Centralize component install failure message in tests

[leynos]

Summary

• Centralizes the component install failure message into a shared constant and uses it across tests to improve error handling verification and reduce brittle string literals.

Changes

Testing

• Add COMPONENT_INSTALL_FAILURE_MESSAGE constant in installer/src/toolchain/tests/failure_mocks.rs
• Use COMPONENT_INSTALL_FAILURE_MESSAGE in setup_component_add_failure_mocks_inner when returning stderr output
• Update is_component_install_failed to check for COMPONENT_INSTALL_FAILURE_MESSAGE
• Update tests in installer/src/toolchain/tests/mod.rs to import and reference COMPONENT_INSTALL_FAILURE_MESSAGE instead of the literal string
• Adjust test expectations to use the new constant

Why

• Removes duplication and potential drift between tests by consolidating the failure message into a single shared constant
• Improves maintainability and robustness of error handling verification in tests

Test plan

• Run cargo test (workspace) to ensure all tests pass, with emphasis on toolchain/install-related tests
• Specifically verify tests that previously asserted on the string "component failed" now use the centralized constant

Notes

• The COMPONENT_INSTALL_FAILURE_MESSAGE constant is pub(super) to restrict visibility to the test module scope
• No production code behavior changed; this is a test-only refactor to improve reliability and readability

◳ Generated by DevBoxer ◰

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📎 Task: https://www.devboxer.com/task/3af976c2-4ae8-40dc-9702-a8f52931adee

Summary by Sourcery

Tests:

• Introduce a shared COMPONENT_INSTALL_FAILURE_MESSAGE constant for mocked stderr output in toolchain installer tests and update assertions and helpers to use it.

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Centralizes the component install failure message into a single shared constant used by failure mocks and assertions in toolchain installer tests, improving consistency and reducing duplicated string literals.

File-Level Changes

Change	Details	Files
Introduce a shared constant for the component install failure message and use it in failure mocks and helper logic.	Define pub(super) COMPONENT_INSTALL_FAILURE_MESSAGE constant holding the failure message string Update mocked command runner setup to return stderr using the shared constant Update is_component_install_failed helper to check message contents using the shared constant instead of a literal	installer/src/toolchain/tests/failure_mocks.rs
Update toolchain installer tests to rely on the shared failure message constant instead of hard-coded strings.	Import and use COMPONENT_INSTALL_FAILURE_MESSAGE when constructing failing command runner output Adjust error pattern-matching assertions to check message contents using the shared constant	installer/src/toolchain/tests/mod.rs

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