apply us-east-1 as default region if not set by user in with_test_defaults_v2()

[aajtodd]

Motivation and Context

• aws-smithy-mocks mock_client does not support clients that don't have a region #4265
• docs(aws-smithy-mocks): Document that client packages should enable test-util feature, provide sample Cargo.toml #4189

Description

• Adds a new with_test_defaults_v2() method to all clients supporting region configuration. This new method applies us-east-1 as default region if not set by user. This allows aws-smithy-mocks to work for non AWS SDK generated clients. This is only set as the default if a user has not already supplied one.
  • NOTE: We are choosing to add a new method here for backwards compatibility concerns (our own generated endpoint tests break because of precedence problems between endpoint rules and with_test_defaults).
• Clarify test-util feature requirement when using aws-smithy-mocks.

Checklist

• For changes to the smithy-rs codegen or runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "client," "server," or both in the applies_to key.
• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

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[landonxjames]

Some questions on the README, no blockers

[landonxjames]

I know its kind of implicit in the example below that test-util should only be enabled for [dev-dependencies], but should we make that explicit and warn users only to use those features for testing?

[rcoh]

This happens so frequently that I wonder if we should design a really nice error where the mock_client invokes a macro we define in the crates and if test-util isn't enabled it uses compile_fail! To give a precise error.

Can't do it here obviously since we'd need to add that macro first in the generated crates

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[rcoh]

Is it worth a BMV for this or other opt-out? I feel like there is a very high probability that someones unit test will be broken by this and although the fix won't be hard they might appreciate a way to hold back to keep their tests working

[aajtodd]

Our own unit tests are broken by this and I'm not sure whether we want to ship this right now as we have introduced a precedence problem for defaults between with_test_defaults and endpoint builtins.

---

Generated test code:

// Code generated by software.amazon.smithy.rust.codegen.smithy-rs. DO NOT EDIT.
#![cfg(feature = "test-util")]
#[::tokio::test]
async fn operation_input_test_test_operation_1() {
    /* documentation: region should fallback to the default */
    /* builtIns: {} */
    /* clientParams: {} */
    let (http_client, rcvr) = ::aws_smithy_http_client::test_util::capture_request(None);
    let conf = {
        #[allow(unused_mut)]
        let mut builder = endpoint_test_service::Config::builder().with_test_defaults().http_client(http_client);
        builder.build()
    };
    let client = endpoint_test_service::Client::from_conf(conf);
    let _result = dbg!(
        client
            .test_operation()
            .set_bar(::std::option::Option::Some(
                endpoint_test_service::types::Bar::builder()
                    .set_f(::std::option::Option::Some("blah".to_owned()))
                    .build()
            ))
            .send()
            .await
    );
    let req = rcvr.expect_request();
    let uri = req.uri().to_string();
    assert!(
        uri.starts_with("https://prod.us-east-2.api.myservice.aws.dev/"),
        "expected URI to start with `https://prod.us-east-2.api.myservice.aws.dev/` but it was `{}`",
        uri
    );
}

• Model: https://github.com/smithy-lang/smithy-rs/blob/3c11815e5e4d0ec8c048d4bde7af94b710039672/aws/sdk-adhoc-test/models/single-static-endpoint.smithy

failure:

running 1 test
test operation_input_test_test_operation_1 ... FAILED

failures:

---- operation_input_test_test_operation_1 stdout ----
[endpoint-test-service/rust-client-codegen/tests/endpoint_tests.rs:15:19] client.test_operation().set_bar(::std::option::Option::Some(endpoint_test_service::types::Bar::builder().set_f(::std::option::Option::Some("blah".to_owned())).build())).send().await = Ok(
    TestOperationOutput {
        _request_id: None,
    },
)

thread 'operation_input_test_test_operation_1' panicked at endpoint-test-service/rust-client-codegen/tests/endpoint_tests.rs:28:5:
expected URI to start with `https://prod.us-east-2.api.myservice.aws.dev/` but it was `https://prod.us-east-1.api.myservice.aws.dev/foo`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    operation_input_test_test_operation_1

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

---

this test is generated by: https://github.com/smithy-lang/smithy-rs/blob/2016a67af3beeb4c976da9fb3d867f15822e[…]/amazon/smithy/rustsdk/endpoints/OperationInputTestGenerator.kt
Interestingly it shows nothing for builtins

but effectively it's relying on the default builtin value of us-east-2which it would not be now because with_test_defaults sets a different default when unset

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.