public Stopwatch start() {
        Assert.isTrue(!isRunning, "This stopwatch is already running.");
        isRunning = true;
        startTick = ticker.read();
        return this;
    }
Starts the stopwatch.

@return this {@code Stopwatch} instance
@throws IllegalStateException if the stopwatch is already running.
lts-core/src/main/java/com/github/ltsopensource/core/commons/concurrent/limiter/Stopwatch.java