def update_hmm(emission_matrix, unique_words, sentence):
    """
    Reads in hmm's emission matrix, unique_words, and the entire string of testdata.
    Returns nothing. Instead, alters the values of emission matrix by adding 0.00001 and normalizing.
    """
    EPSILON = 0.00001
    seen = False

    # check if we have seen a word already
    for word in sentence:
        if word not in unique_words:
            seen = True
            unique_words.add(word)
            for tag in emission_matrix:
                emission_matrix[tag][word] = 0

    # if we have any word that we have not seen already, do this
    if seen:
        # add 0.0001 to every tag / word in emission_matrix
        for tag in emission_matrix:
            for word in emission_matrix[tag]:
                emission_matrix[tag][word] += EPSILON

            # normalize
            row_sum = 0
            for word in emission_matrix[tag]:
                row_sum += emission_matrix[tag][word]
            for word in emission_matrix[tag]:
                emission_matrix[tag][word] /= row_sum