test(eventhubs): cover consumer receive options

[Johnathan W (j7nw4r)]

Summary

This change adds tests/eventhubs_receive_options.rs with six live tests for the consumer receive options. The tests cover a custom prefetch value, the smallest usable prefetch value, the receive_timeout semantics on an idle partition and on a slow partition, the consumer with_instance_id option, and the producer with_application_id option.

Motivation

Prefetch sets the credit that the receiver grants to the AMQP link, so a wrong value can stall a stream or waste memory, and no test sets OpenReceiverOptions::prefetch today. The receive timeout controls what happens when a partition is idle; five tests set receive_timeout and none assert it. ConsumerClientBuilder::with_instance_id has no caller in the repository. Part of #4886.

Changes

• Add tests/eventhubs_receive_options.rs with six #[recorded::test(live)] tests.
• Cover a custom prefetch of 3 and the smallest usable prefetch of 1, and assert that every event of the run arrives in order.
• Assert that an idle partition yields a receive-timeout error whose chain reaches std::io::ErrorKind::TimedOut, that it arrives inside a timing window, and that the stream then ends.
• Assert that a stream fed slower than the receive timeout is not truncated, which pins the documented per-delivery meaning of the option.
• Cover ConsumerClientBuilder::with_instance_id and ProducerClientBuilder::with_application_id.
• Tag every event with a per-run marker, so each test asserts on its own events and tolerates the foreign traffic that shares a partition.

Test plan

• CARGO_BUILD_JOBS=1 RUSTFLAGS=-Dwarnings cargo test --no-run --package azure_messaging_eventhubs exits 0. CI sets RUSTFLAGS: "-Dwarnings", so this gate catches an unused import, an unused constant, or an uncalled helper.
• cargo test --package azure_messaging_eventhubs --test eventhubs_receive_options -- --test-threads=1 reports 0 passed; 0 failed; 6 ignored, because the tests are live-gated.
• cargo test --package azure_messaging_eventhubs -- --test-threads=1 reports 196 passed and 0 failed across all targets.
• cargo fmt --package azure_messaging_eventhubs -- --check, cargo clippy --package azure_messaging_eventhubs --all-features --all-targets with -Dwarnings, and cargo doc --package azure_messaging_eventhubs --all-features --no-deps with -Dwarnings all exit 0.
• npx cspell lint --config ./.vscode/cspell.json --no-must-find-files --no-gitignore --root . <the new file> reports Files checked: 1, Issues found: 0.
• No red proof accompanies these tests, and none is possible. They pin behavior that the shipped source already has, this change touches no source file, and a live-gated test cannot run without a namespace. A throwaway unit test invented to produce a failing run would prove nothing.

Assumptions and divergences from the .NET tests

• The small prefetch value is 1, not 0. prefetch maps to ReceiverCreditMode::Auto(n), and a value of 0 gives the link no credit and stalls the reader, so no test pins that path. .NET maps PrefetchCount = 0 to AutoSendFlow = false and issues credit per read instead, which this crate cannot express through OpenReceiverOptions. A follow-up issue should decide whether prefetch: Some(0) ought to select ReceiverCreditMode::Manual.
• The idle test asserts the current Rust behavior, which is that the stream yields an error and then ends. .NET ReadEventOptions.MaximumWaitTime yields a repeatable empty event and never ends the enumeration, so a direct port of ConsumerRespectsTheWaitTimeWhenReading could not pass. A follow-up issue should decide whether the Rust stream ought to surface an idle interval in band instead.
• The producer test uses with_application_id, because ProducerClientBuilder has no with_instance_id. Adding one is a public API change and is out of scope for a test change. A follow-up issue should decide whether the producer needs identifier parity with the consumer.
• The producer test overlaps existing coverage in tests/eventhubs_producer.rs on purpose, so the third item in [Event Hubs] Add live tests for consumer receive options #4891 maps to a named test.
• The two prefetch tests cannot detect a regression that silently drops prefetch and substitutes the default of 300, because the negotiated link credit is not observable through the public API. They do catch a broken credit replenishment and a rejected small credit.

Closes #4891.

Live validation

Every test here ran against a live Event Hubs namespace on 2026-08-20: 6 passed, 0 failed.

Command: AZURE_TEST_MODE=live cargo test --package azure_messaging_eventhubs --test eventhubs_receive_options -- --test-threads=1.

One assertion was widened after that run. The receive timeout cause could not be downcast to std::io::Error, because the receiver wraps it in Box::new at common/recoverable/receiver.rs:129 and azure_core::Error::new boxes again, so the stored type is Box<std::io::Error>. The test accepts either shape, so it keeps passing once the extra box goes away. The extra box is tracked in #5098.

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