From 50a352c0c0cd151f12aa35790bdcb2d52c5d5249 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Thu, 23 Nov 2023 16:11:41 +0900
Subject: [PATCH] Fix an error for `Minitst/AssertOperator` and
 `Minitest/RefuteOperator`

This PR fixes the following error for `Minitst/AssertOperator` and `Minitest/RefuteOperator`
when running with Ruby 2.7:

```console
$ ruby -v
ruby 2.7.8p225 (2023-03-30 revision 1f4d455848) [x86_64-darwin19]

$ bundle exec rake

Finished in 2.522134s, 15.0666 runs/s, 18.6350 assertions/s.

  1) Error: RefuteOperatorTest#test_registers_offense_when_using_refute_with_operator_method_and_message:
FrozenError: can't modify frozen String: "expected, :<, actual"
    /Users/koic/src/github.com/rubocop/rubocop-minitest/lib/rubocop/cop/minitest/refute_operator.rb:46:
    in `build_new_arguments'
    /Users/koic/src/github.com/rubocop/rubocop-minitest/lib/rubocop/cop/minitest/refute_operator.rb:30:
    in `on_send'
```

And it introduces CI for the oldest RuboCop version still supported,
implementing a workflow for regression testing that is similar to the one found a
https://github.com/rubocop/rubocop-rails/commit/c9acb7a.
---
 .github/workflows/test.yml                    | 32 +++++++++++++++++++
 ...est_assert_operator_and_refute_operator.md |  1 +
 lib/rubocop/cop/minitest/assert_operator.rb   |  2 +-
 lib/rubocop/cop/minitest/refute_operator.rb   |  2 +-
 4 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 .github/workflows/test.yml
 create mode 100644 changelog/fix_error_for_minitest_assert_operator_and_refute_operator.md

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 00000000..af69493d
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  oldest_supported_rubocop:
+    runs-on: ubuntu-latest
+    name: The oldest supported RuboCop version
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use the oldest supported RuboCop
+        run: |
+          sed -e "/gem 'rubocop', github: 'rubocop\/rubocop'/d" -i Gemfile
+          cat << EOF > Gemfile.local
+            gem 'rubocop', '1.39.0' # Specify the oldest supported RuboCop version
+          EOF
+      - name: set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.7
+          bundler-cache: true
+      - name: test
+        run: bundle exec rake
diff --git a/changelog/fix_error_for_minitest_assert_operator_and_refute_operator.md b/changelog/fix_error_for_minitest_assert_operator_and_refute_operator.md
new file mode 100644
index 00000000..a890e1df
--- /dev/null
+++ b/changelog/fix_error_for_minitest_assert_operator_and_refute_operator.md
@@ -0,0 +1 @@
+* [#275](https://github.com/rubocop/rubocop-minitest/pull/275): Make `Minitest/AssertMatch` aware of `assert_operator` when running with Ruby 2.7. ([@koic][])
diff --git a/lib/rubocop/cop/minitest/assert_operator.rb b/lib/rubocop/cop/minitest/assert_operator.rb
index 241adca2..15b2935a 100644
--- a/lib/rubocop/cop/minitest/assert_operator.rb
+++ b/lib/rubocop/cop/minitest/assert_operator.rb
@@ -40,7 +40,7 @@ def on_send(node)
 
         def build_new_arguments(node)
           lhs, op, rhs = *node.first_argument
-          new_arguments = "#{lhs.source}, :#{op}, #{rhs.source}"
+          new_arguments = +"#{lhs.source}, :#{op}, #{rhs.source}"
 
           if node.arguments.count == 2
             new_arguments << ", #{node.last_argument.source}"
diff --git a/lib/rubocop/cop/minitest/refute_operator.rb b/lib/rubocop/cop/minitest/refute_operator.rb
index 213ebeeb..be58bd8c 100644
--- a/lib/rubocop/cop/minitest/refute_operator.rb
+++ b/lib/rubocop/cop/minitest/refute_operator.rb
@@ -40,7 +40,7 @@ def on_send(node)
 
         def build_new_arguments(node)
           lhs, op, rhs = *node.first_argument
-          new_arguments = "#{lhs.source}, :#{op}, #{rhs.source}"
+          new_arguments = +"#{lhs.source}, :#{op}, #{rhs.source}"
 
           if node.arguments.count == 2
             new_arguments << ", #{node.last_argument.source}"