Create a mock FileList to test file upload components.

FlieList-mock-creator.ts

/** list of mock File elements to pass the input[file] */
export function getBrowsedFiles(): FileList {
    return fileListFromArray([
        mockFileCreator({ name: 'file-one.png', type: 'image/png', size: 234 * 1000 }),
        mockFileCreator({ name: 'file-two.gif', type: 'image/gif', size: 56 * 1000 }),
    ]);
}

export function mockFileCreator({
    name = 'file.txt',
    size = 1024,
    type = 'plain/txt',
    lastModified = new Date(),
}) {
    const blob = new Blob(['a'.repeat(size)], { type });

    blob['lastModifiedDate'] = lastModified;

    return new File([blob], name, { type });
}

function fileListFromArray(files: File[]): FileList {
    const flMock = files.reduce(
        (accumulator, curr, i) => {
            accumulator[i] = curr;
            return accumulator;
        },
        { length: files.length },
    ) as any;

    flMock.item = function(index: number) {
        return this[index];
    }.bind(flMock);

    return flMock as FileList;
}