Fix mixing line filters with Minitest's -n filter.

Previous commit accidentally broke mixing line filters with string -n filter.

Fix by checking if it is a string and returning it.

We also need to ensure the -n filter carry forward into any other composite filters.

Fix by letting the named filter be extractable, so we'll keep this for the next runnable's
run.

railties/lib/rails/test_unit/line_filtering.rb

@@ -13,9 +13,12 @@ def run(reporter, options = {})
   end
 
   class CompositeFilter # :nodoc:
+    attr_reader :named_filter
+
     def initialize(runnable, filter, patterns)
       @runnable = runnable
-      @filters = [ derive_regexp(filter), *derive_line_filters(patterns) ].compact
+      @named_filter = derive_named_filter(filter)
+      @filters = [ @named_filter, *derive_line_filters(patterns) ].compact
     end
 
     # Minitest uses === to find matching filters.
@@ -24,9 +27,14 @@ def ===(method)
     end
 
     private
-      def derive_regexp(filter)
-        # Regexp filtering copied from Minitest.
-        Regexp.new $1 if filter =~ %r%/(.*)/%
+      def derive_named_filter(filter)
+        if filter.respond_to?(:named_filter)
+          filter.named_filter
+        elsif filter =~ %r%/(.*)/% # Regexp filtering copied from Minitest.
+          Regexp.new $1
+        elsif filter.is_a?(String)
+          filter
+        end
       end
 
       def derive_line_filters(patterns)

railties/test/application/test_runner_test.rb

@@ -406,6 +406,30 @@ class SecondPostTest < ActiveSupport::TestCase
       end
     end
 
+    def test_line_filter_with_minitest_string_filter
+      app_file 'test/models/post_test.rb', <<-RUBY
+        require 'test_helper'
+
+        class PostTest < ActiveSupport::TestCase
+          test 'by line' do
+            puts 'by line'
+            assert true
+          end
+
+          test 'by name' do
+            puts 'by name'
+            assert true
+          end
+        end
+      RUBY
+
+      run_test_command('test/models/post_test.rb:4 -n test_by_name').tap do |output|
+        assert_match 'by line', output
+        assert_match 'by name', output
+        assert_match '2 runs, 2 assertions', output
+      end
+    end
+
     def test_shows_filtered_backtrace_by_default
       create_backtrace_test