Take the real line $\mathbb R$. Instead of the usual uniform structure on $\mathbb R$, we will say that each neighborhood of the diagonal of $\mathbb R \times \mathbb R$ is an entourage. This defines a uniform space.
This space definitely is not complete. What is this space's Hausdorff completion? (A follow up question is to ask the same thing for $\mathbb R^n$.)