update api.js api client, and axios mock, and add api.js unit tests

__mocks__/axios.js

@@ -0,0 +1,21 @@
+const axios = require('axios');
+
+jest.genMockFromModule('axios');
+
+axios.create = jest.fn(() => axios);
+axios.get = jest.fn(() => axios);
+axios.post = jest.fn(() => axios);
+axios.create.mockReturnValue({
+  get: axios.get,
+  post: axios.post
+});
+axios.get.mockResolvedValue('get results');
+axios.post.mockResolvedValue('post results');
+
+axios.customClearMocks = () => {
+  axios.create.mockClear();
+  axios.get.mockClear();
+  axios.post.mockClear();
+};
+
+module.exports = axios;