public ExecutorConfig setPoolSize(final int poolSize) {
        if (poolSize <= 0) {
            throw new IllegalArgumentException("poolSize must be positive");
        }
        this.poolSize = poolSize;
        return this;
    }
@Test(expected = IllegalArgumentException.class)
    public void shouldNotAcceptNegativeCorePoolSize() {
        new ExecutorConfig().setPoolSize(-1);
    }