Add Spector test coverage for CommonPropertiesErrorClient methods

[Copilot]

Adds missing test coverage for create_for_user_defined_error() and get_for_predefined_error() methods in CommonPropertiesErrorClient.

Changes

• New test file: common_properties_error_client_test.rs under packages/typespec-rust/test/spector/azure/resource-manager/common-properties/tests/
  • Tests use ConfidentialResource model and validate error response http code
  • Follows existing test patterns from common_properties_managed_identity_client_test.rs (FakeTokenCredential, helper functions, assertion structure)
  • Designed to run with Spector mock server on localhost:3000

No modifications to generated source code or emitter.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add Spector test coverage for the CommonPropertiesErrorClient's methods</issue_title>
<issue_description>1. Do not modify the generated rust source code (in src/generated), only modify the emitter code (in /packages/typespec-rust/src/) if necessary
2. The test for the common-properties does already exist (under packages/typespec-rust/test/spector/azure/resource-manager/common-properties/tests/). Add a file called common_properties_error_client_test.rs there, and add tests for two methods - create_for_user_defined_error() and get_for_predefined_error().</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add Spector test coverage for the CommonPropertiesErrorClient's methods #821

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[Copilot]

Pull request overview

Adds Spector integration tests for the CommonPropertiesErrorClient operations in the common-properties ARM test crate, exercising the error paths for two previously untested client methods.

Changes:

• Adds a new integration test file covering create_for_user_defined_error() and get_for_predefined_error().
• Verifies the returned azure_core::Error has the expected HTTP status codes (400/404).

[heaths]

I like that it's generating error models; but, in what cases should we expect it to generate a TryFrom now? I don't see that in here. I thought we want to if they actually may return a custom error instead.

[jhendrixMSFT]

This should be tcgc.isAzureCoreModel(model) (will post a fix shortly).