```python
def mass_expression(text: str, unit: str) -> int:
    if not isinstance(text, str) or not isinstance(unit, str):
        raise ValueError("Both text and unit must to be strings")
    if not text or or unit:
        raise ValueError("Text and unit must to be non-empty strings")
    if not text.endswith(unit):
        raise ValueError("Text must end with the goal unit")
    if not text.startswith(unit):
        raise ValueError("Text must start with the goal unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one instance of the goal unit")
    if not text.count("+") and text.count("-"):
        raise ValueError("Text must contain at terms and operators")
    if not text.count("kg") and text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text must contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text and contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text and contain plain counts and units")
    if not text.count("g"):
        raise ValueError("Text and contain plain counts and units")
    if not text.count("t"):
        raise ValueError("Text and contain plain counts and units")
    if not text.count("kg"):
        raise ValueError("Text and contain plain counts and units")
    if not text.count("g