Is there a way to mock regular functions in rust?
Consider the following code:
fn main() {
println!("{}", foo());
}
fn get_user_input() -> u8 {
// Placeholder for some unknown value
42
}
fn foo() -> u8 {
get_user_input()
}
#[cfg(test)]
mod tests {
#[test]
fn test_foo() {
use super::*;
get_user_input = || 12u8;
assert_eq!(foo(), 12u8);
}
}
I would like to unit test foo()
without having to rely on the output of get_user_input()
.
I obviously cannot overwrite get_user_input()
like I tried in the example code.
I have only found ways to mock structs, traits and modules but nothing about mocking regular free functions. Am I missing something?
Edit: I have looked primarily at the mockall
crate.
CodePudding user response:
You could use cfg:
#[cfg(not(test))]
fn get_user_input() -> u8 {
// Placeholder for some unknown value
42
}
#[cfg(test)]
fn get_user_input() -> u8 {
12
}
Or dependency injection:
pub fn main() {
println!("{}", foo(get_user_input));
}
fn get_user_input() -> u8 {
// Placeholder for some unknown value
42
}
fn foo(get_user_input_: impl Fn() -> u8) -> u8 {
get_user_input_()
}
#[cfg(test)]
mod tests {
#[test]
fn test_foo() {
use super::*;
let get_user_input = || 12u8;
assert_eq!(foo(get_user_input), 12u8);
}
}