Add test for create data source picker handler

Signed-off-by: Huy Nguyen <73027756+huyaboo@users.noreply.github.com>

src/plugins/vis_type_timeseries/public/application/components/lib/create_data_source_change_handler.test.ts

@@ -0,0 +1,49 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { createDataSourcePickerHandler } from './create_data_source_change_handler';
+
+describe('createDataSourcePickerHandler()', () => {
+  let handleChange: jest.Mock<any, any>;
+  let changeHandler: (selectedOptions: []) => void;
+
+  beforeEach(() => {
+    handleChange = jest.fn();
+    changeHandler = createDataSourcePickerHandler(handleChange);
+  });
+
+  test.each([
+    {
+      id: undefined,
+    },
+    {},
+  ])(
+    'calls handleChange() and sets data_source_id to undefined if id cannot be found or is undefined',
+    ({ id }) => {
+      // @ts-ignore
+      changeHandler([{ id }]);
+      expect(handleChange.mock.calls.length).toEqual(1);
+      expect(handleChange.mock.calls[0][0]).toEqual({
+        data_source_id: undefined,
+      });
+    }
+  );
+
+  test.each([
+    {
+      id: '',
+    },
+    {
+      id: 'foo',
+    },
+  ])('calls handleChange() function with partial and updates the data_source_id', ({ id }) => {
+    // @ts-ignore
+    changeHandler([{ id }]);
+    expect(handleChange.mock.calls.length).toEqual(1);
+    expect(handleChange.mock.calls[0][0]).toEqual({
+      data_source_id: id,
+    });
+  });
+});