netdog: Make net_config unit tests reusable across versions

[zmrow]

Issue number:
Related to #2204

Description of changes:
It's probably easiest to read this PR by commit, since the second commit has a decent amount of noise from moving the test_data files around.

As we add versions to net_config we need to be able to run the same set of unit tests across multiple versions. Net config versions are typically "additive", meaning that new versions add support for a new feature while continuing to support previous features. Rust's default test tooling doesn't allow parameterizing tests, and while one could loop over versions within a single test, the output of the cargo test tooling is less than satisfactory since you get a single line for a test.

The objectives:

• cargo test output must show a line for each network config version/test
• Easily run a set of tests across multiple versions; no copy/paste of test code between versions
• It must be easy to add new tests for upcoming versions.

This PR achieves the above objective by moving the actual test code into macros. Each macro contains a group of tests for a given feature. The macros are declarative and generate the appropriate test code, using the version as a key. Each macro's associated test data files are in a similarly named directory and templated, using the version.

Using the test macros in each net config version involves importing the macro inside the #[cfg(test)] block, and invoking it:

// This is an example for V1 net config
#[cfg(test)]
mod tests {
    use crate::net_config::test_macros::basic_tests;
    use crate::net_config::test_macros::dhcp_tests;

    // The macros take a version as their only parameter
    basic_tests!(1);
    dhcp_tests!(1);
...
}

The output includes a single line for each version and test. It would look like the following for a v1 and (not yet implemented) v2.

test net_config::v1::tests::dhcp::invalid_dhcp_config ... ok
test net_config::v1::tests::dhcp::invalid_dhcp6_options ... ok
test net_config::v1::tests::basic::multiple_primary_interfaces ... ok
test net_config::v1::tests::basic::undefined_primary_interface ... ok
test net_config::v2::tests::dhcp::invalid_dhcp_config ... ok
test net_config::v2::tests::dhcp::invalid_dhcp6_options ... ok
test net_config::v2::tests::basic::multiple_primary_interfaces ... ok
test net_config::v2::tests::basic::undefined_primary_interface ... ok

Commit messages:

    netdog: Add macros to simplify and improve net config testing
    
    This commit adds a new module `test_macros` inside of `net_config`.  The
    module is meant to contain a group of declarative macros, each of which
    contain a scoped group of tests and can be used across net config
    versions.  The macros themselves are declarative and define a new module
    that contains all the tests.  This allows us to use the same tests
    across all versions of net config, and get nicely formatted `cargo test`
    output showing the net config version, module, and test.  This is much
    nicer than looping over versions within a single test, and provides much
    better error output for the user

    netdog: Update net_config to use test macros
    
    This change updates `net_config` to take advantage of the previously
    added test macros.  It removes the majority of the tests from `mod.rs`,
    since the test themselves were moved to macros.  It updates the location
    of the test data files, and templates the version.  The last and final
    change is to add the test macros to `v1`.

Testing done:

• Ensure all the unit tests continue to pass

 $ cargo test
    Finished test [unoptimized + debuginfo] target(s) in 0.09s
     Running unittests src/main.rs (/home/fedora/bottlerocket/bottlerocket/sources/target/debug/deps/netdog-a2a46d1268055d1c)

running 24 tests
test cli::prepare_primary_interface::tests::default_sysctls ... ok
test net_config::tests::multiple_interface_from_cmdline ... ok
test interface_name::tests::valid_interface_name ... ok
test interface_name::tests::invalid_interface_name ... ok
test net_config::tests::no_interfaces_cmdline ... ok
test net_config::tests::no_interfaces_net_config ... ok
test net_config::tests::ok_cmdline ... ok
test net_config::v1::tests::basic::no_interfaces ... ok
test net_config::v1::tests::basic::invalid_interface_config ... ok
test net_config::v1::tests::dhcp::dhcp4_missing_enable ... ok
test net_config::v1::tests::dhcp::invalid_dhcp4_options ... ok
test net_config::v1::tests::invalid_interface_from_str ... ok
test net_config::v1::tests::dhcp::dhcp6_missing_enable ... ok
test net_config::v1::tests::basic::invalid_version ... ok
test net_config::v1::tests::ok_interface_from_str ... ok
test net_config::v1::tests::dhcp::invalid_dhcp_config ... ok
test net_config::v1::tests::dhcp::invalid_dhcp6_options ... ok
test net_config::v1::tests::basic::multiple_primary_interfaces ... ok
test net_config::v1::tests::basic::undefined_primary_interface ... ok
test net_config::tests::ok_net_config ... ok
test net_config::v1::tests::basic::defined_primary_interface ... ok
test net_config::v1::tests::basic::ok_config ... ok
test wicked::tests::interface_config_from_str ... ok
test wicked::tests::net_config_to_interface_config ... ok

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[etungsten]

🌮

[markusboehme]

The choice of macros here is an interesting one, but seems to fit the bill! Definitely passes my Rust newb readability check. 🥇

[zmrow]

^ Per @bcressey, moves to handlebars as the template renderer