Expose MockTransport in a testhelpers package

[lukasschwab]

Problem Statement

I'm integrating Sentry into an existing application, and I want to confirm my application sends expected data to Sentry. A client with a mocked transport layer fits the bill.

Solution Brainstorm

I suggest exposing the TransportMock

It's even duplicated, for exactly the same reason I have: TransportMock is useful for testing a program's interaction with Sentry. The duplicated code has a FIXME comment from :

sentry-go/otel/helpers_test.go

Lines 116 to 122 in e56ac30

	// FIXME(anton): TransportMock is copied from mocks_test.go
	// I don't see an easy way right now to reuse this struct in "sentry" and
	// "sentryotel" packages: it naturally depends on "sentry", but tests in "sentry"
	// package also depend on it, so if we move it to a new package, we'll get an
	// import cycle.
	// Alternatively, it could be made public on "sentry" package, but it doesn't
	// feel right.

cc @tonyo — I think a clear docstring explaining the meaning of TransportMock should be clear enough to prevent someone accidentally using it.

Happy to open a PR implementing the above and removing the duplication 🙇

[tonyo]

I don't mind :) I'm not with Sentry anymore though, so will delegate to the maintainers.