Add a method to RestTestClient API that provides a JsonContentAssert

[donalmurtagh]

See issue #35624

[vpelikh]

I very much miss JsonContent assertions, and this is an awesome change. @donalmurtagh, while you are on it, can you also add the same method to WebTestClient? I think the reactive and imperative test clients should have symmetrical API.

[donalmurtagh]

I very much miss JsonContent assertions

You can still use them (without this new method). The "Current Workaround" section of #35624 shows how.

can you also add the same method to WebTestClient?

That doesn't belong in this PR because #35624 is specifically about adding a JsonContentAssert method to RestTestClient. I'd rather wait and see whether this PR is accepted before adding a similar method to WebTestClient.

I think the reactive and imperative test clients should have symmetrical API.

If that's the case, they should implement a common interface, but they don't.

[rstoyanchev]

@donalmurtagh thanks for the suggested change, but I'll close this for now, and we'll keep the discussion under the issue. What you're bringing up goes beyond JSON content and needs to be considered more broadly.

This PR and the branch is still here for us to refer to.