Respect extra_failure_lines in RSpec metadata

RSpec tests can have associated metadata, which is just a hash of
content. One magic metadata property is `extra_failure_lines`. If this
property is set, then RSpec will read its content and include it in the
output it prints if the test fails.

This property particularly comes into play in RSpec system specs, a
wrapper around Rails system tests. If a system test fails, a screenshot
is automatically taken of the page (provided the driver supports it) and
a message is printed which details the path to the screenshot. RSpec's
wrapper will capture output generated while the test is running and then
store it in `extra_failure_lines`. By doing this, output (including the
screenshot path, but potentially other information as well) is
effectively moved to the spec failure message.

This gem, as it patches key parts of `rspec-rails`, doesn't support
`extra_failure_lines`, so anything in this metadata property is
effectively discarded. This commit restores support.

Co-authored-by: willnet <netwillnet@gmail.com>

Author: willnet

lib/super_diff/rspec/monkey_patches.rb

@@ -218,7 +218,10 @@ def failure_line_groups
                   }
                 end
               end
-
+              @failure_line_groups << {
+                lines: extra_failure_lines,
+                already_colorized: true
+              }
               @failure_line_groups
             end
           end
@@ -241,6 +244,24 @@ def failure_slash_error_lines
             lines
           end
 
+          # Override to ensure that each item in the array returned is one and
+          # only one line and doesn't contain any newline characters
+          def extra_failure_lines
+            @extra_failure_lines ||=
+              begin
+                original_lines = Array(example.metadata[:extra_failure_lines])
+                normalized_lines =
+                  original_lines.flat_map { |line| line.split("\n") }
+                unless normalized_lines.empty?
+                  unless normalized_lines.first == ""
+                    normalized_lines.unshift("")
+                  end
+                  normalized_lines.push("") unless normalized_lines.last == ""
+                end
+                normalized_lines
+              end
+          end
+
           # Exclude this file from being included in backtraces, so that the
           # SnippetExtractor prints the right thing
           def find_failed_line

spec/integration/rspec/magic_metadata_spec.rb

@@ -0,0 +1,51 @@
+require "spec_helper"
+
+RSpec.describe "Integration with RSpec's magic metadata", type: :integration do
+  it "includes extra_failure_lines in failure messages" do
+    as_both_colored_and_uncolored do |color_enabled|
+      snippet = <<~TEST.strip
+          RSpec.describe "test" do
+            it { expect(true).to be(false) }
+
+            after do
+              RSpec.current_example.metadata[:extra_failure_lines] = "foo\nbar"
+            end
+          end
+        TEST
+      program =
+        make_plain_test_program(
+          snippet,
+          color_enabled: color_enabled,
+          preserve_as_whole_file: true
+        )
+
+      expected_output =
+        build_expected_output(
+          color_enabled: color_enabled,
+          test_name: "test is expected to equal false",
+          snippet: "it { expect(true).to be(false) }",
+          expectation:
+            proc do
+              line do
+                plain "Expected "
+                actual "true"
+                plain " to equal "
+                expected "false"
+                plain "."
+              end
+            end,
+          extra_failure_lines:
+            proc do
+              indent by: 5 do
+                line "foo"
+                line "bar"
+              end
+            end
+        )
+
+      expect(program).to produce_output_when_run(expected_output).in_color(
+        color_enabled
+      )
+    end
+  end
+end

spec/support/integration/helpers.rb

@@ -48,15 +48,17 @@ def build_expected_output(
       color_enabled:,
       snippet:,
       expectation:,
+      test_name: "test passes",
       key_enabled: true,
       newline_before_expectation: false,
       indentation: 7,
-      diff: nil
+      diff: nil,
+      extra_failure_lines: nil
     )
       colored(color_enabled: color_enabled) do
         line "Failures:\n"
 
-        line "1) test passes", indent_by: 2
+        line "1) #{test_name}", indent_by: 2
 
         line indent_by: 5 do
           bold "Failure/Error: "
@@ -106,6 +108,11 @@ def build_expected_output(
             newline
           end
         end
+
+        if extra_failure_lines
+          newline
+          evaluate_block(&extra_failure_lines)
+        end
       end
     end