diff --git a/utils/json_codec_test.go b/utils/json_codec_test.go
new file mode 100644
index 000000000..791a68b1e
--- /dev/null
+++ b/utils/json_codec_test.go
@@ -0,0 +1,202 @@
+/*
+Real-time Online/Offline Charging System (OCS) for Telecom & ISP environments
+Copyright (C) ITsysCOM GmbH
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>
+*/
+
+package utils
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/rpc"
+	"testing"
+)
+
+func TestNewCustomJSONServerCodec(t *testing.T) {
+
+	reader, writer := io.Pipe()
+
+	codec := NewCustomJSONServerCodec(struct {
+		io.Reader
+		io.Writer
+		io.Closer
+	}{Reader: reader, Writer: writer, Closer: writer})
+
+	c := codec.(*jsonServerCodec)
+
+	if c.dec == nil {
+		t.Error("Decoder is nil")
+	}
+	if c.enc == nil {
+		t.Error("Encoder is nil")
+	}
+	if c.c == nil {
+		t.Error("Connection is nil")
+	}
+	if c.pending == nil {
+		t.Error("Pending map is nil")
+	}
+
+	writer.Close()
+}
+
+func TestJSONCodecReset(t *testing.T) {
+
+	r := serverRequest{
+		Method:  "test",
+		Params:  &json.RawMessage{},
+		Id:      &json.RawMessage{},
+		isApier: false,
+	}
+
+	r.reset()
+
+	if r.Method != "" {
+		t.Error("Method didn't clear")
+	}
+	if r.Params != nil {
+		t.Error("Params didn't clear")
+	}
+	if r.Id != nil {
+		t.Error("Id didn't clear")
+	}
+}
+
+type bufferClose struct {
+	*bytes.Buffer
+}
+
+func (b *bufferClose) Close() error {
+	return nil
+}
+
+func TestJSONCodecReadRequestHeader2(t *testing.T) {
+	tests := []struct {
+		name  string
+		write []byte
+		exp   error
+	}{
+		{
+			name: "ValidRequest",
+			write: []byte(`{
+				"method": "APIerSv1.RemTP",
+				"params": [{
+					"TPid": "test"
+				}],
+				"id": 0
+			}`),
+			exp: nil,
+		},
+		{
+			name:  "InvalidRequest",
+			write: []byte("test"),
+			exp:   fmt.Errorf("invalid character 'e' in literal true (expecting 'r')"),
+		},
+		{
+			name: "ValidApierRequest",
+			write: []byte(`{
+				"method": "ApierV.Method",
+				"params": [{
+					"TPid": "test"
+				}],
+				"id": 0
+			}`),
+			exp: nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			conn := &bufferClose{
+				Buffer: &bytes.Buffer{},
+			}
+			s := NewCustomJSONServerCodec(conn)
+
+			rr := rpc.Request{
+				ServiceMethod: "Service.Method",
+				Seq:           1,
+			}
+
+			conn.Write(tt.write)
+
+			err := s.ReadRequestHeader(&rr)
+			if err != nil {
+				if err.Error() != tt.exp.Error() {
+					t.Errorf("Received an error: %v", err)
+				}
+			}
+		})
+	}
+}
+
+func TestJSONReadRequestBody(t *testing.T) {
+	tests := []struct{
+		name string
+		arg any 
+		exp error
+		params bool
+	}{
+		{
+			name: "nil argument",
+			arg: nil,
+			exp: nil,
+			params: false,
+		},
+		{
+			name: "check error missing param",
+			arg: "test",
+			exp: errMissingParams,
+			params: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			conn := &bufferClose{
+				Buffer: &bytes.Buffer{},
+			}
+			s := NewCustomJSONServerCodec(conn)
+			sj := s.(*jsonServerCodec)
+
+			if tt.params {
+				sj.req.Params = nil
+			}
+
+			err := s.ReadRequestBody(tt.arg)
+
+			if err != nil {
+				if err.Error() != tt.exp.Error() {
+					t.Errorf("recived %s, expected %s", err, tt.exp)
+				}
+			}
+		})
+	}
+}
+
+func TestJSONCodecClose(t *testing.T) {
+	conn := &bufferClose{
+		Buffer: &bytes.Buffer{},
+	}
+	s := NewCustomJSONServerCodec(conn)
+
+	err := s.Close()
+
+	if err != nil {
+		t.Errorf("unexpected error: %s", err)
+	}
+}
diff --git a/utils/value_formula_test.go b/utils/value_formula_test.go
index 2fee56cef..246bfe065 100644
--- a/utils/value_formula_test.go
+++ b/utils/value_formula_test.go
@@ -19,6 +19,7 @@ package utils
 
 import (
 	"encoding/json"
+	"errors"
 	"reflect"
 	"testing"
 	"time"
@@ -76,3 +77,134 @@ func TestValueFormulaParseBalanceFilterValue(t *testing.T) {
 		t.Errorf("Expecting: %+v, received: %+v", eVF, vf)
 	}
 }
+
+func TestValueFormulaString(t *testing.T) {
+	vf := ValueFormula{
+		Method: "test",
+		Params: map[string]any{"test": "val1"},
+		Static: 1.2,
+	}
+
+	rcv := vf.String()
+	exp := `{"Method":"test","Params":{"test":"val1"},"Static":1.2}`
+
+	if rcv != exp {
+		t.Errorf("recived %s, expected %s", rcv, exp)
+	}
+}
+
+func TestValueFormulaParseBalanceFilterValue2(t *testing.T) {
+	vf := ValueFormula{
+		Method: "test",
+		Params: map[string]any{"test": "val1"},
+		Static: 1.2,
+	}
+
+	type args struct {
+		tor string
+		val string
+	}
+
+	type exp struct {
+		val *ValueFormula
+		err error
+	}
+	tests := []struct {
+		name string
+		args args
+		exp  exp
+	}{
+		{
+			name: "json unmarshal error case",
+			args: args{tor: "*voice", val: "test"},
+			exp:  exp{val: nil, err: errors.New("Invalid value: " + "test")},
+		},
+		{
+			name: "json unmarshal case",
+			args: args{tor: "*voice", val: `{"Method":"test","Params":{"test":"val1"},"Static":1.2}`},
+			exp:  exp{val: &vf, err: nil},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rcv, err := ParseBalanceFilterValue(tt.args.tor, tt.args.val)
+
+			if err != nil {
+				if err.Error() != tt.exp.err.Error() {
+					t.Fatalf("recived %s, expected %s", err, tt.exp.err)
+				}
+			}
+
+			if !reflect.DeepEqual(rcv, tt.exp.val) {
+				t.Errorf("recived %s, expected %s", rcv, tt.exp.val)
+			}
+		})
+	}
+}
+
+func TestValueFormulaIncremetalFormula(t *testing.T) {
+	now := time.Now()
+
+	tests := []struct {
+		name string
+		arg  map[string]any
+		exp  float64
+	}{
+		{
+			name: "keys not found",
+			arg:  map[string]any{},
+			exp:  0.0,
+		},
+		{
+			name: "units is not a float64",
+			arg:  map[string]any{"Units": "test", "Interval": "test", "Increment": "test"},
+			exp:  0.0,
+		},
+		{
+			name: "type []byte",
+			arg:  map[string]any{"Units": 1.2, "Interval": []byte{1, 2}, "Increment": []byte{1, 2}},
+			exp:  0.0,
+		},
+		{
+			name: "default interval",
+			arg:  map[string]any{"Units": 1.2, "Interval": 1, "Increment": 1},
+			exp:  0.0,
+		},
+		{
+			name: "default increment",
+			arg:  map[string]any{"Units": 1.2, "Interval": []byte{1, 2}, "Increment": 1},
+			exp:  0.0,
+		},
+		{
+			name: "hour day",
+			arg:  map[string]any{"Units": 1.5, "Interval": "day", "Increment": "hour"},
+			exp:  1.5 / 24,
+		},
+		{
+			name: "hour month",
+			arg:  map[string]any{"Units": 1.5, "Interval": "month", "Increment": "hour"},
+			exp:  1.5 / (DaysInMonth(now.Year(), now.Month()) * 24),
+		},
+		{
+			name: "hour year",
+			arg:  map[string]any{"Units": 1.5, "Interval": "year", "Increment": "hour"},
+			exp:  1.5 / (DaysInYear(now.Year()) * 24),
+		},
+		{
+			name: "minute hour",
+			arg:  map[string]any{"Units": 1.5, "Interval": "hour", "Increment": "minute"},
+			exp:  1.5 / 60,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rcv := incrementalFormula(tt.arg)
+
+			if rcv != tt.exp {
+				t.Errorf("recived %v, expected %v", rcv, tt.exp)
+			}
+		})
+	}
+}