tests: speed up slow tests

[bevanjkay]

This PR optimises some of the slowest tests in the suite, without undermining their accuracy.

1. Migrator Spec - use zip fixture instead of dmg - avoids the need to mount the image.

Benchmark

Benchmark 1: before Time (mean ± σ): 10.638 s ± 1.252 s [User: 1.239 s, System: 1.053 s] Range (min … max): 7.639 s … 12.059 s 10 runs

Benchmark 2: after
Time (mean ± σ): 2.560 s ± 0.094 s [User: 1.172 s, System: 0.933 s]
Range (min … max): 2.497 s … 2.743 s 10 runs

Summary
after ran
4.16 ± 0.51 times faster than before

2. Tab Spec - use a file:// url, to prevent the spec from trying to use curl.

Benchmark

Benchmark 1: before Time (mean ± σ): 19.561 s ± 0.207 s [User: 4.323 s, System: 0.955 s] Range (min … max): 19.326 s … 19.981 s 10 runs

Benchmark 2: after
Time (mean ± σ): 5.413 s ± 0.108 s [User: 4.274 s, System: 0.895 s]
Range (min … max): 5.308 s … 5.647 s 10 runs

Summary
after ran
3.61 ± 0.08 times faster than before

3. spec_helper - stub the timeout so there isn't any unnecessary sleep during the test run.

Benchmark

Benchmark 1: before Time (mean ± σ): 4.052 s ± 0.046 s [User: 1.168 s, System: 0.613 s] Range (min … max): 3.986 s … 4.125 s 10 runs

Benchmark 2: after
Time (mean ± σ): 1.933 s ± 0.019 s [User: 1.128 s, System: 0.557 s]
Range (min … max): 1.908 s … 1.964 s 10 runs

Summary
after ran
2.10 ± 0.03 times faster than before

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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I used claude-code with Opus 5 to find the slowest tests, and speed them up. I verified the performance improvement and the changes that were made.

[MikeMcQuaid]

Thanks, good catch!

[Copilot]

Pull request overview

This PR reduces overall test suite runtime by adjusting a few slow specs to avoid expensive operations (disk image mounting, external network tooling, and real backoff sleeps) while keeping the same behavioral assertions.

Changes:

• Update the Cask migrator spec to use a ZIP-based cask fixture instead of a DMG-based fixture to avoid DMG mounting overhead.
• Update the Tab spec to use a file:// URL in the relevant formula fixtures to avoid triggering curl-related download strategy behavior during Tab.create.
• Stub Utils.sleep in spec_helper so tests don’t actually wait during Utils.exponential_backoff_sleep (and similar) calls.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Library/Homebrew/test/cask/migrator_spec.rb	Switches the “new cask” fixture to a ZIP variant and updates expectations accordingly to avoid DMG mount costs.
Library/Homebrew/test/tab_spec.rb	Uses file:// URLs in the specific Tab.create scenarios to avoid curl/tooling overhead during downloader setup.
Library/Homebrew/test/spec_helper.rb	Globally stubs Utils.sleep to eliminate real backoff sleeps during the test suite.

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