public synchronized void nextDelay(final Duration delay) {
        assertTimeoutPreemptively(
                ofSeconds(1),
                () -> assertDoesNotThrow(() -> this.delays.put(delay.toMillis())),
                "Failed to queue delay");
    }
The next call will wait the configured amount of time before completing. Allows exactly one call to process. May
only queue up to one call.

@param delay The delay to wait for.
tests/src/test/java/net/devh/boot/grpc/test/server/WaitingTestService.java