31 lines
1.4 KiB
Markdown
31 lines
1.4 KiB
Markdown
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---
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summary: "Minitest 6 removed Minitest::Mock from core — require 'minitest/mock' raises LoadError; the API lives in the separate minitest-mock gem, and pinning minitest < 6 double-loads constants."
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tags:
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- type/reference
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- tool/minitest
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- domain/testing
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scope: global
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date: 2026-07-16
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---
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# Minitest 6 extracted Minitest::Mock from core
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Under minitest 6.x (observed on 6.0.6, Ruby 4.0.2), `require "minitest/mock"` raises
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`LoadError: cannot load such file -- minitest/mock`. The mock/stub API was extracted from
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the core gem into a separate **`minitest-mock`** gem. Test suites written against minitest
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5.x that use `Minitest::Mock` or `Object#stub` break on load once 6.x is the activated
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version.
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**What doesn't work:** pinning `gem "minitest", "< 6"` in a test helper. If minitest 6 is
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already activated (it ships as a default gem), the pin loads 5.x *alongside* 6.x and floods
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output with `already initialized constant Minitest::VERSION` / `Runnable::SIGNALS` warnings
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— two versions' constants coexist.
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**Fixes, in order of preference:**
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1. Add the `minitest-mock` gem (Gemfile or `gem install minitest-mock`) — restores the old
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`require "minitest/mock"` path.
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2. Migrate the tests off `Minitest::Mock` (hand-rolled fakes/stubs — often cleaner anyway).
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Discovered 2026-07-16 while diagnosing a pre-existing failure in cc-plugins'
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`cc-architect` test suite (`test_runtime_verifier.rb`, 6 errors).
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