React 测试库：测试属性/prop

我正在使用 TypeScript 编写一个 React 应用程序。我使用material-ui作为我的组件，使用react-testing-library作为我的单元测试。

我正在为 Material-ui 的 Grid 组件编写一个包装器，以便我始终拥有一个项目。

import Grid from "@material-ui/core/Grid";
import withStyles, { WithStyles } from "@material-ui/core/styles/withStyles";
import React, { PureComponent } from "react";
import styles from "./styles";

export interface OwnProps {
  className?: string;
}

export interface Props extends WithStyles<typeof styles>, OwnProps {}

export interface DefaultProps {
  className: string;
}

export class GridItem extends PureComponent<Props & DefaultProps> {
  static defaultProps: DefaultProps = {
    className: ""
  };

  render() {
    const { classes, children, className, ...rest } = this.props;
    return (
      <Grid
        data-testid="grid-item"
        item={true}
        {...rest}
        className={classes.grid + " " + className}
      >
        {children}
      </Grid>
    );
  }
}

export default withStyles(styles)(GridItem);

我想编写一个单元测试来检查是否item={true}。我尝试使用辅助库 jest-dom'stoHaveAttribute像这样：

import "jest-dom/extend-expect";
import React from "react";
import { cleanup, render } from "react-testing-library";
import GridItem, { OwnProps } from "./GridItem";
afterEach(cleanup);

const createTestProps = (props?: object): OwnProps => ({
  ...props
});

describe("Parallax", () => {
  const props = createTestProps();
  const { getByTestId } = render(<GridItem {...props} />);
  describe("rendering", () => {
    test("it renders the image", () => {
      expect(getByTestId("grid-item")).toHaveAttribute("item", "true");
    });
  });
});

但这个测试失败了：

● GridItem › rendering › it renders the image

    expect(element).toHaveAttribute("item", "true") // element.getAttribute("item") === "true"

    Expected the element to have attribute:
      item="true"
    Received:
      null

      14 |   describe("rendering", () => {
      15 |     test("it renders the image", () => {
    > 16 |       expect(getByTestId("grid-item")).toHaveAttribute("item", "true");
         |                                        ^
      17 |     });
      18 |   });
      19 | });

      at Object.toHaveAttribute (src/components/Grid/GridItem/GridItem.test.tsx:16:40)

Test Suites: 1 failed, 3 passed, 4 total
Tests:       1 failed, 3 passed, 4 total
Snapshots:   0 total
Time:        1.762s, estimated 2s
Ran all test suites related to changed files.

如何测试一个元素是否具有某个属性？

jest-dom toHaveAttribute断言断言item 属性当测试尝试测试时item prop.

itemprop 不一定会导致item属性，并且由于它是非标准属性，因此很可能不会。

react-testing-library传播功能测试并断言生成的 DOM，这需要了解组件如何工作。可以看出here https://github.com/mui-org/material-ui/blob/v3.3.2/packages/material-ui/src/Grid/Grid.js#L220, itemprops 会导致向网格元素添加一个类。

除了测试单元之外的所有单元都应该在单元测试中进行模拟，例如：

...
import GridItem, { OwnProps } from "./GridItem";

jest.mock("@material-ui/core/Grid", () => ({
  default: props => <div data-testid="grid-item" className={props.item && item}/>
}));

那么它可以被断言为：

  expect(getByTestId("grid-item")).toHaveClass("item");