Flaky tests when using minitest to check file creation

Can anyone point as to why my tests are being flaky (locally, and on circleCI) when testing a file creation / ActiveStorage?

In development, this code works fine, but I suspect theres some weird race condition or something in the tests.

I'm testing the below create_my_file method as a model test and controller test (various places), and it often fails when I check if the new file has been attached to my model.

As below, I use MyFileGenerator to create the file each time in our tmp folder, and we then use this file to attach and upload to S3. Then when we create another file, we first delete the tmp folder and recreate, to avoid files building up.

  def create_my_file
    if my_file.attached?
      my_file.purge
    end
    MyFileGenerator.new.create(my_file_data, id)
    my_file.attach(
      io: File.open(
        "#{Rails.root}/tmp/my_file/my_file_#{id}.docx"
      ),
      filename: "my_file_#{id}_#{Time.now.to_i}.docx",
      content_type: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'
    )
  end

MyFileGenerator.new.create

def create(data, meeting_id)
  doc = Docx::Document.open("#{Rails.root}/app/lib/docx/docx_templates/my_file).docx")

  populate_document(doc, data)

  # Save the new file
  make_tmp_directory
  doc.save("#{Rails.root}/tmp/my_file/my_file_#{meeting_id}.docx")
end

private

def make_tmp_directory
  # We need to store the file somewhere before uploading to S3
  dir = "#{Rails.root}/tmp/my_file/"
  # Clear existing files if exists, then make new dir
  FileUtils.remove_dir(dir, true) if File.exist?(dir)
  Dir.mkdir(dir)
end

Any suggestions to improve this, or pointers as to where the issue may be would be great.