javascript - 无法在我的单元测试中使用 Jest 渲染 Vue 组件

Question

我正在尝试使用 Jest 在我的 Vue 单元测试中渲染一个组件，但我似乎无法让它工作。

日志显示:TypeError:无法读取 null 的属性“length”

我尝试过其他组件，效果很好。

ErrandsListTable.vue

<template>
  <div
    v-if="!error"
    class="flex-table flex-table--white-background flex-table--green-header flex-table--with-dropdown"
    :class="{ loading: loading }"
  >
    <div class="flex-table__row flex-table--header text--level-6">
      <div class="flex-table__cell flex-table__cell--width-3">
        {{ statusHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-3">
        {{ idHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-7">
        {{ descriptionHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-5">
        {{ typeHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-3">
        {{ dateOpenedHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-3">
        {{ dateClosedHeader }}
      </div>
      <div class="flex-table__cell flex-table__cell--width-1" />
    </div>

    <div
      v-for="(errand, index) in sliceArray(errands)"
      :key="!errand.id ? index : errand.id"
    >
      <div
        class="flex-table__row"
        :class="{ 'flex-table__row--closed': index !== selectedErrand }"
        @click="toggleExpanded(index)"
      >
        <div class="flex-table__cell flex-table__cell--width-3">
          {{ errand.status }}
        </div>
        <div class="flex-table__cell flex-table__cell--width-3">
          {{ errand.id }}
        </div>
        <div
          class="flex-table__cell flex-table__cell--width-7 flex-table__cell--show-on-mobile"
          :data-header="descriptionHeader"
        >
          {{ errand.description }}
        </div>
        <div class="flex-table__cell flex-table__cell--width-5">
          {{ errand.type }}
        </div>
        <div
          class="flex-table__cell flex-table__cell--width-3 flex-table__cell--show-on-mobile"
          :data-header="dateOpenedHeader"
        >
          {{ errand.orderDate }}
        </div>
        <div class="flex-table__cell flex-table__cell--width-3">
          {{ errand.deliveryDate }}
        </div>
        <div
          class="flex-table__cell flex-table__cell--width-1 flex-table__cell--dropdown-show-on-mobile"
        >
          <i
            class="icon-angle__small"
            :class="{ 'icon-angle__small--down': selectedErrand === index }"
          />
        </div>
      </div>

      <ErrandsListDetails
        v-if="selectedErrand >= 0 && selectedErrand === index"
        :errand="errand"
        v-bind="$props"
      />
    </div>

    <div
      v-if="errands.length >= numberOfErrandsLoaded"
      class="flex-table--load-more text--level-5"
    >
      <a href="#" @click="loadMore">
        {{ showMoreText }}
        <i class="icon-down" />
      </a>
    </div>
    <div
      v-if="errands.length < 1 && !loading"
      class="flex-table--error text--level-5"
    >
      {{ noCasesText }}
    </div>
    <div v-if="error && !loading" class="flex-table--error text--level-5">
      {{ errorText }}
    </div>
  </div>
</template>

<script>
import _ from "lodash";
import ErrandsListDetails from "./ErrandsListDetails.vue";

export default {
  components: {
    ErrandsListDetails: ErrandsListDetails
  },
  props: {
    componentTitle: {
      type: String,
      default: () => {
        return "";
      }
    },
    showMoreText: {
      type: String,
      default: "Visa fler ärenden"
    },
    statusHeader: {
      type: String,
      default: () => {
        return "Status";
      }
    },
    dateOpenedHeader: {
      type: String,
      default: () => {
        return "Beställt/Anmält";
      }
    },
    dateClosedHeader: {
      type: String,
      default: () => {
        return "Beräknad klar";
      }
    },
    idHeader: {
      type: String,
      default: () => {
        return "Ärendenummer";
      }
    },
    descriptionHeader: {
      type: String,
      default: () => {
        return "Beskrivning";
      }
    },
    typeHeader: {
      type: String,
      default: () => {
        return "Typ";
      }
    },
    fileDetails: {
      type: String,
      default: () => {
        return "Ladda ned beställningen som PDF:";
      }
    },
    commentsDetails: {
      type: String,
      default: () => {
        return "Noteringar";
      }
    },
    wordList: {
      type: String,
      default: () => {
        return "";
      }
    },
    attachment: {
      type: String,
      default: () => {
        return "";
      }
    },
    noCasesText: {
      type: String,
      default: () => {
        return "Det finns inget att visa";
      }
    },
    errorText: {
      type: String,
      default: () => {
        return "Något gick fel";
      }
    },
    createdOnFallback: {
      type: String,
      default: () => {
        return "-";
      }
    },
    closedOnFallback: {
      type: String,
      default: () => {
        return "-";
      }
    },
    errandsCounter: {
      type: Object,
      default: () => {
        return null;
      }
    },
    errands: {
      type: Array,
      default: () => {
        return null;
      }
    },
    loading: {
      type: Boolean,
      default: () => {
        return false;
      }
    }
  },
  data() {
    return {
      selectedErrand: -1,
      error: undefined,
      numberOfErrandsLoaded: 10
    };
  },
  methods: {
    toggleExpanded: function(index) {
      this.selectedErrand = this.selectedErrand === index ? -1 : index;
    },

    loadMore: function(event) {
      event.preventDefault();
      this.numberOfErrandsLoaded += 10;
    },

    sliceArray: function(array) {
      let val = _.orderBy(array, "orderDate", "desc");
      return val.slice(0, this.numberOfErrandsLoaded);
    }
  }
};
</script>

还要忽略这个组件尚未完成并且可能不一定涉及单元测试最相关的用例这一事实。我只是想知道为什么这个特定组件无法在我的测试中作为 Vue 实例加载？

import { shallowMount } from "@vue/test-utils";
import ErrandsListTable from "../ErrandsListTable.vue";

let wrapper;

describe("Errandslist table", () => {
  beforeEach(() => {
    wrapper = shallowMount(ErrandsListTable);
  });

  afterEach(() => {
    wrapper.destroy();
  });
  it("is a Vue instance", () => {
    expect(wrapper.isVueInstance).toBeTruthy();
  });
});

有人遇到同样的问题吗？如果是这样，有人可以向我解释一下你是如何解决的吗？

Answer 1

在您的模板中，您的errands 数组为空，因此您无法访问 length 属性。您要么必须在组件中处理这种情况，要么必须将此属性传递给组件。

设置默认值

errands: {
  type: Array,
  default: () => {
    return [];
  }
}

测试期间传递默认值

const wrapper = shallowMount(ErrandsListTable, {
  propsData: {
    errands: []
  }
})
expect(wrapper.props().errands.length).toBe(0)