def read_data(filename):
    """Read in patient data from ECG test data file

    An ECG, or electrocardiogram, records the electrical signals
    of the heart to diagnose a variety of heart problems, including
    arrythmias and previous heart attacks.  Raw ECG data must be
    filtered to remove background noise before it is analyzed by
    a cardiologist.  More info on ECGs can be found at:
    https://www.webmd.com/heart-disease/electrocardiogram-ekgs

    :param filename: string containing name of input test file

    :returns: string containing all ECG test data from input file
    """
    test = open(filename, 'r')
    test_data = test.read()
    test.close()
    # logging.info('Beginning analysis of new ECG trace using {}'.format(
    # filename.replace('test_data/', '')))
    return test_data