pool: implemented Role Stringer interface

implemented Role Stringer interface for human-readable printing

Author: Maksim Konovalov

CHANGELOG.md

@@ -9,6 +9,7 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 ## [Unreleased]
 
 ### Added
+- Implemented Stringer interface for pool.Role type (#405).
 - Add err log to `ConnectionPool.Add()` in case, when unable to establish 
   connection and ctx is not canceled; 
   also added logs for error case of `ConnectionPool.tryConnect()` calls in 

pool/const.go

@@ -35,3 +35,14 @@ const (
 	MasterRole              // The instance is read-write mode.
 	ReplicaRole             // The instance is in read-only mode.
 )
+
+var role2String = map[Role]string{
+	UnknownRole: "unknown",
+	MasterRole:  "master",
+	ReplicaRole: "replica",
+}
+
+// String is implementation of the Stringer interface for human readability when printing a value
+func (r Role) String() string {
+	return role2String[r]
+}

pool/const_test.go

@@ -0,0 +1,15 @@
+package pool
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRole_String(t *testing.T) {
+	// Checking that print is non-number(len = 1 ) Role
+	require.True(t, len(fmt.Sprintf("%v", UnknownRole)) > 1)
+	require.True(t, len(fmt.Sprintf("%v", MasterRole)) > 1)
+	require.True(t, len(fmt.Sprintf("%v", ReplicaRole)) > 1)
+}