testutils: use a rows parser for test comparisons

[vmg]

Description

A pretty common pattern in Vitess end2end tests is comparing the results of a query against a hardcoded string that represents a %v-formatted syntax of the rows we're expecting. It usually looks something like this:

assert.Equals(t, "[[INT64(1) INT64(8)] [INT64(1) INT64(9)]]", fmt.Sprintf("%v", rows))

This is all well and good! There are several helpers that print the rows directly without having to call Sprintf and that compare them directly. I like the literal strings to define the expectations for row results.

However, shit gets funky when testing queries whose result from Vitess/MySQL doesn't have consistent ordering. How can we handle such comparisons when the sql.Rows returned by Vitess can have any ordering but our expectation string is obviously fixed?

This is how it's done at the moment:

actual := fmt.Sprintf("%v", qr.Rows)
assert.Equal(mcmp.t, utils.SortString(expected), utils.SortString(actual))

This... doesn't seem generally safe? Is SortString doing something very smart here? If you look at its implementation, you can see that, huh, it's doing the opposite of something very smart. It re-arranges all the individual bytes of the string alphabetically and returns that.

So, for a rows string like "[[INT64(1) INT64(8)] [INT64(1) INT64(9)]]", it generates " (((())))114444666689IIIINNNNTTTT[[[]]]" and compares that against the other formatted rows. The many ways in which this is not a generally safe way to compare row results are left to the reader. I bet you can come up with hundreds!

So, onto the actual content of the PR: this PR introduces a generally safe way to compare unordered sets of rows! 🎉

It works by implementing a simple Lexer + Parser that can take a "row string" like the ones we use in our tests and converts it into an actual sql.Row (i.e. a []sql.Value slice). Then, it performs an ordering-agnostic comparison of the sql.Value entries against the values returned by Vitess/MySQL. It works very well in practice! We've tested it internally at PlanetScale.

I'm hoping this will catch some actual mismatches in our end2end tests down the road.

Related Issue(s)

Checklist

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Deployment Notes

[vitess-bot]

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[systay]

This is really great. Thank you!

[vmg]

🎉