Robustness checks for DiD I am currently looking at a DiD model to evaluate the impact of a policy on ethnic and non ethnic people in the EU. I have done the regression and got the results.
I have only two time periods but 10 countries. I was wondering what robustness checks I could run? I know for my model the parallel trends assumptions is not possible so what robustness checks could I do?
Much of what I have read on or come across is running a placebo test but confused on what that exactly means.

You can perform a placebo test by changing the treatment group.  You are actually doing:
$$Y_{it} = \beta_1 + \beta_2 (\text{treat}_i) + \beta_3 (\text{time}_t) + \rho (\text{treat}_i \cdot \text{time}_t) + \epsilon_{it}$$
and checking if $ \rho$ is statiscally significant.  Instead of using your real treatment group, in a placebo test you change the treatment dummy (ethnic) to something like gender (or any other variable that you have). The effect should not be significant
