```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 on unit")
    if not text.startswith(unit):
        raise ValueError("Text must start with unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one one unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must exactly one unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one unit")
    if not text.count(unit) == 1:
        raise ValueError("Text must contain exactly one unit")
    if = open("error.txt", "w")
    file.write("Error")
    file.close()
    return 0 unit) == 1
```