3 files changed, 12 insertions, 5 deletions
diff --git a/activesupport/lib/active_support/core_ext/integer/multiple.rb b/activesupport/lib/active_support/core_ext/integer/multiple.rb
index e7606662d3..bd57a909c5 100644
--- a/activesupport/lib/active_support/core_ext/integer/multiple.rb
+++ b/activesupport/lib/active_support/core_ext/integer/multiple.rb
@@ -7,6 +7,6 @@ class Integer
   #   6.multiple_of?(5)  # => false
   #   10.multiple_of?(2) # => true
   def multiple_of?(number)
-    number != 0 ? self % number == 0 : zero?
+    number == 0 ? self == 0 : self % number == 0
   end
 end
diff --git a/activesupport/lib/active_support/tagged_logging.rb b/activesupport/lib/active_support/tagged_logging.rb
index b069ac94d4..dd72da500c 100644
--- a/activesupport/lib/active_support/tagged_logging.rb
+++ b/activesupport/lib/active_support/tagged_logging.rb
@@ -61,8 +61,15 @@ module ActiveSupport
     end
 
     def self.new(logger)
-      # Ensure we set a default formatter so we aren't extending nil!
-      logger.formatter ||= ActiveSupport::Logger::SimpleFormatter.new
+      logger = logger.dup
+
+      if logger.formatter
+        logger.formatter = logger.formatter.dup
+      else
+        # Ensure we set a default formatter so we aren't extending nil!
+        logger.formatter = ActiveSupport::Logger::SimpleFormatter.new
+      end
+
       logger.formatter.extend Formatter
       logger.extend(self)
     end
diff --git a/activesupport/lib/active_support/test_case.rb b/activesupport/lib/active_support/test_case.rb
index f17743b6db..ef12c6b9b0 100644
--- a/activesupport/lib/active_support/test_case.rb
+++ b/activesupport/lib/active_support/test_case.rb
@@ -65,8 +65,8 @@ module ActiveSupport
       #
       #   parallelize(workers: 2, with: :threads)
       #
-      # The threaded parallelization uses Minitest's parallel executor directly.
-      # The processes parallelization uses a Ruby Drb server.
+      # The threaded parallelization uses minitest's parallel executor directly.
+      # The processes parallelization uses a Ruby DRb server.
       def parallelize(workers: 2, with: :processes)
         workers = ENV["PARALLEL_WORKERS"].to_i if ENV["PARALLEL_WORKERS"]