Jasmine unit test for file size with TypeScript in Angular

Searching for best practice how to test File size on input type="file" change event.

Right now my test spec looks like this:

it('attach file with too large size', () => {
const file: File = {
name: 'filename',
type: 'image/png',
size: 8242880,
lastModified: 1,
lastModifiedDate: new Date(),
webkitRelativePath: '',
msClose: () => {},
msDetachStream: () => {},
slice: (): Blob => null,
};
const event = { target: { files: [file] } };

component.onFileChange(event); // file validation happens into it too

const error = control.getError('file_size');
expect(error).toBeTruthy();
});


Is there better way how to set File size property with TypeScript? When I am trying to setting size property directly to File object, it's not allowed because size property is read-only.

const file = new File([''], 'filename', { type: 'image/png' });
file.size = 8242880; // TS error


Current way how I am mocking File object where I need to define all File object properties for me isn't looking very beautiful, but can't find any better way. Any ideas?

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