diff --git a/core/healthcheck/counter_test.go b/core/healthcheck/counter_test.go
new file mode 100644
index 0000000..06f51d5
--- /dev/null
+++ b/core/healthcheck/counter_test.go
@@ -0,0 +1,122 @@
+package healthcheck
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type AtomicCounterTest struct {
+	suite.Suite
+}
+
+func TestAtomicCounter(t *testing.T) {
+	suite.Run(t, new(AtomicCounterTest))
+}
+
+func (t *AtomicCounterTest) new() Counter {
+	return NewAtomicCounter("test")
+}
+
+func (t *AtomicCounterTest) Test_Name() {
+	t.Assert().Equal("test", t.new().Name())
+}
+
+func (t *AtomicCounterTest) Test_SetName() {
+	c := t.new()
+	c.SetName("new")
+	t.Assert().Equal("new", c.Name())
+}
+
+func (t *AtomicCounterTest) Test_HitSuccess() {
+	c := t.new()
+	c.HitSuccess()
+	t.Assert().Equal(uint32(1), c.TotalSucceeded())
+
+	c.Failed("test")
+	c.FailureProcessed()
+	c.HitSuccess()
+	t.Assert().Equal(uint32(2), c.TotalSucceeded())
+	t.Assert().False(c.IsFailed())
+	t.Assert().False(c.IsFailureProcessed())
+	t.Assert().Equal("", c.Message())
+}
+
+func (t *AtomicCounterTest) Test_HitFailure() {
+	c := t.new()
+	c.HitFailure()
+	t.Assert().Equal(uint32(1), c.TotalFailed())
+	c.HitFailure()
+	t.Assert().Equal(uint32(2), c.TotalFailed())
+}
+
+func (t *AtomicCounterTest) Test_Failed() {
+	c := t.new()
+	t.Require().False(c.IsFailed())
+	t.Require().Equal("", c.Message())
+
+	c.Failed("message")
+	t.Assert().True(c.IsFailed())
+	t.Assert().Equal("message", c.Message())
+}
+
+func (t *AtomicCounterTest) Test_CountersProcessed() {
+	c := t.new()
+	t.Require().False(c.IsCountersProcessed())
+
+	c.CountersProcessed()
+	t.Assert().True(c.IsCountersProcessed())
+
+	c.ClearCountersProcessed()
+	t.Assert().False(c.IsCountersProcessed())
+}
+
+func (t *AtomicCounterTest) Test_FlushCounters() {
+	c := t.new()
+	c.HitSuccess()
+	t.Require().Equal(uint32(1), c.TotalSucceeded())
+
+	c.FlushCounters()
+	t.Assert().Equal(uint32(1), c.TotalSucceeded())
+
+	c.(*AtomicCounter).timestamp.Store(time.Now().Add(-(DefaultResetPeriod + time.Second)))
+	c.FlushCounters()
+	t.Assert().Equal(uint32(0), c.TotalSucceeded())
+}
+
+func (t *AtomicCounterTest) Test_Concurrency() {
+	c := t.new()
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		for i := 0; i < 1000; i++ {
+			c.HitSuccess()
+		}
+		wg.Done()
+	}()
+	go func() {
+		for i := 0; i < 500; i++ {
+			// this delay will ensure that failure is being called after success.
+			// technically, both have been executed concurrently because first 399 calls will not be delayed.
+			if i > 399 {
+				time.Sleep(time.Microsecond)
+			}
+			if i > 400 {
+				c.Failed("total failure")
+				continue
+			}
+			c.HitFailure()
+		}
+		c.FailureProcessed()
+		wg.Done()
+	}()
+	wg.Wait()
+
+	t.Assert().Equal(uint32(1000), c.TotalSucceeded())
+	t.Assert().Equal(uint32(401), c.TotalFailed())
+	t.Assert().True(c.IsFailed())
+	t.Assert().True(c.IsFailureProcessed())
+	t.Assert().Equal("total failure", c.Message())
+}
diff --git a/core/healthcheck/notifier_test.go b/core/healthcheck/notifier_test.go
new file mode 100644
index 0000000..bb3aee1
--- /dev/null
+++ b/core/healthcheck/notifier_test.go
@@ -0,0 +1,65 @@
+package healthcheck
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"testing"
+
+	retailcrm "github.com/retailcrm/api-client-go/v2"
+	"github.com/retailcrm/mg-transport-core/v2/core/util/testutil"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/h2non/gock.v1"
+)
+
+func TestDefaultNotifyFunc(t *testing.T) {
+	apiURL := "https://test.retailcrm.pro"
+	apiKey := "key"
+	msg := "Notification"
+
+	data, err := json.Marshal(retailcrm.NotificationsSendRequest{
+		UserGroups: []retailcrm.UserGroupType{retailcrm.UserGroupSuperadmins},
+		Type:       retailcrm.NotificationTypeError,
+		Message:    msg,
+	})
+	require.NoError(t, err)
+
+	defer gock.Off()
+	gock.New(apiURL).
+		Post("/api/v5/notifications/send").
+		BodyString(url.Values{"notification": {string(data)}}.Encode()).
+		Reply(http.StatusOK).
+		JSON(retailcrm.SuccessfulResponse{Success: true})
+
+	assert.NoError(t, DefaultNotifyFunc(apiURL, apiKey, msg))
+	testutil.AssertNoUnmatchedRequests(t)
+}
+
+func TestDefaultNotifyFunc_Error(t *testing.T) {
+	apiURL := "https://test.retailcrm.pro"
+	apiKey := "key"
+	msg := "Notification"
+
+	data, err := json.Marshal(retailcrm.NotificationsSendRequest{
+		UserGroups: []retailcrm.UserGroupType{retailcrm.UserGroupSuperadmins},
+		Type:       retailcrm.NotificationTypeError,
+		Message:    msg,
+	})
+	require.NoError(t, err)
+
+	defer gock.Off()
+	gock.New(apiURL).
+		Post("/api/v5/notifications/send").
+		BodyString(url.Values{"notification": {string(data)}}.Encode()).
+		Reply(http.StatusForbidden).
+		JSON(retailcrm.ErrorResponse{
+			SuccessfulResponse: retailcrm.SuccessfulResponse{Success: false},
+			ErrorMessage:       "Forbidden",
+		})
+
+	err = DefaultNotifyFunc(apiURL, apiKey, msg)
+	assert.Error(t, err)
+	assert.Equal(t, "Forbidden", err.Error())
+	testutil.AssertNoUnmatchedRequests(t)
+}
diff --git a/core/healthcheck/processor.go b/core/healthcheck/processor.go
index ddfb13e..4e213cc 100644
--- a/core/healthcheck/processor.go
+++ b/core/healthcheck/processor.go
@@ -1,13 +1,9 @@
 package healthcheck
 
 import (
-	"errors"
-
 	"github.com/retailcrm/mg-transport-core/v2/core/logger"
 )
 
-var ErrNoConnection = errors.New("no connection")
-
 const (
 	// DefaultMinRequests is a default minimal threshold of total requests. If Counter has less than this amount of requests
 	// total, it will be skipped because it can trigger false alerts otherwise.
diff --git a/core/healthcheck/processor_test.go b/core/healthcheck/processor_test.go
new file mode 100644
index 0000000..c6d30a9
--- /dev/null
+++ b/core/healthcheck/processor_test.go
@@ -0,0 +1,363 @@
+package healthcheck
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/retailcrm/mg-transport-core/v2/core/util/testutil"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/suite"
+)
+
+type CounterProcessorTest struct {
+	suite.Suite
+	apiURL string
+	apiKey string
+	lang   string
+}
+
+func TestCounterProcessor(t *testing.T) {
+	suite.Run(t, new(CounterProcessorTest))
+}
+
+func (t *CounterProcessorTest) SetupSuite() {
+	t.apiURL = "https://test.retailcrm.pro"
+	t.apiKey = "key"
+	t.lang = "en"
+}
+
+func (t *CounterProcessorTest) localizer() NotifyMessageLocalizer {
+	loc := &localizerMock{}
+	loc.On("SetLocale", mock.AnythingOfType("string")).Return()
+	loc.On("GetLocalizedTemplateMessage",
+		mock.AnythingOfType("string"), mock.Anything).Return(
+		func(msg string, tpl map[string]interface{}) string {
+			data, err := json.Marshal(tpl)
+			if err != nil {
+				panic(err)
+			}
+			return fmt.Sprintf("%s [%s]", msg, string(data))
+		})
+	return loc
+}
+
+func (t *CounterProcessorTest) new(
+	nf NotifyFunc, pr ConnectionDataProvider, noLocalizer ...bool) (Processor, testutil.BufferedLogger) {
+	loc := t.localizer()
+	if len(noLocalizer) > 0 && noLocalizer[0] {
+		loc = nil
+	}
+
+	log := testutil.NewBufferedLogger()
+	return CounterProcessor{
+		Localizer:              loc,
+		Logger:                 log,
+		Notifier:               nf,
+		ConnectionDataProvider: pr,
+		Error:                  "default error",
+		FailureThreshold:       DefaultFailureThreshold,
+		MinRequests:            DefaultMinRequests,
+		Debug:                  true,
+	}, log
+}
+
+func (t *CounterProcessorTest) notifier(err ...error) *notifierMock {
+	if len(err) > 0 && err[0] != nil {
+		return &notifierMock{err: err[0]}
+	}
+	return &notifierMock{}
+}
+
+func (t *CounterProcessorTest) provider(notFound ...bool) ConnectionDataProvider {
+	if len(notFound) > 0 && notFound[0] {
+		return func(id int) (apiURL, apiKey, lang string, exists bool) {
+			return "", "", "", false
+		}
+	}
+	return func(id int) (apiURL, apiKey, lang string, exists bool) {
+		return t.apiURL, t.apiKey, t.lang, true
+	}
+}
+
+func (t *CounterProcessorTest) counter() mockedCounter {
+	return &counterMock{}
+}
+
+func (t *CounterProcessorTest) Test_FailureProcessed() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(true)
+	c.On("IsFailureProcessed").Return(true)
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(), "skipping counter id=1 because its failure is already processed")
+}
+
+func (t *CounterProcessorTest) Test_CounterFailed_CannotFindConnection() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider(true))
+	c := t.counter()
+	c.On("IsFailed").Return(true)
+	c.On("IsFailureProcessed").Return(false)
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(), "cannot find connection data for counter id=1")
+}
+
+func (t *CounterProcessorTest) Test_CounterFailed_ErrWhileNotifying() {
+	n := t.notifier(errors.New("http status code: 500"))
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(true)
+	c.On("IsFailureProcessed").Return(false)
+	c.On("Message").Return("error message")
+	c.On("FailureProcessed").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(), "cannot send notification for counter id=1: http status code: 500 (message: error message)")
+	t.Assert().Equal(t.apiURL, n.apiURL)
+	t.Assert().Equal(t.apiKey, n.apiKey)
+	t.Assert().Equal("error message", n.message)
+}
+
+func (t *CounterProcessorTest) Test_CounterFailed_SentNotification() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(true)
+	c.On("IsFailureProcessed").Return(false)
+	c.On("Message").Return("error message")
+	c.On("FailureProcessed").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Empty(log.String())
+	t.Assert().Equal(t.apiURL, n.apiURL)
+	t.Assert().Equal(t.apiKey, n.apiKey)
+	t.Assert().Equal("error message", n.message)
+}
+
+func (t *CounterProcessorTest) Test_TooFewRequests() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(0))
+	c.On("TotalSucceeded").Return(uint32(DefaultMinRequests - 1))
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(),
+		fmt.Sprintf("skipping counter id=%d because it has fewer than %d requests", 1, DefaultMinRequests))
+}
+
+func (t *CounterProcessorTest) Test_ThresholdNotPassed() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(20))
+	c.On("TotalSucceeded").Return(uint32(80))
+	c.On("ClearCountersProcessed").Return()
+	c.On("FlushCounters").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Empty(log.String())
+	t.Assert().Empty(n.message)
+}
+
+func (t *CounterProcessorTest) Test_ThresholdPassed_AlreadyProcessed() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(21))
+	c.On("TotalSucceeded").Return(uint32(79))
+	c.On("IsCountersProcessed").Return(true)
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Empty(log.String())
+	t.Assert().Empty(n.message)
+}
+
+func (t *CounterProcessorTest) Test_ThresholdPassed_NoConnectionFound() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider(true))
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(21))
+	c.On("TotalSucceeded").Return(uint32(79))
+	c.On("IsCountersProcessed").Return(false)
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(), "cannot find connection data for counter id=1")
+	t.Assert().Empty(n.message)
+}
+
+func (t *CounterProcessorTest) Test_ThresholdPassed_NotifyingError() {
+	n := t.notifier(errors.New("unknown error"))
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(21))
+	c.On("TotalSucceeded").Return(uint32(79))
+	c.On("IsCountersProcessed").Return(false)
+	c.On("Name").Return("MockedCounter")
+	c.On("Message").Return("")
+	c.On("CountersProcessed").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Contains(log.String(), "cannot send notification for counter id=1: unknown error (message: )")
+	t.Assert().Equal(`default error [{"Name":"MockedCounter"}]`, n.message)
+}
+
+func (t *CounterProcessorTest) Test_ThresholdPassed_NotificationSent() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider())
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(21))
+	c.On("TotalSucceeded").Return(uint32(79))
+	c.On("IsCountersProcessed").Return(false)
+	c.On("Name").Return("MockedCounter")
+	c.On("CountersProcessed").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Empty(log.String())
+	t.Assert().Equal(`default error [{"Name":"MockedCounter"}]`, n.message)
+}
+
+func (t *CounterProcessorTest) Test_ThresholdPassed_NotificationSent_NoLocalizer() {
+	n := t.notifier()
+	p, log := t.new(n.Notify, t.provider(), true)
+	c := t.counter()
+	c.On("IsFailed").Return(false)
+	c.On("TotalFailed").Return(uint32(21))
+	c.On("TotalSucceeded").Return(uint32(79))
+	c.On("IsCountersProcessed").Return(false)
+	c.On("Name").Return("MockedCounter")
+	c.On("CountersProcessed").Return()
+
+	p.Process(1, c)
+	c.AssertExpectations(t.T())
+	t.Assert().Empty(log.String())
+	t.Assert().Equal(`default error`, n.message)
+}
+
+type localizerMock struct {
+	mock.Mock
+}
+
+func (l *localizerMock) SetLocale(lang string) {
+	l.Called(lang)
+}
+
+func (l *localizerMock) GetLocalizedTemplateMessage(messageID string, templateData map[string]interface{}) string {
+	args := l.Called(messageID, templateData)
+	if fn, ok := args.Get(0).(func(string, map[string]interface{}) string); ok {
+		return fn(messageID, templateData)
+	}
+	return args.String(0)
+}
+
+type mockedCounter interface {
+	Counter
+	On(methodName string, arguments ...interface{}) *mock.Call
+	AssertExpectations(t mock.TestingT) bool
+}
+
+type counterMock struct {
+	mock.Mock
+}
+
+func (cm *counterMock) Name() string {
+	args := cm.Called()
+	return args.String(0)
+}
+
+func (cm *counterMock) SetName(name string) {
+	cm.Called(name)
+}
+
+func (cm *counterMock) HitSuccess() {
+	cm.Called()
+}
+
+func (cm *counterMock) HitFailure() {
+	cm.Called()
+}
+
+func (cm *counterMock) TotalSucceeded() uint32 {
+	args := cm.Called()
+	return args.Get(0).(uint32)
+}
+
+func (cm *counterMock) TotalFailed() uint32 {
+	args := cm.Called()
+	return args.Get(0).(uint32)
+}
+
+func (cm *counterMock) Message() string {
+	args := cm.Called()
+	return args.String(0)
+}
+
+func (cm *counterMock) IsFailed() bool {
+	args := cm.Called()
+	return args.Bool(0)
+}
+
+func (cm *counterMock) Failed(message string) {
+	cm.Called(message)
+}
+
+func (cm *counterMock) IsFailureProcessed() bool {
+	args := cm.Called()
+	return args.Bool(0)
+}
+
+func (cm *counterMock) IsCountersProcessed() bool {
+	args := cm.Called()
+	return args.Bool(0)
+}
+
+func (cm *counterMock) FailureProcessed() {
+	cm.Called()
+}
+
+func (cm *counterMock) CountersProcessed() {
+	cm.Called()
+}
+
+func (cm *counterMock) ClearCountersProcessed() {
+	cm.Called()
+}
+
+func (cm *counterMock) FlushCounters() {
+	cm.Called()
+}
+
+type notifierMock struct {
+	apiURL  string
+	apiKey  string
+	message string
+	err     error
+}
+
+func (n *notifierMock) Notify(apiURL, apiKey, msg string) error {
+	n.apiURL = apiURL
+	n.apiKey = apiKey
+	n.message = msg
+	return n.err
+}
diff --git a/core/healthcheck/storage_test.go b/core/healthcheck/storage_test.go
new file mode 100644
index 0000000..ce4919d
--- /dev/null
+++ b/core/healthcheck/storage_test.go
@@ -0,0 +1,68 @@
+package healthcheck
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type SyncMapStorageTest struct {
+	suite.Suite
+	storage Storage
+}
+
+func TestSyncMapStorage(t *testing.T) {
+	suite.Run(t, new(SyncMapStorageTest))
+}
+
+func (t *SyncMapStorageTest) SetupSuite() {
+	t.storage = NewSyncMapStorage(NewAtomicCounter)
+}
+
+func (t *SyncMapStorageTest) Test_Get() {
+	counter := t.storage.Get(1, "Name")
+	t.Assert().NotNil(counter)
+	t.Assert().IsType(&AtomicCounter{}, counter)
+	t.Assert().Equal("Name", counter.Name())
+
+	newCounter := t.storage.Get(1, "New Name")
+	t.Assert().Equal(counter, newCounter)
+	t.Assert().Equal("New Name", newCounter.Name())
+}
+
+func (t *SyncMapStorageTest) Test_Process() {
+	var wg sync.WaitGroup
+	wg.Add(1)
+	t.storage.Process(storageCallbackProcessor{callback: func(id int, counter Counter) bool {
+		t.Assert().Equal(1, id)
+		t.Assert().Equal("New Name", counter.Name())
+		wg.Done()
+		return false
+	}})
+
+	wg.Wait()
+}
+
+func (t *SyncMapStorageTest) Test_Remove() {
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fail("unexpected panic:", r)
+		}
+	}()
+	t.storage.Remove(0)
+	t.storage.Remove(-1)
+	t.storage.Remove(1)
+	t.storage.Process(storageCallbackProcessor{callback: func(id int, counter Counter) bool {
+		t.Fail("did not expect any items:", id, counter)
+		return false
+	}})
+}
+
+type storageCallbackProcessor struct {
+	callback func(id int, counter Counter) bool
+}
+
+func (p storageCallbackProcessor) Process(id int, counter Counter) bool {
+	return p.callback(id, counter)
+}
diff --git a/go.mod b/go.mod
index 5303606..d8afc1b 100644
--- a/go.mod
+++ b/go.mod
@@ -69,6 +69,7 @@ require (
 	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
 	github.com/ugorji/go/codec v1.2.6 // indirect
 	golang.org/x/crypto v0.0.0-20210921155107-089bfa567519 // indirect
 	golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac // indirect
diff --git a/go.sum b/go.sum
index a04db1a..6d8dfcd 100644
--- a/go.sum
+++ b/go.sum
@@ -385,6 +385,7 @@ github.com/spf13/viper v1.3.2/go.mod h1:ZiWeW+zYFKm7srdB9IoDzzZXaJaI5eL9QjNiN/DM
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
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