I am trying to test an input tag but I want to test the content of the uploaded file. here is the code -

<input
  data-testid="file-input"
  type="file"
  accept=".csv, .tsv"
  onChange={(event) => {
    if (event.target.files !== null) {
      setCsvFile(event.target.files[0]);
      let reader = new FileReader();
      var content: string | ArrayBuffer | null | undefined;

      reader.onload = function () {
        content = reader.result;
        console.log(reader.result);
      };

      reader.onerror = function () {
        console.log(reader.error);
      };

      reader.readAsText(event.target.files[0]);
    }
  }}
/>;

How can I unit test what is being read by FileReader on file upload?