Force tests to use a library's feature flag

help
1

And on the heels of my last post regarding feature flags, I have a follow-up.

Say I have:

[dependencies]
serde = { version = "1.0", optional = true }

[dev-dependencies]
serde_json = "1.0"

and have successfully defined serde trait implementations for my types, but guarded by #[cfg(feature = "serde")]. In a tests/serde.rs I've got:

#[test]
fn serde_instances() {
    assert!(serde_json::from_str::<Kanji>("合").is_ok());
}

but the compiler complains that the Deserialize instance is missing. I realize that I can call cargo test --features=serde and get it to work, but is it possible to force the test suite to always assume that feature flag?

Please and thanks.

2

It's not quite the same, but the closest thing is the required-features field in Cargo.toml:

[[test]]
name = "serde"
required-features = ["serde"]

Now Cargo will build and run that test only when serde is enabled. So if you run cargo test --features serde (or cargo test --all-features), it will run, but otherwise it will be ignored.

Unfortunately, I don't think there's a way for a plain cargo test to automatically enable non-default features.