Fix the LoggerSilence to work as described:

- Following the Rails guide which state that a logger needs to include
  the `ActiveSupport::LoggerSilence` as well as
  `ActiveSupport::LoggerThreadSafe` modules isn't enough and won't
  work.

  Here is a test cases with 3 tests that all fails
  https://gist.github.com/Edouard-chin/4a72930c2b1eafbbd72a80c66f102010

  The problems are the following:

  1) The logger needs to call `after_initialize` in order to setup
  some instance variables.
  2) The silence doesn't actually work because the bare ruby Logger
  `add` method checks for the instance variable `@logger`. We need to
  override the `add` (like we used to in the ActiveSupport::Logger
  class).
  3) Calling `debug?` `info?` etc... doesn't work as the bare ruby
  methods will check for the instance variable. Again we need to
  override this methods (like we used to in the ActiveSupport::Logger
  class)

  The LoggerSilence won't work without LoggerThreadSafe, but the later
  is not public API, the user shouldn't have to include it so I
  modified to include it automatically.
  Same for the `after_initialize` method. I find unuintitive to have
  to call it directly. I modified to instance the variables when the
  module get included.

2 files changed, 37 insertions, 1 deletions

diff --git a/activesupport/test/broadcast_logger_test.rb b/activesupport/test/broadcast_logger_test.rb
index ea2e388b8f..02bc317c66 100644
--- a/activesupport/test/broadcast_logger_test.rb
+++ b/activesupport/test/broadcast_logger_test.rb
@@ -123,6 +123,8 @@ module ActiveSupport
     end
 
     class CustomLogger
+      include ActiveSupport::LoggerSilence
+
       attr_reader :adds, :closed, :chevrons
       attr_accessor :level, :progname, :formatter, :local_level
 
@@ -174,7 +176,6 @@ module ActiveSupport
     end
 
     class FakeLogger < CustomLogger
-      include ActiveSupport::LoggerSilence
     end
   end
 end
diff --git a/activesupport/test/silence_logger_test.rb b/activesupport/test/silence_logger_test.rb
new file mode 100644
index 0000000000..fc5c5c1161
--- /dev/null
+++ b/activesupport/test/silence_logger_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/logger_silence"
+require "logger"
+
+class LoggerSilenceTest < ActiveSupport::TestCase
+  class MyLogger < ::Logger
+    include LoggerSilence
+  end
+
+  setup do
+    @io = StringIO.new
+    @logger = MyLogger.new(@io)
+  end
+
+  test "#silence silences the log" do
+    @logger.silence(Logger::ERROR) do
+      @logger.info("Foo")
+    end
+    @io.rewind
+
+    assert_empty @io.read
+  end
+
+  test "#debug? is true when setting the temporary level to Logger::DEBUG" do
+    @logger.level = Logger::INFO
+
+    @logger.silence(Logger::DEBUG) do
+      assert_predicate @logger, :debug?
+    end
+
+    assert_predicate @logger, :info?
+  end
+end