Struct Clock 

pub struct Clock(/* private fields */);

An injectable source of “now”. Cloning is cheap and, for a test clock, shares the same controllable offset — so a handle handed to a test moves in lockstep with the clock the handler resolves.

Implementations

impl Clock

pub fn system() -> Self

The real clock: now() reads SystemTime::now() each call. This is what App::new() provides by default.

pub fn test() -> Self

A controllable test clock. The base is SystemTime::now() at creation — tests assert on movement (advance/set), not on an absolute base, so a realistic starting instant is fine and avoids surprising callers that subtract UNIX_EPOCH.

pub fn now(&self) -> SystemTime

The current instant. For Clock::system this is the live system clock; for Clock::test it is base + accumulated offset.

pub fn advance(&self, d: Duration)

Move a test clock forward by d. Panics on a system clock — advancing real time is meaningless, and silently ignoring it would hide a test bug.

pub fn set(&self, when: SystemTime)

Pin a test clock to an absolute instant. Panics on a system clock for the same reason as advance. Useful for cron/expiry tests that need a specific wall-clock time rather than a delta.

Trait Implementations

impl Clone for Clock

fn clone(&self) -> Clock

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.