AFAICT, impeller_unittests (the non-golden kind) are run on CI with Vulkan validation. However, these don't render frames. So only non-frame assertions and validations are checked. Specifying --playground_timeout_ms=0 along with --enable_vulkan_validation will make the playgrounds render one and only one frame. This ought to be enough to get us a whole lot more coverage of Vulkan issues.