Run additional tests by using a feature flag to "cargo test" - testing

Question

I have some tests that I would like to ignore when using cargo test and only run when explicitly passed a feature flag. I know this can be done by using #[ignore] and cargo test -- --ignored, but I'd like to have multiple sets of ignored tests for other reasons.
I have tried this:
#[test]
#[cfg_attr(not(feature = "online_tests"), ignore)]
fn get_github_sample() {}
This is ignored when I run cargo test as desired, but I can't get it to run.
I have tried multiple ways of running Cargo but the tests continue to be ignored:
cargo test --features "online_tests"
cargo test --all-features
I then added the feature definition into my Cargo.toml as per this page, but they continue to be ignored.
I am using workspaces in Cargo. I tried adding the feature definition in both Cargo.toml files with no difference.

Answer 1

Without a workspace
Cargo.toml
[package]
name = "feature-tests"
version = "0.1.0"
authors = ["An Devloper <an.devloper#example.com>"]
[features]
network = []
filesystem = []
[dependencies]
src/lib.rs
#[test]
#[cfg_attr(not(feature = "network"), ignore)]
fn network() {
panic!("Touched the network");
}
#[test]
#[cfg_attr(not(feature = "filesystem"), ignore)]
fn filesystem() {
panic!("Touched the filesystem");
}
Output
$ cargo test
running 2 tests
test filesystem ... ignored
test network ... ignored
$ cargo test --features network
running 2 tests
test filesystem ... ignored
test network ... FAILED
$ cargo test --features filesystem
running 2 tests
test network ... ignored
test filesystem ... FAILED
(some output removed to better show effects)
With a workspace
Layout
.
├── Cargo.toml
├── feature-tests
│   ├── Cargo.toml
│   ├── src
│   │   └── lib.rs
├── src
│   └── lib.rs
feature-tests contains the files from the first section above.
Cargo.toml
[package]
name = "workspace"
version = "0.1.0"
authors = ["An Devloper <an.devloper#example.com>"]
[features]
filesystem = ["feature-tests/filesystem"]
network = ["feature-tests/network"]
[workspace]
[dependencies]
feature-tests = { path = "feature-tests" }
Output
$ cargo test --all
running 2 tests
test filesystem ... ignored
test network ... ignored
$ cargo test --all --features=network
running 2 tests
test filesystem ... ignored
test network ... FAILED
(some output removed to better show effects)
With a virtual workspace
Virtual workspaces do not support specifying features (Cargo issue #4942). You will need to run the tests from within the sub project or specify the path to the appropriate Cargo.toml
Layout
.
├── Cargo.toml
└── feature-tests
├── Cargo.toml
└── src
└── lib.rs
feature-tests contains the files from the first section above.
Cargo.toml
[workspace]
members = ["feature-tests"]
Output
$ cargo test --all --manifest-path feature-tests/Cargo.toml --features=network
running 2 tests
test filesystem ... ignored
test network ... FAILED
$ cargo test --all --manifest-path feature-tests/Cargo.toml
running 2 tests
test filesystem ... ignored
test network ... ignored
(some output removed to better show effects)