Macro subtest 

macro_rules! subtest {
    (|$($param:ident : $ty:ty),* $(,)?| $body:block) => { ... };
}

Creates an isolated subtest closure with its own failure tracking.

Within a subtest, assertions (expect_*!, assert_*!, unwrap_*!) record failures to the subtest’s local status flag rather than the enclosing test’s flag. Hard assertions (assert_*!, unwrap_*!) return false early from the subtest without returning from the enclosing test.

Returns bool: true if all assertions in the subtest passed, false otherwise.