Writing noirc_frontend Unit Tests

Tests live under compiler/noirc_frontend/src/tests/. The root module tests.rs defines helpers and declares submodules organized by topic.

Helpers in tests.rs

Importable from submodules via use crate::tests::{...}.

Compilation

Error Checking with Inline Annotations

Inline Error Annotation Syntax

Used with check_errors(). Error markers go on the line below the code that produces the error:

let src = r#"
    impl Foo::Bar { }
         ^^^^^^^^ Cannot define a trait impl on associated types
         ~~~~~~~~ secondary message here

    fn main() { }
"#;
check_errors(src);

• ^^^ = primary error span + message
• ~~~ = secondary error span + message
• Markers align character-by-character with the code line above

Helpers in test_utils.rs

Importable via use crate::testutils::{...}. Also usable by other crates via the testutils feature.

GetProgramOptions

GetProgramOptions {
    allow_parser_errors: bool,       // default: false
    allow_elaborator_errors: bool,   // default: false — needed for check_errors
    root_and_stdlib: bool,           // default: false — treat as stdlib (enables builtins)
    frontend_options: FrontendOptions,
}

Patterns

Regression test for a bug that should compile (already fixed)

/// Regression test for https://github.com/noir-lang/noir/issues/XXXXX
#[test]
fn descriptive_name() {
    let src = r#"
    // ... Noir program ...
    fn main() {}
    "#;
    assert_no_errors(src);
}

Reproduction test for a bug that should compile (not yet fixed)

/// TODO(https://github.com/noir-lang/noir/issues/XXXXX): remove should_panic once fixed
#[test]
#[should_panic(expected = "Expected no errors")]
fn descriptive_name() {
    let src = r#"
    // ... Noir program ...
    fn main() {}
    "#;
    assert_no_errors(src);
}

Test for expected compile error

#[test]
fn descriptive_name() {
    let src = r#"
    fn main() {
        let x: bool = 42;
                       ^^ expected type annotation
    }
    "#;
    check_errors(src);
}

Gotchas

• Warnings count as errors: getprogram returns warnings (dead code, unused functions) in the Vec<CompilationError>. Unused items cause assertno_errors to fail.

- Fix: mark items pub to suppress "unused" warnings. - pub struct, pub fn for items not called from main(). - If a struct is pub but never constructed, that's still a warning — add pub to fields too, or construct it. - Use the placeholder to suppress unused variable warnings (e.g., an unused x: u32 param becomes x: u32)

• Always include fn main() {}: Programs without main will fail differently.
• No stdlib by default: getprogram doesn't include the stdlib. Use checkerrorswithstdlib or rootandstdlib: true if you need stdlib types/traits.
• Run command: cargo nextest run -p noircfrontend -E 'test(testname)'