diff --git a/boomer.go b/boomer.go
index fb8b5d71..9bd62475 100644
--- a/boomer.go
+++ b/boomer.go
@@ -107,7 +107,7 @@ func (b *hrpBoomer) convertBoomerTask(testcase *TestCase) *boomer.Task {
 			for name, transaction := range runner.transactions {
 				if len(transaction) == 1 {
 					// if transaction end time not exists, use testcase end time instead
-					duration := endTime.Sub(transaction[TransactionStart])
+					duration := endTime.Sub(transaction[transactionStart])
 					b.RecordTransaction(name, transactionSuccess, duration.Milliseconds(), 0)
 				}
 			}
diff --git a/models.go b/models.go
index cbaf4b4e..34924faf 100644
--- a/models.go
+++ b/models.go
@@ -69,16 +69,16 @@ const (
 	stepTypeRendezvous  stepType = "rendezvous"
 )
 
-type TransactionType string
+type transactionType string
 
 const (
-	TransactionStart TransactionType = "start"
-	TransactionEnd   TransactionType = "end"
+	transactionStart transactionType = "start"
+	transactionEnd   transactionType = "end"
 )
 
 type Transaction struct {
 	Name string          `json:"name" yaml:"name"`
-	Type TransactionType `json:"type" yaml:"type"`
+	Type transactionType `json:"type" yaml:"type"`
 }
 type Rendezvous struct {
 	Name    string  `json:"name" yaml:"name"`                           // required
diff --git a/runner.go b/runner.go
index 68782c91..04058590 100644
--- a/runner.go
+++ b/runner.go
@@ -43,7 +43,7 @@ func NewRunner(t *testing.T) *hrpRunner {
 			Timeout: 30 * time.Second,
 		},
 		sessionVariables: make(map[string]interface{}),
-		transactions:     make(map[string]map[TransactionType]time.Time),
+		transactions:     make(map[string]map[transactionType]time.Time),
 	}
 }
 
@@ -55,7 +55,7 @@ type hrpRunner struct {
 	sessionVariables map[string]interface{}
 	// transactions stores transaction timing info.
 	// key is transaction name, value is map of transaction type and time, e.g. start time and end time.
-	transactions map[string]map[TransactionType]time.Time
+	transactions map[string]map[transactionType]time.Time
 	startTime    time.Time // record start time of the testcase
 }
 
@@ -63,7 +63,7 @@ type hrpRunner struct {
 func (r *hrpRunner) Reset() *hrpRunner {
 	log.Info().Msg("[init] Reset session variables")
 	r.sessionVariables = make(map[string]interface{})
-	r.transactions = make(map[string]map[TransactionType]time.Time)
+	r.transactions = make(map[string]map[transactionType]time.Time)
 	r.startTime = time.Now()
 	return r
 }
@@ -234,25 +234,25 @@ func (r *hrpRunner) runStepTransaction(transaction *Transaction) (stepResult *st
 
 	// create transaction if not exists
 	if _, ok := r.transactions[transaction.Name]; !ok {
-		r.transactions[transaction.Name] = make(map[TransactionType]time.Time)
+		r.transactions[transaction.Name] = make(map[transactionType]time.Time)
 	}
 
 	// record transaction start time, override if already exists
-	if transaction.Type == TransactionStart {
-		r.transactions[transaction.Name][TransactionStart] = time.Now()
+	if transaction.Type == transactionStart {
+		r.transactions[transaction.Name][transactionStart] = time.Now()
 	}
 	// record transaction end time, override if already exists
-	if transaction.Type == TransactionEnd {
-		r.transactions[transaction.Name][TransactionEnd] = time.Now()
+	if transaction.Type == transactionEnd {
+		r.transactions[transaction.Name][transactionEnd] = time.Now()
 
 		// if transaction start time not exists, use testcase start time instead
-		if _, ok := r.transactions[transaction.Name][TransactionStart]; !ok {
-			r.transactions[transaction.Name][TransactionStart] = r.startTime
+		if _, ok := r.transactions[transaction.Name][transactionStart]; !ok {
+			r.transactions[transaction.Name][transactionStart] = r.startTime
 		}
 
 		// calculate transaction duration
-		duration := r.transactions[transaction.Name][TransactionEnd].Sub(
-			r.transactions[transaction.Name][TransactionStart])
+		duration := r.transactions[transaction.Name][transactionEnd].Sub(
+			r.transactions[transaction.Name][transactionStart])
 		stepResult.elapsed = duration.Milliseconds()
 		log.Info().Str("name", transaction.Name).Dur("elapsed", duration).Msg("transaction")
 	}
diff --git a/step.go b/step.go
index 4bfcc167..dc7b3bc3 100644
--- a/step.go
+++ b/step.go
@@ -178,7 +178,7 @@ func (s *StepRequest) CallRefCase(tc *TestCase) *StepTestCaseWithOptionalArgs {
 func (s *StepRequest) StartTransaction(name string) *StepTransaction {
 	s.step.Transaction = &Transaction{
 		Name: name,
-		Type: TransactionStart,
+		Type: transactionStart,
 	}
 	return &StepTransaction{
 		step: s.step,
@@ -189,7 +189,7 @@ func (s *StepRequest) StartTransaction(name string) *StepTransaction {
 func (s *StepRequest) EndTransaction(name string) *StepTransaction {
 	s.step.Transaction = &Transaction{
 		Name: name,
-		Type: TransactionEnd,
+		Type: transactionEnd,
 	}
 	return &StepTransaction{
 		step: s.step,