from typing import Dict


def get_frequency_map(text: str, substring_length: int) -> Dict[str, int]:
    """
    Find the frequency of all substring of length in a given text
    >>> get_frequency_map("GTACGTACC", 1)
    {'G': 2, 'T': 2, 'A': 2, 'C': 3}
    >>> get_frequency_map("GTACGTACC", 2)
    {'GT': 2, 'TA': 2, 'AC': 2, 'CG': 1, 'CC': 1}
    >>> get_frequency_map("GTACGTACC", 4)
    {'GTAC': 2, 'TACG': 1, 'ACGT': 1, 'CGTA': 1, 'TACC': 1}
    >>> get_frequency_map("GTACGTACC", 6)
    {'GTACGT': 1, 'TACGTA': 1, 'ACGTAC': 1, 'CGTACC': 1}
    """
    assert substring_length > 0
    assert len(text) > 0

    freq_map = {}
    for index in range(len(text) - substring_length + 1):
        substr = text[index : index + substring_length]
        if substr in freq_map:
            freq_map[substr] += 1
        else:
            freq_map[substr] = 1
    return freq_map