Testing and conformance

How dxn_i18n is tested - the Unicode MessageFormat Working Group's conformance suite, the feature test groups and CI - and how to test your own messages, plural forms and custom functions.

The library’s behavior is pinned by the Unicode MessageFormat Working Group’s conformance suite plus a test file per feature. Your own messages deserve tests too: a plural form missing for one language is invisible until a user hits it.

#The conformance suite

crates/dxn_i18n/tests/conformance/ holds the Working Group’s JSON test files, copied unchanged from unicode-org/message-format-wg (test/tests/) at commit 16372a6a02f41728be472a5921ba7c91774edeac, under the Unicode License. tests/conformance.rs runs every file: 17 files with 462 test cases in this copy. It checks the formatted text and the types of the errors (unresolved-variable, bad-operand, syntax-error and so on), for syntax, the data model, pattern selection, fallbacks, bidi isolation, the u: options and each default function.

The suite’s own test functions (:test:function, :test:select, :test:format) are implemented in the runner as a custom FunctionRegistry, following the suite’s README. The runner skips no case. All pass, and a case that fails fails the whole the_working_groups_suite_passes test with a list of every failure. To update, copy newer files over the directory, change the commit in tests/conformance/README.md and run cargo test -p dxn_i18n --test conformance.

#Feature tests and CI

Tests are grouped by feature, one file in crates/dxn_i18n/tests/ each:

The README’s and rustdoc’s examples run as 5 doc tests. Run one group with cargo test -p dxn_i18n --test selection. CI (.github/workflows/ci.yml) runs on Linux, macOS and Windows: cargo fmt --check, a check that no UI framework is in the dependency tree, cargo clippy --all-targets --all-features -- -D warnings, cargo test --workspace --all-features, cargo check for wasm32-unknown-unknown, and cargo package --workspace --list. Separate jobs build the rustdoc with missing-docs as an error and check the minimum Rust version, 1.97.

#Test your own messages

The pattern in the library’s tests: format with a known locale and assert that no errors came out, so a bad option or a missing argument fails the test instead of passing with a fallback in the text.

use dxn_i18n::{Args, Message, MessageFormatter};
use dxn_intl::parse_locale;

fn render(tag: &str, source: &str, args: Args) -> String {
    let message = Message::parse(source).expect("the message parses");
    let formatted = MessageFormatter::new(parse_locale(tag).expect("a language tag")).format(&message, &args);
    assert!(formatted.errors.is_empty(), "{source}: {:?}", formatted.errors);
    formatted.text
}

assert_eq!(render("en", "Hi {$name}", Args::new().with("name", "Ana")), "Hi Ana");

Put calls like this in #[test] functions. For bundles, load the real resource files and render every message you care about, with Translator::try_format (Errors and fallbacks); the cookbook has a test that compares languages.

#Plural forms, per language

A table-driven test documents which forms a language needs and catches a missing one:

use dxn_i18n::{Args, Message};
use dxn_intl::parse_locale;

let artikli = Message::parse(
    ".input {$n :number} .match $n 0 {{nema artikala}} one {{{$n} artikl}} few {{{$n} artikla}} * {{{$n} artikala}}",
)?;
let hr = parse_locale("hr")?;
for (n, expected) in [(0, "nema artikala"), (1, "1 artikl"), (3, "3 artikla"), (5, "5 artikala"), (21, "21 artikl"), (22, "22 artikla")] {
    assert_eq!(artikli.format(&hr, &Args::new().with("n", n)), expected);
}

#Custom functions

Register the function on a FunctionRegistry, build a MessageFormatter with it and assert both the text and errors.is_empty(), as in Custom functions. Also assert the failure paths: pass the wrong kind of operand and check for FormatError::BadOperand.

Next: Limitations.