You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: transformer_test.go
    path of file: ./repos/magistrala/pkg/transformers/json
    
    the code of the file until where you have to start completion: // Copyright (c) Abstract Machines
// SPDX-License-Identifier: Apache-2.0

package json_test

import (
	"fmt"
	"testing"
	"time"

	"github.com/absmach/magistrala/pkg/errors"
	"github.com/absmach/magistrala/pkg/messaging"
	"github.com/absmach/magistrala/pkg/transformers/json"
	"github.com/stretchr/testify/assert"
)

const (
	validPayload     = `{"key1": "val1", "key2": 123, "key3": "val3", "key4": {"key5": "val5"}}`
	tsPayload        = `{"custom_ts_key": "1638310819", "key1": "val1", "key2": 123, "key3": "val3", "key4": {"key5": "val5"}}`
	microsPayload    = `{"custom_ts_micro_key": "1638310819000000", "key1": "val1", "key2": 123, "key3": "val3", "key4": {"key5": "val5"}}`
	invalidTSPayload = `{"custom_ts_key": "abc", "key1": "val1", "key2": 123, "key3": "val3", "key4": {"key5": "val5"}}`
	listPayload      = `[{"key1": "val1", "key2": 123, "keylist3": "val3", "key4": {"key5": "val5"}}, {"key1": "val1", "key2": 123, "key3": "val3", "key4": {"key5": "val5"}}]`
	invalidPayload   = `{"key1": }`
)

func TestTransformJSON(t *testing.T) {
	now := time.Now().Unix()
	ts := []json.TimeField{
		{
			FieldName:   "custom_ts_key",
			FieldFormat: "unix",
		}, {
			FieldName:   "custom_ts_micro_key",
			FieldFormat: "unix_us",
		},
	}
	tr := json.New(ts)
	msg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(validPayload),
		Created:   now,
	}
	invalid := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(invalidPayload),
		Created:   now,
	}

	listMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(listPayload),
		Created:   now,
	}

	tsMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(tsPayload),
		Created:   now,
	}

	microsMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(microsPayload),
		Created:   now,
	}

	invalidFmt := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(validPayload),
		Created:   now,
	}

	invalidTimeField := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(invalidTSPayload),
		Created:   now,
	}

	jsonMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   msg.Created,
				Payload: map[string]interface{}{
					"key1": "val1",
					"key2": float64(123),
					"key3": "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	jsonTSMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   int64(1638310819000000000),
				Payload: map[string]interface{}{
					"custom_ts_key": "1638310819",
					"key1":          "val1",
					"key2":          float64(123),
					"key3":          "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	jsonMicrosMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.S
    
func TestTransformJSON(t *testing.T) {
	now := time.Now().Unix()
	ts := []json.TimeField{
		{
			FieldName:   "custom_ts_key",
			FieldFormat: "unix",
		}, {
			FieldName:   "custom_ts_micro_key",
			FieldFormat: "unix_us",
		},
	}
	tr := json.New(ts)
	msg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(validPayload),
		Created:   now,
	}
	invalid := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(invalidPayload),
		Created:   now,
	}

	listMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(listPayload),
		Created:   now,
	}

	tsMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(tsPayload),
		Created:   now,
	}

	microsMsg := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(microsPayload),
		Created:   now,
	}

	invalidFmt := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(validPayload),
		Created:   now,
	}

	invalidTimeField := messaging.Message{
		Channel:   "channel-1",
		Subtopic:  "subtopic-1",
		Publisher: "publisher-1",
		Protocol:  "protocol",
		Payload:   []byte(invalidTSPayload),
		Created:   now,
	}

	jsonMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   msg.Created,
				Payload: map[string]interface{}{
					"key1": "val1",
					"key2": float64(123),
					"key3": "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	jsonTSMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   int64(1638310819000000000),
				Payload: map[string]interface{}{
					"custom_ts_key": "1638310819",
					"key1":          "val1",
					"key2":          float64(123),
					"key3":          "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	jsonMicrosMsgs := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   int64(1638310819000000000),
				Payload: map[string]interface{}{
					"custom_ts_micro_key": "1638310819000000",
					"key1":                "val1",
					"key2":                float64(123),
					"key3":                "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	listJSON := json.Messages{
		Data: []json.Message{
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   msg.Created,
				Payload: map[string]interface{}{
					"key1":     "val1",
					"key2":     float64(123),
					"keylist3": "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
			{
				Channel:   msg.Channel,
				Subtopic:  msg.Subtopic,
				Publisher: msg.Publisher,
				Protocol:  msg.Protocol,
				Created:   msg.Created,
				Payload: map[string]interface{}{
					"key1": "val1",
					"key2": float64(123),
					"key3": "val3",
					"key4": map[string]interface{}{
						"key5": "val5",
					},
				},
			},
		},
		Format: msg.Subtopic,
	}

	cases := []struct {
		desc string
		msg  *messaging.Message
		json interface{}
		err  error
	}{
		{
			desc: "test transform JSON",
			msg:  &msg,
			json: jsonMsgs,
			err:  nil,
		},
		{
			desc: "test transform JSON with an invalid subtopic",
			msg:  &invalidFmt,
			json: nil,
			err:  json.ErrTransform,
		},
		{
			desc: "test transform JSON array",
			msg:  &listMsg,
			json: listJSON,
			err:  nil,
		},
		{
			desc: "test transform JSON with invalid payload",
			msg:  &invalid,
			json: nil,
			err:  json.ErrTransform,
		},
		{
			desc: "test transform JSON with timestamp transformation",
			msg:  &tsMsg,
			json: jsonTSMsgs,
			err:  nil,
		},
		{
			desc: "test transform JSON with timestamp transformation in micros",
			msg:  &microsMsg,
			json: jsonMicrosMsgs,
			err:  nil,
		},
		{
			desc: "test transform JSON with invalid timestamp transformation in micros",
			msg:  &invalidTimeField,
			json: nil,
			err:  json.ErrInvalidTimeField,
		},
	}

	for _, tc := range cases {
		m, err := tr.Transform(tc.msg)
		assert.Equal(t, tc.json, m, fmt.Sprintf("%s got incorrect json response from Transform()", tc.desc))
		assert.True(t, errors.Contains(err, tc.err), fmt.Sprintf("%s expected %s, got %s", tc.desc, tc.err, err))
	}
}