Tips for effectively testing an upload file feature using jest and vue-test-utils simulation

Currently, I am using jest along with vue-test-utils to test a method that uploads files. This particular method is located in the vue file component.

async uploadFiles(file){
  this.$refs.iconUpload.setAttribute('data-load', 'loading')
  let formData = new FormData();
  formData.append('image', file);

  try{
    const result = await fetch('/upload', {
      method: 'POST',
      body: formData,
    })
    const data = await result.json();
    if(data.status){
      this.$refs.iconUpload.setAttribute('data-load', 'success')
      this.$refs.btnClear.style.display = 'none';
      this.$refs.btnGoBack.style.display = 'none';
      this.uploadDone = true;
    }else {
      this.showSpecialError(this.$refs.elseError)
    }
  }catch (e){
    this.showSpecialError(this.$refs.elseError)
    return null
  }
}

In addition, I aim to perform tests on this method involving resolve and reject functionalities.

const file = {
  size: 500,
  type: 'image/png',
  name: 'image.png
};

const event = {
  target: {
    files: [file],
  },
};

global.fetch = jest.fn(() => Promise.resolve({
  json: () => Promise.resolve({ data })
}));

test('the function of sending the file returns the required response on a successful response', async () => {
    const result = await wrapper.vm.uploadFiles(event)
    expect(result).toEqual(file)
})

However, the current issue I am facing is that the test consistently returns null.

https://i.sstatic.net/L2gpp.png

Answer №1

When conducting the test, it appears that the uploadFiles function is expected to return a file, but in reality, it does not. To rectify this, consider adding the following line at the end of the try {} block:

return data;

Since uploadFiles is an asynchronous function, the returned value will automatically be encapsulated within a promise. This is equivalent to returning Promise.resolve(data) in a synchronous function.

However, it's important to note that simply returning data at the end of the try{} block may not be the ideal solution.

In your component method, you are currently checking for the existence of a truthy status property in the response from the /upload call using if (data.status). This approach is flawed as status codes such as 404 and 500 can also be considered truthy due to being finite positive numbers.

Considering the above issues, there are two options for addressing them:

a)
If you wish to proceed with testing the current component code, focus on verifying whether wrapper.vm.uploadDone is set to true when the fetch operation returns a response with a truthy status value. An example test case for this scenario is provided below:

// Test setup
global.fetch = jest.fn(() => Promise.resolve({
  json: () => Promise.resolve({ status: 404 })
}));

// Test case
test('uploadDone gets set to true when receiving a truthy response from /upload', async () => {
   expect(wrapper.vm.uploadDone).toBe(false);
   await wrapper.vm.uploadFiles({
     size: 500,
     type: 'image/png',
     name: 'image.png'
   });
   expect(wrapper.vm.uploadDone).toBe(true);
})

It should be noted that uploadFiles ideally should not update uploadDone when handling responses with statuses other than 200.

Alternatively,

b)
Seek assistance from a senior member of your team who can provide detailed explanations and guide the refactoring of the uploadFiles function. Testing should align with the intended behavior of the application, and if the current implementation deviates from expectations, writing tests may not be fruitful until the necessary changes are made.

Tests serve the purpose of ensuring consistent behavior under varying conditions, including failures in external systems. If your application is not meeting expectations, it's crucial to align the tests with the desired functionality and subsequently modify the code to meet those expectations.

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