Clarify purpose of handler_stream_test.go

[Hirochon]

Clarify that the sole purpose of the test in handler_stream_test.go is to verify a safety property of the ClientStream iterator. A similar testing strategy isn't worthwhile for ServerStream or BidiStream, because they're not iterators.

[akshayjshah]

Hi @Hirochon - thank you for opening this PR! Unfortunately, I'd rather not merge the extra tests you've added. The existing test verifies that the ClientStream iterator allocates a new message for each iteration. (It's a regression test for a fix we made last year.) There's no need for similar tests of ServerStream or BidiStream, because they're not iterators. All three stream types are tested much more extensively in connect_ext_test.go.

However, this PR did highlight that the existing test isn't well-documented. I've pushed some commits to your branch to remove the extra tests and add better documentation. I'm going to amend the PR title and description and merge this in, so that you're still credited in the next set of release notes.

[akshayjshah]

@Hirochon's original PR description, for posterity:

This pull request adds tests for ServerStream and BidiStream, in addition to the existing tests for ClientStream.

Specifically, the tests cover the following cases:

• TestServerStream: Tests the Send method of ServerStream.
• TestBidiStream: Tests the Receive and Send methods of BidiStream.

I have implemented the tests using the nopServerStreamingHandlerConn and nopBidiStreamingHandlerConn structs, which are similar to the nopStreamingHandlerConn struct used in the existing tests for ClientStream. I have also made sure that the new tests are consistent with the existing test code, so that the overall test suite feels consistent and cohesive.

[Hirochon]

Hi @akshayjshah
I understand your concerns regarding the extra tests I added. Thank you for explaining the purpose of the existing test and the extensive testing of the other stream types. I appreciate your efforts to improve the documentation and am glad that I could help in this regard.