Implement SQL unit tests for dataset queries

[lewish]

It should be possible to write a unit test for a dataset query, where mocked data can be provided as input in place of any referenced datasets, and an expected result is also provided.

Awaiting a design doc, will update.

[andrewscarani]

@lewish Is it possible to specify multiple mocks/inputs? And if so, how would one do this?

[BenBirt]

Hopefully it's all clear in https://docs.dataform.co/guides/tests, but yes it is possible to specify multiple named inputs.

[andrewscarani]

@BenBirt It is not clear, because there are no examples of multiple named inputs in that guide and we've tried a few things that did not seem to work. Do you have a working example?

[ryanlim48]

@BenBirt Andrew and I figured out that a semicolon is needed between inputs just by testing out random syntax. It may be helpful to include this in the docs in case others may be running into a similar issue

[BenBirt]

That is completely unexpected, apologies. I've filed #1351