Theorem (Portmanteau): Let $g: \real^d \to \real$. The following conditions are equivalent:

(a) $\x_n \inD \x$.
(b) $\Ex g(\x_n) \to \Ex g(\x)$ for all continuous functions $g$ with compact support.
(c) $\Ex g(\x_n) \to \Ex g(\x)$ for all continuous bounded functions $g$.
(d) $\Ex g(\x_n) \to \Ex g(\x)$ for all bounded measurable functions $g$ such that $g$ is continuous almost everywhere.

Proof: van der Vaart, Asymptotic Statistics (1998), Lemma 2.2.

The Portmanteau theorem can include several more equivalence conditions; van der Vaart provides seven.