Interesting! I guess it's pretty easy to convert this pseudo-JSON to RESP, althought it adds some non-trivial code to the testing. My first though is that single-quoted stings are not allowed in JSON. :)

My second thought is that it might be possible to construct a parse tree structure that is readable and easy to serialize to RESP, without parsing. Ideally, test code should be trivial, so there is no doubt if there's a bug, is it a bug in the test code or in the real implementation?

Here is a reply literal with the first slot range (untested). It's much bigger than the pseudo-JSON obviously.

valkeyReply reply = {.type = VALKEY_REPLY_ARRAY, .elements = 3, .element = (valkeyReply[]){
    {.type = VALKEY_REPLY_ARRAY, .elements = 4, .element = (valkeyReply[]){
        {.type = VALKEY_REPLY_INTEGER, .integer = 0},
        {.type = VALKEY_REPLY_INTEGER, .integer = 5460},
        {.type = VALKEY_REPLY_ARRAY, .elements = 4, .element = (valkeyReply[]){
            {.type = VALKEY_REPLY_STRING, .str = "127.0.0.1"},
            {.type = VALKEY_REPLY_INTEGER, .integer = 30005},
            {.type = VALKEY_REPLY_STRING, .str = "e7d1eecce10fd6bb5eb35b9f99a514335d9ba9ca"},
            {.type = VALKEY_REPLY_ARRAY, .elements = 2, .element = (valkeyReply[]){
                {.type = VALKEY_REPLY_STRING, .str = "hostname"},
                {.type = VALKEY_REPLY_STRING, .str = "localhost"} 
            }
        }
    },
    ...
};

Interesting, are there similar tests in the valkey repo?

No, but similar nested struct literals, in some modules used for module API tests. The one for testing key specifications IIRC.

The tests for replies like CLUSTER SLOTS use Tcl code which is compact but most often doesn't check the types.

A nested reply like that is a Tcl list on the form

{{0 5460 {127.0.0.1 30001 abcde123456 {hostname localhost} ...

Hum, I've been trying to get something nicer to work, but have failed so far.
The problem I face is that .element is a valkeyReply **.
Not sure if splitting up the initialization makes it readable, maybe a macro can be used in some way..

Let's use the pseudo-JSON then. It's pretty simple.

I'll merge this variant then.