The assert_fn library supplies a proc macro which can be used to turn test helper functions into assert! style macros. It is designed to be used where your test helper is performing an assert for you, for example:
```rust fn checkeqifdoubled(a: usize, b: usize) { asserteq!(a * 2, b) }
checkeqifdoubled(1, 2); checkeqifdoubled(2, 4); checkeqif_doubled(4, 8); ```
There are two reasons you'd want to do this:
assert! style macros are easy to spot in a test. They help others reading your test understand that this is where you are asserting correctness.check_eq_if_doubled the panic would originate on line 2, rather than the line which triggered the failure. In more complex tests this can make it hard to track down where the test is broken.Using assert_fn the above can be written as:
```rust use assertfn::assertfn;
fn eqifdoubled(a: usize, b: usize) -> bool { a * 2 == b }
asserteqifdoubled!(1, 2); asserteqifdoubled!(2, 4); asserteqif_doubled!(4, 8); ```
Or if you want to use assert_eq! instead of assert! so you can see what the values were, just return a tuple instead of a bool:
```rust use assertfn::assertfn;
fn eqifdoubled(a: usize, b: usize) -> (usize, usize) { (a * 2, b) }
asserteqifdoubled!(1, 2); asserteqifdoubled!(2, 4); asserteqif_doubled!(4, 8); ```
In both of these examples the failure will be logged against the line in your test on which the error originated instead of inside a line inside the eq_if_doubled.
See the Rust docs for lots more examples.
Because macros have to be defined before they can be used, your helper functions must be declared above the tests you want to use them in.
If you get a cannot find macro error check that your functions are in the correct order.