Add regression tests to createApp entrypoint

Ensure that appropriate tasks are called depending on inquirer prompt answers,
and command-line argument options (--path, and --skip-install).

Signed-off-by: Colton Padden <colton.padden@fastmail.com>

packages/create-app/src/createApp.test.ts

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed 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 inquirer from 'inquirer';
+import { Command } from 'commander';
+import * as tasks from './lib/tasks';
+import createApp from './createApp';
+
+jest.mock('./lib/tasks');
+
+const promptMock = jest.spyOn(inquirer, 'prompt');
+const checkPathExistsMock = jest.spyOn(tasks, 'checkPathExistsTask');
+const templatingMock = jest.spyOn(tasks, 'templatingTask');
+const checkAppExistsMock = jest.spyOn(tasks, 'checkAppExistsTask');
+const createTemporaryAppFolderMock = jest.spyOn(
+  tasks,
+  'createTemporaryAppFolderTask',
+);
+const moveAppMock = jest.spyOn(tasks, 'moveAppTask');
+const buildAppMock = jest.spyOn(tasks, 'buildAppTask');
+
+describe('command entrypoint', () => {
+  beforeEach(() => {
+    promptMock.mockResolvedValueOnce({
+      name: 'MyApp',
+      dbType: 'PostgreSQL',
+    });
+  });
+
+  afterEach(() => {
+    jest.resetAllMocks();
+  });
+
+  test('should call expected tasks with no path option', async () => {
+    const cmd = {} as unknown as Command;
+    await createApp(cmd);
+    expect(checkAppExistsMock).toHaveBeenCalled();
+    expect(createTemporaryAppFolderMock).toHaveBeenCalled();
+    expect(templatingMock).toHaveBeenCalled();
+    expect(moveAppMock).toHaveBeenCalled();
+    expect(buildAppMock).toHaveBeenCalled();
+  });
+
+  it('should call expected tasks with path option', async () => {
+    const cmd = { path: 'myDirectory' } as unknown as Command;
+    await createApp(cmd);
+    expect(checkPathExistsMock).toHaveBeenCalled();
+    expect(templatingMock).toHaveBeenCalled();
+    expect(buildAppMock).toHaveBeenCalled();
+  });
+
+  it('should not call `buildAppTask` when `skipInstall` is supplied', async () => {
+    const cmd = { skipInstall: true } as unknown as Command;
+    await createApp(cmd);
+    expect(buildAppMock).not.toHaveBeenCalled();
+  });
+});