diff --git a/__tests__/lhisp-oauth-client.test.ts b/__tests__/lhisp-oauth-client.test.ts
new file mode 100644
index 0000000..d0fbf7d
--- /dev/null
+++ b/__tests__/lhisp-oauth-client.test.ts
@@ -0,0 +1,80 @@
+import axios from 'axios';
+import LhispOauthClient from "../src/lhisp-oauth-client";
+import { LhispOauthClientConstructorParams } from '../src/lhisp-oauth-client.t';
+
+// Mock jest and set the type
+jest.mock('axios');
+const mockedAxios = axios as jest.Mocked<typeof axios>;
+
+const apiUrl = "https://myapi.com";
+const authUrl = "https://auth.myapi.com/oauth/token";
+const clientId = "testClientdId";
+const clientSecret = "testClientSecret";
+const baseClientParams = { apiUrl, authUrl, clientId, clientSecret };
+const basicAuth = `Basic ${Buffer.from(`${clientId}:${clientSecret}`).toString('base64')}`;
+
+describe("lhisp-oauth-client", ()=>{
+    it("Shout Get Access Token with Standard Config", async ()=>{
+        const cli = getOauthClient();
+        mockedAxios.request.mockReset();
+        mockedAxios.request.mockResolvedValueOnce({
+            data: mockedAccessToken
+        });
+
+        const now = Date.now();
+        const accessToken = await cli.getAccessToken();
+        expect(accessToken).toBeDefined();
+        expect(accessToken.token_type).toBe(mockedAccessToken.token_type);
+        expect(accessToken.access_token).toBe(mockedAccessToken.access_token);
+        expect(accessToken.expires_in).toBe(mockedAccessToken.expires_in);
+        expect(accessToken.scope).toBe(mockedAccessToken.scope);
+        expect(accessToken.created_at).toBeGreaterThanOrEqual(now);
+        expect(mockedAxios.request).toBeCalledWith(expect.objectContaining({
+            url: authUrl,
+            method: "POST",
+            headers: {
+                Authorization: basicAuth,
+                'Content-Type': "application/json",
+            }
+        }));
+    });
+
+    it("Shout Get Access Token with Custom Auth Header", async ()=>{
+        const cli = getOauthClient({
+            ...baseClientParams,
+            authHeaderName: "CustomAuthorizationHeader"
+        });
+        mockedAxios.request.mockReset();
+        mockedAxios.request.mockResolvedValueOnce({
+            data: mockedAccessToken
+        });
+
+        const now = Date.now();
+        const accessToken = await cli.getAccessToken();
+        expect(accessToken).toBeDefined();
+        expect(accessToken.token_type).toBe(mockedAccessToken.token_type);
+        expect(accessToken.access_token).toBe(mockedAccessToken.access_token);
+        expect(accessToken.expires_in).toBe(mockedAccessToken.expires_in);
+        expect(accessToken.scope).toBe(mockedAccessToken.scope);
+        expect(accessToken.created_at).toBeGreaterThanOrEqual(now);
+        expect(mockedAxios.request).toBeCalledWith(expect.objectContaining({
+            url: authUrl,
+            method: "POST",
+            headers: {
+                CustomAuthorizationHeader: basicAuth,
+                'Content-Type': "application/json",
+            }
+        }));
+    });
+});
+
+function getOauthClient(opt:LhispOauthClientConstructorParams=baseClientParams){
+    return new LhispOauthClient(opt);
+}
+
+const mockedAccessToken = {
+    token_type: "Bearer",
+    access_token: "SomeAccessToken",
+    expires_in: 600,
+    scope: "cobrancas.boletos-requisicao cobrancas.boletos-info",
+}
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