feat(sprocket test): output assertions

[a-frantz]

Describe the problem or feature in addition to a link to the issues.

New user guide for these features - stjude-rust-labs/sprocket.bio#29

There is a strange serde bug which causes the YAML syntax used in this PR to deviate from the syntax used in the serde_yaml_ng docs. See this commit for details 9fbc964 that link to acatton/serde-yaml-ng#14 which links to more information

This is a bit of a "happy accident" bug IMO, as I prefer the alternate syntax used here as opposed to the YAML tag syntax the documentation uses.

I've started adding these to stjudecloud/workflows#263

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[adthrasher]

Just off the top of my head, during our meeting.

Arrays: length(), first(), and last().
Pair: .left() and .right().

[adthrasher]

A few more, though I'm not tied to the naming:

Map: has_key(), count()

Anything more complex is probably going to need to be a custom assertion. The same is true for testing struct types. I'm not sure if we need anything for an enum, I suspect they won't be common outputs and I don't know what you'd want to test other than that the variant is as expected.

[a-frantz]

A few more, though I'm not tied to the naming:

Map: has_key(), count()

count() has been lumped together with Length, which will work on String, Array, and Map.

has_key() is actually more complicated than it might seem, as any WDL primitive type can be the key. So it would actually have to be implemented per-type, which isn't hard, but does complicate the user interface for a set of assertions I don't think are super useful.

Anything more complex is probably going to need to be a custom assertion. The same is true for testing struct types. I'm not sure if we need anything for an enum, I suspect they won't be common outputs and I don't know what you'd want to test other than that the variant is as expected.

I want to think this over some more, but I think you're right. IMO the currently implemented set of assertions is about good for the "essential" assertions for this PR, but it should be easy to extend the set in future PRs.

At least, I'm going to stop implementing more unless someone asks for more specifically. Now time to write tests for all of this, which I'm not looking forward to 😭

[claymcleod]

Left a few comments after reviewing.

[claymcleod]

Whoops, forgot to include these in the last review!