Function assert_not_modified::assert_not_modified

pub fn assert_not_modified<F, Data, Any>(data: &mut Data, test: F) where
    F: FnOnce(&mut Data) -> Any,
    Data: Clone + Eq + Debug, 

Helper function which panics if the given closure mutates the input data.

Panics

Panics if data is modified with message "Data was modified where it should not have been".

Example

use assert_not_modified::assert_not_modified;

// This bugged function wil return Err but still modify the data.
fn misleading_err(x: &mut i32) -> Result<(), String> {
    *x = *x + 1;
    // Throws an error but x is modified anyway. This is misleading.
    Err("Something wrong happened !".to_owned())
}

// This test will expose the lying function :
assert!(std::panic::catch_unwind(|| {
    let mut x = 3;
    assert_not_modified(&mut x, |x| misleading_err(x)); // Panics
})
.is_err());