}
diff --git a/bpe_test.go b/bpe_test.go
new file mode 100644
index 0000000..e69398b
--- /dev/null
+++ b/bpe_test.go
@@ -0,0 +1,131 @@
+package bpe
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewModel(t *testing.T) {
+	model := newModel(10)
+	require.Equal(t, 10, len(model.rules))
+}
+
+func TestDecodeToken(t *testing.T) {
+	id2char := map[TokenID]rune{1: []rune("a")[0], 2: []rune("b")[0], 3: []rune("c")[0]}
+	word, err := DecodeToken(EncodedToken{1, 2, 1, 3, 3}, id2char)
+	require.NoError(t, err)
+	require.Equal(t, "abacc", word)
+}
+
+func TestSpecialTokensToBinary(t *testing.T) {
+	specials := specialTokens{1, 259, 2*256*256 + 37*256 + 2, -256 * 256 * 256 * 127}
+	bytesArray := []byte{0, 0, 0, 1, 0, 0, 1, 3, 0, 2, 37, 2, 129, 0, 0, 0}
+	require.Equal(t, bytesArray, specials.toBinary())
+}
+
+func TestBinaryToSpecialTokens(t *testing.T) {
+	bytesArray := []byte{0, 0, 0, 1, 0, 0, 1, 3, 0, 2, 37, 2, 129, 0, 0, 0}
+	expected := specialTokens{1, 259, 2*256*256 + 37*256 + 2, -256 * 256 * 256 * 127}
+	specials, err := binaryToSpecialTokens(bytesArray)
+	require.NoError(t, err)
+	require.Equal(t, expected, specials)
+	bytesArray = []byte{0, 0, 0, 1, 0, 0, 1, 3, 0, 2, 37, 2, 129, 0, 0}
+	specials, err = binaryToSpecialTokens(bytesArray)
+	require.Error(t, err)
+	bytesArray = []byte{}
+	specials, err = binaryToSpecialTokens(bytesArray)
+	require.Error(t, err)
+}
+
+func TestRuleToBinary(t *testing.T) {
+	rule := rule{1, 2, 257}
+	bytesArray := []byte{0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 1, 1}
+	require.Equal(t, bytesArray, rule.toBinary())
+}
+
+func TestBinaryToRule(t *testing.T) {
+	expected := rule{1, 2, 257}
+	bytesArray := []byte{0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 1, 1}
+	rule, err := binaryToRule(bytesArray)
+	require.NoError(t, err)
+	require.Equal(t, expected, rule)
+	bytesArray = []byte{0, 0, 0, 0, 0, 0, 2, 0, 0, 1, 1}
+	rule, err = binaryToRule(bytesArray)
+	require.Error(t, err)
+	bytesArray = []byte{}
+	rule, err = binaryToRule(bytesArray)
+	require.Error(t, err)
+}
+
+func TestReadModel(t *testing.T) {
+	reader := bytes.NewReader([]byte{0, 0, 0, 5, 0, 0, 0, 4,
+		0, 0, 0, 99, 0, 0, 0, 6,
+		0, 0, 0, 98, 0, 0, 0, 7,
+		0, 0, 0, 95, 0, 0, 0, 4,
+		0, 0, 0, 100, 0, 0, 0, 5,
+		0, 0, 0, 97, 0, 0, 0, 8,
+		0, 0, 0, 4, 0, 0, 0, 8, 0, 0, 0, 9,
+		0, 0, 0, 4, 0, 0, 0, 6, 0, 0, 0, 10,
+		0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 11,
+		0, 0, 0, 4, 0, 0, 0, 7, 0, 0, 0, 12,
+		0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 3})
+	expected := Model{
+		map[rune]TokenID{97: 8, 98: 7, 99: 6, 100: 5, 95: 4},
+		map[TokenID]rune{4: 95, 5: 100, 6: 99, 7: 98, 8: 97},
+		[]rule{{4, 8, 9}, {4, 6, 10}, {4, 5, 11}, {4, 7, 12}},
+		map[TokenID]EncodedToken{4: {4}, 5: {5}, 6: {6}, 7: {7}, 8: {8}, 9: {4, 8}, 10: {4, 6}, 11: {4, 5}, 12: {4, 7}},
+		map[string]TokenID{"a": 8, "b": 7, "c": 6, "d": 5, "_": 4,
+			"_a": 9, "_b": 12, "_c": 10, "_d": 11},
+		specialTokens{1, 0, 2, 3},
+	}
+	model, err := ReadModel(reader)
+	require.NoError(t, err)
+	require.Equal(t, expected, *model)
+
+	reader = bytes.NewReader([]byte{0, 0, 0, 5, 0, 0, 0, 4,
+		0, 0, 0, 99, 0, 0, 0, 6,
+		0, 0, 0, 98, 0, 0, 0, 7,
+		0, 0, 0, 95, 0, 0, 0, 4,
+		0, 0, 0, 100, 0, 0, 0, 5,
+		0, 0, 0, 97, 0, 0, 0, 8,
+		0, 0, 0, 4, 0, 0, 0, 8, 0, 0, 0, 9,
+		0, 0, 0, 4, 0, 0, 0, 6, 0, 0, 0, 10,
+		0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 11,
+		0, 0, 0, 4, 0, 0, 0, 7, 0, 0, 0, 12,
+		0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 3,
+		0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 11,
+		0, 0, 0, 4, 0, 0, 0, 7, 0, 0, 0, 12})
+	model, err = ReadModel(reader)
+	require.NoError(t, err)
+	require.Equal(t, expected, *model)
+
+	reader = bytes.NewReader([]byte{0, 0, 0, 5, 0, 0, 0, 4,
+		0, 0, 0, 99, 0, 0, 0, 6,
+		0, 0, 0, 98, 0, 0, 0, 7,
+		0, 0, 0, 95, 0, 0, 0, 4,
+		0, 0, 0, 100, 0, 0, 0, 5,
+		0, 0, 0, 97, 0, 0, 0, 8,
+		0, 0, 0, 4, 0, 0, 0, 8, 0, 0, 0, 9,
+		0, 0, 0, 4, 0, 0, 0, 6, 0, 0, 0, 10,
+		0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 11,
+		0, 0, 0, 4, 0, 0, 0, 7, 0, 0, 0, 12,
+		0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0})
+	model, err = ReadModel(reader)
+	require.Error(t, err)
+
+	reader = bytes.NewReader([]byte{0, 0, 0, 5, 0, 0, 0, 4,
+		0, 0, 0, 99, 0, 0, 0, 6,
+		0, 0, 0, 98, 0, 0, 0, 7,
+		0, 0, 0, 95, 0, 0, 0, 4,
+		0, 0, 0, 100, 0, 0, 0, 5,
+		0, 0, 0, 97, 0, 0, 0, 8,
+		0, 0, 0, 4, 0, 0, 0, 20, 0, 0, 0, 9,
+		0, 0, 0, 4, 0, 0, 0, 6, 0, 0, 0, 10,
+		0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 11,
+		0, 0, 0, 4, 0, 0, 0, 7, 0, 0, 0, 12,
+		0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 3})
+	model, err = ReadModel(reader)
+	require.Error(t, err)
+}
diff --git a/go.mod b/go.mod
index 7d8e300..510e312 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,8 @@
 module github.com/src-d/go-YouTokenToMe
 
 go 1.12
+
+require (
+	github.com/sirupsen/logrus v1.4.2
+	github.com/stretchr/testify v1.4.0
+)
diff --git a/go.sum b/go.sum
deleted file mode 100644
index e69de29..0000000
diff --git a/main.go b/main.go
deleted file mode 100644
index 953cd3d..0000000
--- a/main.go
+++ /dev/null
@@ -1,7 +0,0 @@
-package main
-
-import "fmt"
-
-func main() {
-	fmt.Printf("Package for applying BPE")
-}