diff --git a/.github/workflows/go.yml b/.github/workflows/tests.yml
similarity index 100%
rename from .github/workflows/go.yml
rename to .github/workflows/tests.yml
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..fa92975
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.out
\ No newline at end of file
diff --git a/README.md b/README.md
index 22ab16a..cf5320d 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,8 @@
-# Ozon API Client
-A Ozon API client written in Golang
+# Ozon Seller API Client
+A Ozon Seller API client written in Golang
+
+[![Coverage Status](https://coveralls.io/repos/github/diPhantxm/ozon-api-client/badge.svg?branch=master)](https://coveralls.io/github/diPhantxm/ozon-api-client?branch=master)
+![example workflow](https://github.com/diPhantxm/ozon-api-client/actions/workflows/tests.yml/badge.svg)
 
 [Ozon](https://ozon.ru) is a marketplace for small and medium enterprises to launch and grow their businesses in Russia.
 
@@ -14,7 +17,7 @@ go get github.com/diphantxm/ozon-api-client
 ```
 A simple example on how to use this library:
 ```Golang
-package integrations
+package main
 
 import (
 	"fmt"
@@ -24,7 +27,7 @@ import (
 	"github.com/diphantxm/ozon-api-client/ozon"
 )
 
-func t() {
+func main() {
 	// Create a client with your Client-Id and Api-Key
 	// [Documentation]: https://docs.ozon.ru/api/seller/en/#tag/Auth
 	client := ozon.NewClient("my-client-id", "my-api-key")
@@ -42,5 +45,9 @@ func t() {
 		fmt.Printf("Barcode %s\n", d)
 	}
 }
+```
 
-```
\ No newline at end of file
+## Contribution
+If you need some endpoints ASAP, create an issue and list all the endpoints. I will add them to library soon.
+
+Or you can implement them and contribute to the project. Contribution to the project is welcome. 
\ No newline at end of file
diff --git a/client_test.go b/client_test.go
new file mode 100644
index 0000000..95f8382
--- /dev/null
+++ b/client_test.go
@@ -0,0 +1,68 @@
+package core
+
+import (
+	"net/http"
+	"testing"
+)
+
+type TestRequestRequest struct {
+	FirstField  string `json:"first_field"`
+	SecondField int32  `json:"second_field"`
+}
+
+type TestRequestResponse struct {
+	FirstField  string `json:"first_header"`
+	SecondField struct {
+		Key int32 `json:"key"`
+	} `json:"second_header"`
+	ThirdField []struct {
+		FirstElement string `json:"first_element"`
+	} `json:"third_header"`
+}
+
+func TestRequest(t *testing.T) {
+	tests := []struct {
+		statusCode int
+		headers    map[string]string
+		params     *TestRequestRequest
+		response   string
+	}{
+		{
+			http.StatusOK,
+			map[string]string{
+				"first_header":  "first-value",
+				"second_header": "second-value",
+			},
+			&TestRequestRequest{
+				FirstField:  "test",
+				SecondField: 123,
+			},
+			`{
+				"first_field": "first-value",
+				"second_field": {
+					"key": 12
+				},
+				"third_field": [
+					{
+						"first_element": "first-element-value"
+					}
+				]
+			}`,
+		},
+	}
+
+	for _, test := range tests {
+		c := NewMockClient(NewMockHttpHandler(test.statusCode, test.response, test.headers))
+
+		respStruct := &TestRequestResponse{}
+		resp, err := c.Request(http.MethodPost, "/", test.params, respStruct)
+
+		if err != nil {
+			t.Error(err)
+		}
+
+		if resp.StatusCode != test.statusCode {
+			t.Errorf("got wrong status code: got: %d, expected: %d", resp.StatusCode, test.statusCode)
+		}
+	}
+}
diff --git a/ozon/analytics_test.go b/ozon/analytics_test.go
index aa7acf9..9f0a058 100644
--- a/ozon/analytics_test.go
+++ b/ozon/analytics_test.go
@@ -14,6 +14,7 @@ func TestGetAnalyticsData(t *testing.T) {
 		params     *GetAnalyticsDataParams
 		response   string
 	}{
+		// Test ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -41,6 +42,16 @@ func TestGetAnalyticsData(t *testing.T) {
 				"timestamp": "2021-11-25 15:19:21"
 			}`,
 		},
+		{
+			// Test No Client-Id or Api-Key
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetAnalyticsDataParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -64,6 +75,7 @@ func TestGetStocksOnWarehouses(t *testing.T) {
 		params     *GetStocksOnWarehousesParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -87,6 +99,16 @@ func TestGetStocksOnWarehouses(t *testing.T) {
 				  ]
 				}
 			}`,
+		}, 
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetStocksOnWarehousesParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
 		},
 	}
 
diff --git a/ozon/fbo_test.go b/ozon/fbo_test.go
index 6df1078..46661a9 100644
--- a/ozon/fbo_test.go
+++ b/ozon/fbo_test.go
@@ -14,6 +14,7 @@ func TestGetFBOShipmentsList(t *testing.T) {
 		params     *GetFBOShipmentsListParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -115,6 +116,16 @@ func TestGetFBOShipmentsList(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetFBOShipmentsListParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/ozon/fbs_test.go b/ozon/fbs_test.go
index ec549d9..0874ce2 100644
--- a/ozon/fbs_test.go
+++ b/ozon/fbs_test.go
@@ -14,6 +14,7 @@ func TestListUnprocessedShipments(t *testing.T) {
 		params     *ListUnprocessedShipmentsParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -149,6 +150,16 @@ func TestListUnprocessedShipments(t *testing.T) {
 				}
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&ListUnprocessedShipmentsParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -172,6 +183,7 @@ func TestGetFBSShipmentsList(t *testing.T) {
 		params     *GetFBSShipmentsListParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -247,6 +259,16 @@ func TestGetFBSShipmentsList(t *testing.T) {
 				}
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetFBSShipmentsListParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -270,6 +292,7 @@ func TestPackOrder(t *testing.T) {
 		params     *PackOrderParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -295,6 +318,16 @@ func TestPackOrder(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&PackOrderParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/ozon/products_test.go b/ozon/products_test.go
index 7788f07..8126b7b 100644
--- a/ozon/products_test.go
+++ b/ozon/products_test.go
@@ -14,6 +14,7 @@ func TestGetStocksInfo(t *testing.T) {
 		params     *GetStocksInfoParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -51,27 +52,14 @@ func TestGetStocksInfo(t *testing.T) {
 				}
 			}`,
 		},
+		// Test No Client-Id or Api-Key
 		{
-			http.StatusBadRequest,
-			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
-			&GetStocksInfoParams{
-				Limit:  100,
-				LastId: "",
-				Filter: GetStocksInfoFilter{
-					OfferId:    "136834",
-					ProductId:  214887921,
-					Visibility: "ALL",
-				},
-			},
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetStocksInfoParams{},
 			`{
-				"code": 0,
-				"details": [
-				  {
-					"typeUrl": "string",
-					"value": "string"
-				  }
-				],
-				"message": "string"
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
 			}`,
 		},
 	}
@@ -97,6 +85,7 @@ func TestGetProductDetails(t *testing.T) {
 		params     *GetProductDetailsParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -227,21 +216,14 @@ func TestGetProductDetails(t *testing.T) {
 				}
 			  }`,
 		},
+		// Test No Client-Id or Api-Key
 		{
-			http.StatusBadRequest,
-			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
-			&GetProductDetailsParams{
-				ProductId: 137208233,
-			},
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetProductDetailsParams{},
 			`{
-				"code": 0,
-				"details": [
-				  {
-					"typeUrl": "string",
-					"value": "string"
-				  }
-				],
-				"message": "string"
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
 			}`,
 		},
 	}
@@ -267,6 +249,7 @@ func TestUpdateStocks(t *testing.T) {
 		params     *UpdateStocksParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -290,6 +273,16 @@ func TestUpdateStocks(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&UpdateStocksParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -313,6 +306,7 @@ func TestStocksInSellersWarehouse(t *testing.T) {
 		params     *StocksInSellersWarehouseParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -332,6 +326,16 @@ func TestStocksInSellersWarehouse(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&StocksInSellersWarehouseParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -355,6 +359,7 @@ func TestUpdatePrices(t *testing.T) {
 		params     *UpdatePricesParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -381,6 +386,16 @@ func TestUpdatePrices(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&UpdatePricesParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -404,6 +419,7 @@ func TestUpdateQuantityStockProducts(t *testing.T) {
 		params     *UpdateQuantityStockProductsParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -429,6 +445,16 @@ func TestUpdateQuantityStockProducts(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&UpdateQuantityStockProductsParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -452,6 +478,7 @@ func TestCreateOrUpdateProduct(t *testing.T) {
 		params     *CreateOrUpdateProductParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -533,6 +560,16 @@ func TestCreateOrUpdateProduct(t *testing.T) {
 				}
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&CreateOrUpdateProductParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -556,6 +593,7 @@ func TestGetListOfProducts(t *testing.T) {
 		params     *GetListOfProductsParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -581,6 +619,16 @@ func TestGetListOfProducts(t *testing.T) {
 				}
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetListOfProductsParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/ozon/promotions_test.go b/ozon/promotions_test.go
index b75c369..35b98b8 100644
--- a/ozon/promotions_test.go
+++ b/ozon/promotions_test.go
@@ -13,6 +13,7 @@ func TestGetAvailablePromotions(t *testing.T) {
 		headers    map[string]string
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -39,6 +40,15 @@ func TestGetAvailablePromotions(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/ozon/rating_test.go b/ozon/rating_test.go
index 360d8d9..da0a1e1 100644
--- a/ozon/rating_test.go
+++ b/ozon/rating_test.go
@@ -13,6 +13,7 @@ func TestGetCurrentRatingInfo(t *testing.T) {
 		headers    map[string]string
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -41,6 +42,15 @@ func TestGetCurrentRatingInfo(t *testing.T) {
 				"premium": true
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
@@ -64,6 +74,7 @@ func TestGetRatingInfoForPeriod(t *testing.T) {
 		params     *GetSellerRatingInfoForPeriodParams
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -108,6 +119,16 @@ func TestGetRatingInfoForPeriod(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			&GetSellerRatingInfoForPeriodParams{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/ozon/warehouses_test.go b/ozon/warehouses_test.go
index 7c652d5..b90b8b8 100644
--- a/ozon/warehouses_test.go
+++ b/ozon/warehouses_test.go
@@ -13,6 +13,7 @@ func TestGetListOfWarehouses(t *testing.T) {
 		headers    map[string]string
 		response   string
 	}{
+		// Test Ok
 		{
 			http.StatusOK,
 			map[string]string{"Client-Id": "my-client-id", "Api-Key": "my-api-key"},
@@ -41,6 +42,15 @@ func TestGetListOfWarehouses(t *testing.T) {
 				]
 			}`,
 		},
+		// Test No Client-Id or Api-Key
+		{
+			http.StatusUnauthorized,
+			map[string]string{},
+			`{
+				"code": 16,
+				"message": "Client-Id and Api-Key headers are required"
+			}`,
+		},
 	}
 
 	for _, test := range tests {