Fix run_via[]= backwards compatibility.

```
Minitest.run_via[:rails] = true
```

👆 would break because a simple alias won't catch the second
true argument there.

2 files changed, 13 insertions, 1 deletions

diff --git a/railties/lib/rails/test_unit/minitest_plugin.rb b/railties/lib/rails/test_unit/minitest_plugin.rb
index 7d3da6b529..e44fe78bbd 100644
--- a/railties/lib/rails/test_unit/minitest_plugin.rb
+++ b/railties/lib/rails/test_unit/minitest_plugin.rb
@@ -115,7 +115,9 @@ module Minitest
     alias set? runner
 
     # Backwardscompatibility with Rails 5.0 generated plugin test scripts.
-    alias []= runner=
+    def []=(runner, *)
+      @runner = runner
+    end
 
     def ruby?
       runner == :ruby
diff --git a/railties/test/application/test_runner_test.rb b/railties/test/application/test_runner_test.rb
index d3d5b6d6dd..ee03d8b86c 100644
--- a/railties/test/application/test_runner_test.rb
+++ b/railties/test/application/test_runner_test.rb
@@ -15,6 +15,16 @@ module ApplicationTests
       teardown_app
     end
 
+    def test_run_via_backwardscompatibility
+      require "rails/test_unit/minitest_plugin"
+
+      assert_nothing_raised do
+        Minitest.run_via[:ruby] = true
+      end
+
+      assert_predicate Minitest.run_via, :ruby?
+    end
+
     def test_run_single_file
       create_test_file :models, "foo"
       create_test_file :models, "bar"