diff --git a/anki.d b/anki.d
index 1efa3f5..d827e22 100755
Binary files a/anki.d and b/anki.d differ
diff --git a/main.go b/main.go
index 311faaf..c3e96ce 100644
--- a/main.go
+++ b/main.go
@@ -14,7 +14,15 @@ import (
 )
 
 type (
-	DB struct {
+	DB interface {
+		HistoryOf(string) map[string][]History
+		Next(string, string) time.Time
+		Question(string) Question
+		LastAnswer(string, string) Answer
+		Answer(string) Answer
+		PushAnswer(string, string, string, bool) error
+	}
+	db struct {
 		Knowledge Knowledge
 		Users     map[string]User
 		Cadence   []Duration
@@ -88,28 +96,28 @@ func readline() string {
 }
 
 func NewDB() (DB, error) {
-	var db DB
+	var db db
 	if b, err := os.ReadFile(os.Getenv("DB")); err != nil {
-		return DB{}, err
+		return nil, err
 	} else if err := yaml.Unmarshal(b, &db); err != nil {
-		return DB{}, err
+		return nil, err
 	}
 	return db, nil
 }
 
-func (db DB) HistoryOf(user string) map[string][]History {
+func (db db) HistoryOf(user string) map[string][]History {
 	return db.Users[user].History
 }
 
-func (db DB) Question(q string) Question {
+func (db db) Question(q string) Question {
 	return db.Knowledge.Questions[q]
 }
 
-func (db DB) Answer(a string) Answer {
+func (db db) Answer(a string) Answer {
 	return db.Knowledge.Answers[a]
 }
 
-func (db DB) LastAnswer(user, q string) Answer {
+func (db db) LastAnswer(user, q string) Answer {
 	for _, v := range db.Knowledge.Answers {
 		if v.Q == q && v.Author == user {
 			return v
@@ -118,7 +126,7 @@ func (db DB) LastAnswer(user, q string) Answer {
 	return Answer{}
 }
 
-func (db DB) PushAnswer(user, q, a string, pass bool) error {
+func (db db) PushAnswer(user, q, a string, pass bool) error {
 	uuid := uuid.New().String()
 	db.Knowledge.Answers[uuid] = Answer{
 		Q:      q,
@@ -133,7 +141,7 @@ func (db DB) PushAnswer(user, q, a string, pass bool) error {
 	return nil
 }
 
-func (db DB) Next(user, q string) time.Time {
+func (db db) Next(user, q string) time.Time {
 	history := db.Users[user].History[q]
 	progress := 0
 	for i := range history {
@@ -151,7 +159,7 @@ func (db DB) Next(user, q string) time.Time {
 	return db.LastTS(user, q).Add(time.Duration(db.Cadence[progress]))
 }
 
-func (db DB) LastTS(user, q string) time.Time {
+func (db db) LastTS(user, q string) time.Time {
 	max := int64(0)
 	for _, v := range db.Users[user].History[q] {
 		if v.TS > max {