encoding/jsonschema: add a few tests
This adds a few tests for behavior that's about to change:
- an empty open list that could be encoded without an `items` keyword
- a `null` value that could be encoded with `type` rather than `const`
Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I652a6e684f95d6991366eb571030fd4b05942481
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1224281
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>