Fix "export everything" (#21434)

Fixes #21416 - this is identical to https://github.com/elastic/kibana/pull/21402, but adds testing to prevent a regression.

@chrisronline in the interest of speed, time, and stability for 6.4, I opted not to do a full functional test, but rather an API test to ensure that the API endpoint was interacting with the Saved Objects Client as expected.

src/core_plugins/kibana/server/routes/api/management/saved_objects/scroll.test.js

@@ -0,0 +1,86 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import Hapi from 'hapi';
+import { registerScrollForExportRoute } from './scroll';
+
+const createMockServer = () => {
+  const mockServer = new Hapi.Server({ debug: false });
+  mockServer.connection({ port: 8080 });
+  return mockServer;
+};
+
+describe(`POST /api/kibana/management/saved_objects/scroll/export`, () => {
+  test('requires "typesToInclude"', async () => {
+    const mockServer = createMockServer();
+    registerScrollForExportRoute(mockServer);
+
+    const headers = {};
+    const payload = {};
+
+    const request = {
+      method: 'POST',
+      url: `/api/kibana/management/saved_objects/scroll/export`,
+      headers,
+      payload
+    };
+
+    const { result, statusCode } = await mockServer.inject(request);
+    expect(statusCode).toEqual(400);
+    expect(result).toMatchObject({
+      message: `child "typesToInclude" fails because ["typesToInclude" is required]`
+    });
+  });
+
+  test(`uses "typesToInclude" when searching for objects to export`, async () => {
+    const mockServer = createMockServer();
+    const mockClient = {
+      find: jest.fn(() => {
+        return {
+          saved_objects: []
+        };
+      })
+    };
+
+    mockServer.decorate('request', 'getSavedObjectsClient', () => mockClient);
+
+    registerScrollForExportRoute(mockServer);
+
+    const headers = {};
+    const payload = {
+      typesToInclude: ['foo', 'bar']
+    };
+
+    const request = {
+      method: 'POST',
+      url: `/api/kibana/management/saved_objects/scroll/export`,
+      headers,
+      payload
+    };
+
+    const { result, statusCode } = await mockServer.inject(request);
+    expect(statusCode).toEqual(200);
+    expect(result).toEqual([]);
+
+    expect(mockClient.find).toHaveBeenCalledWith({
+      page: 1,
+      perPage: 1000,
+      type: ['foo', 'bar']
+    });
+  });
+});