display nested exception causes

lib/rspec/core/formatters/exception_presenter.rb

@@ -32,12 +32,12 @@ def colorized_message_lines(colorizer=::RSpec::Core::Formatters::ConsoleCodes)
         end
 
         def formatted_backtrace
-          backtrace_formatter.format_backtrace(exception_backtrace, example.metadata)
+          backtrace_formatter.format_backtrace(backtrace_presenter.backtrace, example.metadata)
         end
 
         def colorized_formatted_backtrace(colorizer=::RSpec::Core::Formatters::ConsoleCodes)
           formatted_backtrace.map do |backtrace_info|
-            colorizer.wrap "# #{backtrace_info}", RSpec.configuration.detail_color
+            colorizer.wrap "# #{backtrace_info}".strip, RSpec.configuration.detail_color
           end
         end
 
@@ -54,6 +54,10 @@ def failure_slash_error_line
           @failure_slash_error_line ||= "Failure/Error: #{read_failed_line.strip}"
         end
 
+        def backtrace_presenter
+          @backtrace_presenter ||= BacktracePresenter.new(exception)
+        end
+
       private
 
         def description_and_detail(colorizer, indentation)
@@ -152,6 +156,59 @@ def exception_backtrace
           exception.backtrace || []
         end
 
+        # @private
+        # Format exception backtrace, including nested "cause" exception(s)
+        class BacktracePresenter
+          attr_reader :exception, :nested
+
+          def initialize(exception, nested=false)
+            @exception = exception
+            @nested = nested
+          end
+
+          def backtrace
+            trace = separator
+            trace.concat exception_backtrace
+
+            if exception.respond_to?(:cause)
+              cause = exception.cause
+              if cause
+                trace.concat(BacktracePresenter.new(cause, true).backtrace)
+              end
+            end
+
+            trace
+          end
+
+        private
+
+          def separator
+            if nested
+              ['', '--- Caused by: ---', exception_class_name, exception_message].compact
+            else
+              []
+            end
+          end
+
+          def exception_class_name
+            class_name = exception.class.name.to_s
+            if class_name =~ /RSpec/
+              class_name = nil
+            else
+              class_name << ":"
+            end
+            class_name
+          end
+
+          def exception_message
+            "  #{exception.message}"
+          end
+
+          def exception_backtrace
+            exception.backtrace || []
+          end
+        end
+
         # @private
         # Configuring the `ExceptionPresenter` with the right set of options to handle
         # pending vs failed vs skipped and aggregated (or not) failures is not simple.

spec/rspec/core/formatters/exception_presenter_spec.rb

@@ -121,6 +121,26 @@ module RSpec::Core
           |     extra detail for failure: 2
         EOS
       end
+
+      context 'when cause is set to nested exception' do
+        let(:nested) { instance_double(Exception, :message => "The real problem", :backtrace => ["#{__FILE__}:#{line_num}"], :class => RuntimeError) }
+        let(:exception) { instance_double(Exception, :message => "The top level", :backtrace => ["#{__FILE__}:#{line_num}"], :cause => nested) }
+
+        it 'displays nested exception' do
+          expect(presenter.fully_formatted(2)).to eq(<<-EOS.gsub(/^ +\|/, ''))
+            |
+            |  2) Example
+            |     Failure/Error: # The failure happened here!#{ encoding_check }
+            |       The top level
+            |     # ./spec/rspec/core/formatters/exception_presenter_spec.rb:#{line_num}
+            |     #
+            |     # --- Caused by: ---
+            |     # RuntimeError:
+            |     #   The real problem
+            |     # ./spec/rspec/core/formatters/exception_presenter_spec.rb:#{line_num}
+          EOS
+        end
+      end
     end
 
     describe "#read_failed_line" do