Testing Lab 3: More Component Testing

Objectives

• Test Setup
• Testing a Prop
• Testing a Function Prop
• Taking a Snapshot

Steps

Test Setup

1. Create the directory src\projects\__tests__.

2. Create the file src\projects\__tests__\ProjectCard-test.js.

3. Add the setup code below to test the component.

   src\projects\__tests__\ProjectCard-test.js

import { render, screen } from "@testing-library/react";
import React from "react";
import { Project } from "../Project";
import ProjectCard from "../ProjectCard";

describe("<ProjectCard />", () => {
  let project;
  let handleEdit;
  beforeEach(() => {
    project = new Project({
      id: 1,
      name: "Mission Impossible",
      description: "This is really difficult",
      budget: 100,
    });
    handleEdit = jest.fn();
  });

  it("should initially render", () => {
    render(<ProjectCard project={project} onEdit={handleEdit} />);
  });
});

1. Verify the test fails.

   useHref() may be used only in the context of a <Router> component.

2. Wrap the component in a MemoryRouter.

   import { render, screen } from '@testing-library/react';
   import React from 'react';
   + import { MemoryRouter } from 'react-router-dom';
   import { Project } from '../Project';
   import ProjectCard from '../ProjectCard';
   
   describe('<ProjectCard />', () => {
     let project;
     let handleEdit;
     beforeEach(() => {
       project = new Project({
         id: 1,
         name: 'Mission Impossible',
         description: 'This is really difficult',
         budget: 100,
       });
       handleEdit = jest.fn();
     });
   
     it('should initially render', () => {
       render(
   +      <MemoryRouter>
           <ProjectCard project={project} onEdit={handleEdit} />
   +      </MemoryRouter>
       );
     });
   });
   

<MemoryRouter> - is a <Router> that keeps the history of your "URL" in memory (does not read or write to the address bar). Useful in tests and non-browser environments like React Native.

1. Verify the initial test now passes.

   PASS  src/projects/__tests__/ProjectCard-test.js

Testing a Prop

1. Open a command-prompt or terminal and run the following command to install user-event from the core testing library behind React testing library.

   npm install --save-dev @testing-library/user-event @testing-library/dom

2. Test that the project property renders correctly.

   src\projects\__tests__\ProjectCard-test.js

...

describe('<ProjectCard />', () => {
  let project;
  let handleEdit;
  beforeEach(() => {
    project = new Project({
      id: 1,
      name: 'Mission Impossible',
      description: 'This is really difficult',
      budget: 100,
    });
    handleEdit = jest.fn();
  });

  it('should initially render', () => {
    render(
      <MemoryRouter>
        <ProjectCard project={project} onEdit={handleEdit} />
      </MemoryRouter>
    );
  });

+  it('renders project properly', () => {
+    render(
+      <MemoryRouter>
+        <ProjectCard project={project} onEdit={handleEdit} />
+      </MemoryRouter>
+    );
+    expect(screen.getByRole('heading')).toHaveTextContent(project.name);
+    // screen.debug(document);
+    screen.getByText(/this is really difficult\.\.\./i);
+    screen.getByText(/budget : 100/i);
+  });

});

1. Verify the test passes.

   PASS  src/projects/__tests__/ProjectCard-test.js
   ...
    ✓ renders project properly

Testing a Function Prop

1. Open a command-prompt or terminal and run the following commands to install a more recent version of the @testing-library/user-event package.

   npm uninstall @testing-library/user-event
   npm install @testing-library/user-event@14

2. Test that the handler prop is called when edit is clicked.

   src\projects\__tests__\ProjectCard-test.js

   import { render, screen } from '@testing-library/react';
   import React from 'react';
   import { MemoryRouter } from 'react-router-dom';
   import { Project } from '../Project';
   import ProjectCard from '../ProjectCard';
   + import userEvent from '@testing-library/user-event';
   
   describe('<ProjectCard />', () => {
     let project;
     let handleEdit;
     beforeEach(() => {
       project = new Project({
         id: 1,
         name: 'Mission Impossible',
         description: 'This is really difficult',
         budget: 100,
       });
       handleEdit = jest.fn();
     });
   
     it('should initially render', () => {
       render(
         <MemoryRouter>
           <ProjectCard project={project} onEdit={handleEdit} />
         </MemoryRouter>
       );
     });
   
     it('renders project properly', () => {
       render(
         <MemoryRouter>
           <ProjectCard project={project} onEdit={handleEdit} />
         </MemoryRouter>
       );
       expect(screen.getByRole('heading')).toHaveTextContent(project.name);
       // screen.debug(document);
       screen.getByText(/this is really difficult\.\.\./i);
       screen.getByText(/budget : 100/i);
     });
   
   +  it('handler called when edit clicked', async () => {
   +    render(
   +      <MemoryRouter>
   +        <ProjectCard project={project} onEdit={handleEdit} />
   +      </MemoryRouter>
   +    );
   +    // this query works screen.getByText(/edit/i)
   +    // but using role is better
   +    const user = userEvent.setup();
   +    await user.click(screen.getByRole('button', { name: /edit/i }));
   +    expect(handleEdit).toBeCalledTimes(1);
   +    expect(handleEdit).toBeCalledWith(project);
   +  });
   });
   

3. Verify the test passes.

   PASS  src/projects/__tests__/ProjectCard-test.js

4. Refactor the ProjectCard-test.js to use use a setup function to render the component at the start of each test.

   import { render, screen } from "@testing-library/react";
   import React from "react";
   import { MemoryRouter } from "react-router-dom";
   import { Project } from "../Project";
   import ProjectCard from "../ProjectCard";
   import userEvent from "@testing-library/user-event";
   import renderer from "react-test-renderer";
   
   describe("<ProjectCard />", () => {
     let project;
     let handleEdit;
   
     const setup = () =>
       render(
         <MemoryRouter>
           <ProjectCard project={project} onEdit={handleEdit} />
         </MemoryRouter>
       );
   
     beforeEach(() => {
       project = new Project({
         id: 1,
         name: "Mission Impossible",
         description: "This is really difficult",
         budget: 100,
       });
       handleEdit = jest.fn();
     });
   
     it("should initially render", () => {
       setup();
     });
   
     it("renders project properly", () => {
       setup();
       expect(screen.getByRole("heading")).toHaveTextContent(project.name);
       // screen.debug(document);
       screen.getByText(/this is really difficult\.\.\./i);
       screen.getByText(/budget : 100/i);
     });
   
     it("handler called when edit clicked", async () => {
       setup();
       // this query works screen.getByText(/edit/i)
       // but using role is better
       // eslint-disable-next-line testing-library/render-result-naming-convention
       const user = userEvent.setup();
       await user.click(screen.getByRole("button", { name: /edit/i }));
       expect(handleEdit).toBeCalledTimes(1);
       expect(handleEdit).toBeCalledWith(project);
     });
   
     test("snapshot", () => {
       const tree = renderer
         .create(
           <MemoryRouter>
             <ProjectCard project={project} onEdit={handleEdit} />
           </MemoryRouter>
         )
         .toJSON();
       expect(tree).toMatchSnapshot();
     });
   });

   Why not just put the setup code in the beforeEach? See this ESLint rule for react-testing-library.

Taking a Snapshot

1. Take a snapshot of the component.

   src\projects\__tests__\ProjectCard-test.js

   import { render, screen } from '@testing-library/react';
   import React from 'react';
   import { MemoryRouter } from 'react-router-dom';
   import { Project } from '../Project';
   import ProjectCard from '../ProjectCard';
   import userEvent from '@testing-library/user-event';
   + import renderer from 'react-test-renderer';
   
   describe('<ProjectCard />', () => {
     let project;
     let handleEdit;
     beforeEach(() => {
       ...
     });
   
   ...
   
   +  test('snapshot', () => {
   +    const tree = renderer
   +      .create(
   +        <MemoryRouter>
   +          <ProjectCard project={project} onEdit={handleEdit} />
   +        </MemoryRouter>
   +      )
   +      .toJSON();
   +    expect(tree).toMatchSnapshot();
   +  });
   });
   

2. Verify the snapshot is taken.

   ✓ 1 snapshot written

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✔ You have completed Testing Lab 3