How to get the correct MeterProvider in extension tests

[bryce-anderson]

I'm writing a custom extension and using the AbstractHttpClientTest to test it. This extension just automatically installs some filters that are compiled against the opentelemetry-api package (eg, not a part of the extension build and thus not using the agents shaded types). The AbstractHttpClientTest.httpClientMetrics() test always fails and it looks like it's because I'm always getting the noop MeterProvider. This appears to be because I'm getting the vanilla ApplicationOpenTelmetry from GlobalOpenTelemetry.get() which uses the default getMeterProvider() method that returns the noop provider.

It looks like the agent itself has ApplicationOpenTelemetry127 that addresses this which will be reflectively loaded if it's on the classpath, but it doesn't appear to be part of the agent testing package. Have I potentially misconfigured something that is causing this to not be available during testing?