Even after a magnum opus on the DSL LMAX uses for acceptance tests, there’s one crucial feature that I haven’t mentioned: the use of aliases to allow tests to use simple, meaningful names while ensuring that uniqueness constraints are met.

Creating a user with our DSL looks like:

registrationAPI.createUser("user");

You might expect this to create a user with the username ‘user’, but then we’d get conflicts between every test that wanted to call their user ‘user’ which would prevent tests from running safely against the same deployment of the exchange.

Instead, ‘user’ is just an alias that is only meaningful while this one test is running. The DSL creates a unique username that it uses when talking to the actual system. Typically this is done by adding a postfix so the real username is still reasonably understandable e.g. user-fhoai42lfkf.

We do the same thing for instruments, venues, currencies and anything else that needs unique names.

This relatively simple trick gives us a great deal of isolation between tests that may run against the same server instance, even allowing us to run the same test multiple times without interfering with itself.