This PR decreases test execution time for the test_client test suite by about 2 whole minutes (132 seconds, I think).

It does that by extracting the aggregate_metrics function and, instead of waiting for the client to actually send metrics, just checking what the metrics would be aggregated to.

In doing so, it might be worth adding another test to ensure that metrics are actually sent, but we may or may not already have this elsewhere.

Type of change

Please delete options that are not relevant.

• Refactor of tests

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• Unit tests

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules