Otel TracerProvider Embedding hard to auto-mock.

[rbtcollins]

Description

There is a marker interface 'embedded.TracerProvider' with unexported methods https://pkg.go.dev/go.opentelemetry.io/otel/trace/embedded#TracerProvider

With a testify style mock, the Mock does not implement otel.trace.TracerProvider unless the generated code is edited to add that same embedded interface.

Perhaps there is another way of doing it; I'm not sure, but I thought you'd like to know :>

Having some way to add some code to the generated mock struct definition would perhaps be enough to solve this.

[LandonTClipp]

This is something that has been brought up before: #1031

The cleanest way to go about this is to probably change the testify template to allow users to inject arbitrary code into specific places in the template. Users would specify something like:

template-data:
    struct-block: "trace.TracerProvider"

You'd also need a way to add more imports here: https://github.com/vektra/mockery/blob/v3/internal/mock_testify.templ#L15-L20

Which again could be specified in config. I want to highlight the fact that you can actually do all of these changes TODAY without needing to upstream anything. If you copy-paste the testify template from source and make these modifications, you can give mockery the path to your new template: https://vektra.github.io/mockery/latest/template/#template-file