T7-ActionTests.md

Testing Lab 7: Action Tests

Objectives

• Mock the API
• Mock the Store
• Test Success and Failure

Steps

Mock the API

1. Create the directory src\projects\__mocks__.

   __mocks__ begins and ends with two underscores and is case-sensitive

2. Create the file src\projects\__mocks__\projectAPI.js to mock the projectAPI.

3. Mock the get method.

   src\projects\__mocks__\projectAPI.js

   import { MOCK_PROJECTS } from '../MockProjects';
   const projectAPI = {
     get(page = 1, limit = 20) {
       return Promise.resolve(MOCK_PROJECTS);
     },
   };
   
   export { projectAPI };

Mock the Store

1. Open a command prompt (Windows) or terminal (Mac).

2. Change the current directory to working\keeptrack.

3. Run one of the following sets of commands:

   npm

    npm install redux-mock-store @types/redux-mock-store --save-dev

   Yarn

   yarn add redux-mock-store @types/redux-mock-store --save-dev

4. Create the directory src\projects\state\__tests__.

   __tests__ begins and ends with two underscores and is case-sensitive

5. Create the file src\projects\state\__tests__\projectActions-test.js

6. Add the test setup code including mocking the store away.

   src\projects\state\__tests__\projectActions-test.js

   import configureMockStore from 'redux-mock-store';
   import ReduxThunk from 'redux-thunk';
   import { initialAppState } from '../../../state';
   import { loadProjects } from '../projectActions';
   import {
     LOAD_PROJECTS_REQUEST,
     LOAD_PROJECTS_SUCCESS,
     LOAD_PROJECTS_FAILURE,
   } from '../projectTypes';
   import { projectAPI } from '../../projectAPI';
   import { MOCK_PROJECTS } from '../../MockProjects';
   jest.mock('../../projectAPI');
   
   const middlewares = [ReduxThunk];
   const mockStoreCreator = configureMockStore(middlewares);
   
   describe('Project Actions', () => {
     let store;
   
     beforeEach(() => {
       store = mockStoreCreator(initialAppState);
     });
   });

Note that the jest.mock replaces the actual implementation of the projectAPI with the mock we created in the last step. This is done by convention in Jest which replaces the implementation with the exported function or object in the __mocks__ directory.

1. At this point, you will receive the following error:

   FAIL  src/projects/state/__tests__/projectActions-test.js
   ● Test suite failed to run
   
    Your test suite must contain at least one test.

Test Success and Failure

1. Test that an error is returned when loading projects fails.

   src/projects/state/__tests__/projectActions-test.js

   import configureMockStore from 'redux-mock-store';
   import ReduxThunk from 'redux-thunk';
   import { initialAppState } from '../../../state';
   import { loadProjects } from '../projectActions';
   import {
     LOAD_PROJECTS_REQUEST,
     LOAD_PROJECTS_SUCCESS,
     LOAD_PROJECTS_FAILURE
   } from '../projectTypes';
   import { projectAPI } from '../../projectAPI';
   import { MOCK_PROJECTS } from '../../MockProjects';
   jest.mock('../../projectAPI');
   
   const middlewares = [ReduxThunk];
   const mockStoreCreator = configureMockStore(middlewares);
   
   describe('Project Actions', () => {
     let store: any;
   
     beforeEach(() => {
       store = mockStoreCreator(initialAppState);
     });
   
   +  test('should return error', () => {
   +    projectAPI.get = jest
   +      .fn(
   +        // leave this commented initially
   +        // projectAPI.get
   +      )
   +      .mockImplementationOnce(() => {
   +        return Promise.reject('failed');
   +      });
   +
   +    const expectedActions = [
   +      { type: LOAD_PROJECTS_REQUEST },
   +      {
   +        type: LOAD_PROJECTS_FAILURE,
   +        payload: 'failed'
   +      }
   +    ];
   +
   +    return store.dispatch(loadProjects(1)).then(() => {
   +      const actions = store.getActions();
   +      expect(actions).toEqual(expectedActions);
   +    });
   +  });
   
   });
   

2. The new test should pass.

    PASS  src/projects/state/__tests__/projectActions-test.js

3. Attempt to test that the projects load successfully by adding the code.

   src/projects/state/__tests__/projectActions-test.js

   import configureMockStore from 'redux-mock-store';
   import ReduxThunk from 'redux-thunk';
   import { initialAppState } from '../../../state';
   import { loadProjects } from '../projectActions';
   import {
     LOAD_PROJECTS_REQUEST,
     LOAD_PROJECTS_SUCCESS,
     LOAD_PROJECTS_FAILURE
   } from '../projectTypes';
   import { projectAPI } from '../../projectAPI';
   import { MOCK_PROJECTS } from '../../MockProjects';
   jest.mock('../../projectAPI');
   
   const middlewares = [ReduxThunk];
   const mockStoreCreator = configureMockStore(middlewares);
   
   describe('Project Actions', () => {
     let store;
   
     beforeEach(() => {
       store = mockStoreCreator(initialAppState);
     });
   
     test('should return error', () => {
       projectAPI.get = jest
         .fn(
           // leave this commented initially
           // projectAPI.get
         )
         .mockImplementationOnce(() => {
           return Promise.reject('failed');
         });
   
       const expectedActions = [
         { type: LOAD_PROJECTS_REQUEST },
         {
           type: LOAD_PROJECTS_FAILURE,
           payload: 'failed'
         }
       ];
   
       return store.dispatch(loadProjects(1)).then(() => {
         const actions = store.getActions();
         expect(actions).toEqual(expectedActions);
       });
     });
   
   +  test('should load projects successfully', () => {
   +    const expectedActions = [
   +      { type: LOAD_PROJECTS_REQUEST },
   +      {
   +        type: LOAD_PROJECTS_SUCCESS,
   +        payload: { projects: MOCK_PROJECTS, page: 1 }
   +      }
   +    ];
   +
   +    return store.dispatch(loadProjects(1)).then(() => {
   +      const actions = store.getActions();
   +      expect(actions).toEqual(expectedActions);
   +    });
   +  });
   });

4. The test fails with the error below because no default mock implementation is set for the get method to revert back to after calling mockImplementationOnce executes once for the error test case.

   TypeError: Cannot read property 'then' of undefined
   

5. Uncomment the line below to set the default mock implementation back to the method defined in src\projects\__mocks__\projectAPI.js.

   Be sure that projectAPI.get is inside the .fn() (.fn(projectAPI.get)).

   src/projects/state/__tests__/projectActions-test.js

   ...
   describe('Project Actions', () => {
     let store;
   
     beforeEach(() => {
       store = mockStoreCreator(initialAppState);
     });
   
     test('should return error', () => {
       projectAPI.get = jest
         .fn(
           // leave this commented initially
   -       // projectAPI.get
   +       projectAPI.get
         )
         .mockImplementationOnce(() => {
           return Promise.reject('failed');
         });
   
       const expectedActions = [
         { type: LOAD_PROJECTS_REQUEST },
         {
           type: LOAD_PROJECTS_FAILURE,
           payload: 'failed'
         }
       ];
   
       return store.dispatch(loadProjects(1)).then(() => {
         const actions = store.getActions();
         expect(actions).toEqual(expectedActions);
       });
     });
   
     test('should load projects successfully', () => {
       const expectedActions = [
         { type: LOAD_PROJECTS_REQUEST },
         {
           type: LOAD_PROJECTS_SUCCESS,
           payload: { projects: MOCK_PROJECTS, page: 1 }
         }
       ];
   
       return store.dispatch(loadProjects(1)).then(() => {
         const actions = store.getActions();
         expect(actions).toEqual(expectedActions);
       });
     });
   });

6. All tests including the 'should load projects successfully' should now pass.

   PASS  src/projects/state/__tests__/projectActions-test.js

---

✔ You have completed Lab 7