vue unit test get data of component - vue.js

Question

I am testing if a function works,
The function doesn't return anything but infact changes the data in the component
This is the test I am trying to write
describe('ModalAddCollectionCSV', () => {
it('Test load csv function', () => {
const localVue = createLocalVue()
const wrapper = shallowMount(AddCSV, {
localVue,
propsData: {
visible: true,
},
})
var fileDict = [{ file: new Blob([wrongDateFormat]) }]
wrapper.vm.loadcsv(fileDict)
expect(wrapper.html()).toContain('error')
})
})
I am expecting some changes to the data of the component
data() {
return {
collections: [],
inlineVisibility: false,
inlineTitle: '',
inlineSubtitle: '',
inlineKind: 'info',
loading: false,
}
},
This is the function I am testing in unit test, as you see it doesn't return anything just changes the data at the end of it
async loadcsv(element) {
const reader = new FileReader()
const file = element[0].file
this.toggleLoading()
reader.onload = async (e) => {
try {
//Normalising headers
const results = e.target.result
let resultSplit = results.split('\n')
const header = resultSplit[0]
.toLowerCase()
.replace(/[^a-zA-Z,]/g, '')
.trim()
resultSplit[0] = header
let table = resultSplit.join('\n')
const rows = await d3.csvParse(table)
await Promise.all(
rows.map(async (row) => {
if (!(this.getSerial(row).length == 9)) {
if (!this.getName(row)) {
throw `Please enter Person of interest`
}
if (!row.country) {
throw `Country for ${this.getName(
row,
)} is empty`
}
}
)
this.inlineVisibility = false
this.$emit('rowEmit', {
collections: this.row,
})
this.toggleLoading()
this.collections = []
this.$refs.modal.hide()
} catch (err) {
this.collections = []
this.inlineNotification('error', 'Unable to process CSV', `${err}.`)
}
}
reader.readAsText(file)
},
Is there a way to check emit action or error action?
I tried wrapper.text()
Wrapper.html()
but no difference