Configurable warning behaviour

lib/rspec/core/configuration.rb

@@ -1421,6 +1421,25 @@ def warnings?
         $VERBOSE
       end
 
+      # @private
+      RAISE_ERROR_WARNING_NOTIFIER = lambda { |message| raise message }
+
+      # Turns warnings into errors. This can be useful when
+      # you want RSpec to run in a 'strict' no warning situation.
+      #
+      # @example
+      #
+      #   RSpec.configure do |rspec|
+      #     rspec.raise_on_warning = true
+      #   end
+      def raise_on_warning=(value)
+        if value
+          RSpec::Support.warning_notifier = RAISE_ERROR_WARNING_NOTIFIER
+        else
+          RSpec::Support.warning_notifier = RSpec::Support::DEFAULT_WARNING_NOTIFIER
+        end
+      end
+
       # Exposes the current running example via the named
       # helper method. RSpec 2.x exposed this via `example`,
       # but in RSpec 3.0, the example is instead exposed via

spec/rspec/core/configuration_spec.rb

@@ -1963,6 +1963,27 @@ def strategy.order(list)
       end
     end
 
+    describe '#raise_on_warning=(value)' do
+      around do |example|
+        original_setting = RSpec::Support.warning_notifier
+        example.run
+        RSpec::Support.warning_notifier = original_setting
+      end
+
+      it 'causes warnings to raise errors when true' do
+        config.raise_on_warning = true
+        expect {
+          RSpec.warning 'All hell breaks loose'
+        }.to raise_error a_string_including('WARNING: All hell breaks loose')
+      end
+
+      it 'causes warnings to default to warning when false' do
+        config.raise_on_warning = false
+        expect_warning_with_call_site(__FILE__, __LINE__ + 1)
+        RSpec.warning 'doesnt raise'
+      end
+    end
+
     describe "#raise_errors_for_deprecations!" do
       it 'causes deprecations to raise errors rather than printing to the deprecation stream' do
         config.deprecation_stream = stream = StringIO.new