split scale tests into separate files

[kubikowski]

Description:

There is a fundamental design decision in the Jest testing framework, such that all unit test files are run in sandboxed runtimes from each other. And there is no real way of sharing initialized TS between those isolated runtimes.

This presents a couple of issues, but the foremost is that: even if we set jest to runInBand (run the test files serially) they will each need to run the setup files. And the scale test setup itself takes a substantial amount of time to initialize, some ~15s. So, by separating the scale test files, we would be adding ~150s of initialization to the overall scale testing time. This is unacceptable.

In order to maintain a singular initialization, we are still running all scale tests from inside a singular scale.test.ts. To do this, instead of writing a describe at the top level of each scale test file, we are instead exporting the function which would run in such a describe. And then running all of the describes themselves from scale.test.ts.

Resources:

• Allow to share global state between tests from globalSetup jestjs/jest#7184
• Add Global Setup/Teardown APIs jestjs/jest#4716