The Vulkan Conformance Tests Suite (CTS) is a set of tests used to verify the conformance of an implementation. A conformant implementation shows that it has successfully passed CTS and it is a valid implementation of Vulkan. A list of conformant products is publicly available.
Any company with a conformant implementation may freely use the publicly released Vulkan specification to create a product. All implementations of the Vulkan API must be tested for conformance in the Khronos Vulkan Adopter Program before the Vulkan name or logo may be used in association with an implementation of the API.
The Vulkan CTS source code is freely available and anyone is free to create and add a new test to the Vulkan CTS as long as they follow the Contributing Wiki.
An application can query the version of CTS passed for an implementation using the VkConformanceVersion property via the VK_KHR_driver_properties extension (this was promoted to core in Vulkan 1.2).