assert-struct-guidance

name	assert-struct-guidance
description	Always use this skill before writing any test code in the Toasty repository
depends-on	assert-struct

The assert-struct crate helps to write concise assertions for the values of struct fields.

assert_struct! rule

Use whichever form produces fewer characters and the same test coverage.

// assert_eq! wins — single field
assert_eq!(foo.name, "hello");

// assert_struct! wins — multiple fields in one call
assert_struct!(foo, _ { name: "hello", age: 30 });
// vs. assert_eq!(foo.name, "hello"); assert_eq!(foo.age, 30);

// assert_eq! wins — you have the whole value
assert_eq!(result, Foo::default());

assert_struct! quick reference

Patterns compose freely. Use _ for wildcard struct (no import needed), .. for partial match:

assert_struct!(val, _ { field: "text", count: > 0, flag: true, .. });
assert_struct!(val, _ { opt: Some(42), res: Ok("ok"), .. });
assert_struct!(val, _ { items: [1, 2, ..], tags: #("a", "b", ..), .. });
assert_struct!(val, _ { nested.child.x: >= 0, .. });  // dot-path shorthand
assert_struct!(val, _ { items.len(): 3, .. });         // method call

Operator patterns at leaves avoid importing types:

// Instead of:  field: SomeEnum::Variant(42)
// Write:        field: == expected_var

The full pattern grammar can be found in the LLM.txt resource within this skill.

assert_struct! formatting

rustfmt does not format assert_struct! bodies. You are responsible for formatting them manually, using the same rules rustfmt would apply to equivalent Rust code.

One-liner: If the entire call fits on one line within the column limit (~100 chars), keep it on one line.

assert_struct!(resp, _ { rows: Rows::Count(1), .. });

Multi-line: When breaking across lines, treat the macro body like a struct literal or match arm — indent the contents by 4 spaces relative to the assert_struct! call, and put the closing }); on its own line.

assert_struct!(op, Operation::QuerySql(_ {
    stmt: Statement::Update(_ {
        target: UpdateTarget::Table(== foo_table_id),
        assignments: #{ 1: _ { expr: == "new", .. } },
        ..
    }),
    ..
}));

When the macro syntax differs from Rust (e.g. #{ .. } for map patterns, == expr leaf operators, dot-path keys like items.len():), use your best judgment to apply equivalent rustfmt rules: align commas consistently, indent nested levels, and never leave trailing whitespace.