diff --git a/src/__tests__/lib/api/BulkSending.test.ts b/src/__tests__/lib/api/BulkSending.test.ts
new file mode 100644
index 0000000..66cb95a
--- /dev/null
+++ b/src/__tests__/lib/api/BulkSending.test.ts
@@ -0,0 +1,146 @@
+import axios from "axios";
+import AxiosMockAdapter from "axios-mock-adapter";
+
+import BulkSendingAPI from "../../../lib/api/BulkSending";
+import handleSendingError from "../../../lib/axios-logger";
+import MailtrapError from "../../../lib/MailtrapError";
+
+import CONFIG from "../../../config";
+
+const { CLIENT_SETTINGS } = CONFIG;
+const { BULK_SENDING_ENDPOINT } = CLIENT_SETTINGS;
+
+describe("lib/api/BulkSending: ", () => {
+  let mock: AxiosMockAdapter;
+  const bulkSendingAPI = new BulkSendingAPI(axios);
+
+  describe("class Testing(): ", () => {
+    describe("init: ", () => {
+      it("initalizes with all necessary params.", () => {
+        expect(bulkSendingAPI).toHaveProperty("send");
+      });
+    });
+
+    beforeAll(() => {
+      /**
+       * Init Axios interceptors for handling response.data, errors.
+       */
+      axios.interceptors.response.use(
+        (response) => response.data,
+        handleSendingError
+      );
+      mock = new AxiosMockAdapter(axios);
+    });
+
+    afterEach(() => {
+      mock.reset();
+    });
+
+    describe("send(): ", () => {
+      it("successfully sends email.", async () => {
+        const endpoint = `${BULK_SENDING_ENDPOINT}/api/send`;
+        const expectedResponseData = {
+          success: true,
+          message_ids: ["0c7fd939-02cf-11ed-88c2-0a58a9feac02"],
+        };
+        mock.onPost(endpoint).reply(200, expectedResponseData);
+
+        const emailData = {
+          from: {
+            email: "sender.mock@email.com",
+            name: "sender",
+          },
+          to: [
+            {
+              email: "recipient.mock@email.com",
+              name: "recipient",
+            },
+          ],
+          subject: "mock-subject",
+          text: "Mock text",
+          html: "<div>Mock text</div>",
+        };
+
+        const result = await bulkSendingAPI.send(emailData);
+
+        expect(mock.history.post[0].url).toEqual(endpoint);
+        expect(mock.history.post[0].data).toEqual(JSON.stringify(emailData));
+        expect(result).toEqual(expectedResponseData);
+      });
+
+      it("rejects with api error.", async () => {
+        const responseData = {
+          success: false,
+          errors: ["mock-error-1", "mock-error-2"],
+        };
+
+        const endpoint = `${BULK_SENDING_ENDPOINT}/api/send`;
+
+        mock.onPost(endpoint).reply(400, responseData);
+
+        const emailData = {
+          from: {
+            email: "sender.mock@email.com",
+            name: "sender",
+          },
+          to: [
+            {
+              email: "recipient.mock@email.com",
+              name: "recipient",
+            },
+          ],
+          subject: "mock-subject",
+          text: "Mock text",
+          html: "<div>Mock text</div>",
+        };
+
+        const expectedErrorMessage = responseData.errors.join(",");
+
+        expect.assertions(3);
+
+        try {
+          await bulkSendingAPI.send(emailData);
+        } catch (error) {
+          expect(mock.history.post[0].url).toEqual(endpoint);
+          expect(mock.history.post[0].data).toEqual(JSON.stringify(emailData));
+
+          if (error instanceof Error) {
+            expect(error.message).toEqual(expectedErrorMessage);
+          }
+        }
+      });
+
+      it("rejects with axios error.", async () => {
+        const emailData = {
+          from: {
+            email: "sender.mock@email.com",
+            name: "sender",
+          },
+          to: [
+            {
+              email: "recipient.mock@email.com",
+              name: "recipient",
+            },
+          ],
+          subject: "mock-subject",
+          text: "Mock text",
+          html: "<div>Mock text</div>",
+        };
+
+        const expectedErrorMessage = "Request failed with status code 404";
+
+        expect.assertions(2);
+
+        try {
+          await bulkSendingAPI.send(emailData);
+        } catch (error) {
+          expect(error).toBeInstanceOf(MailtrapError);
+
+          if (error instanceof MailtrapError) {
+            expect(error.message).toEqual(expectedErrorMessage);
+          }
+        }
+      });
+    });
+  });
+});