Improve spec branch coverage for ConfigFormatter

AMENDMENTS was defined as a String, not an Array. And splatting the
array into `#gsub` doesn't work if there is more than one element - we
would need to use `Regexp.union` instead...

but actually I ended up removing AMENDMENTS altogether. All we want to
do is to add an extra newline before each cop entry. Only new cop
entries starts at the beginning of line, and contains a slash character
after the first word. This means we don't need AMENDMENTS at all, and we
no longer need the capture in EXTENSION_ROOT_DEPARTMENT.

Author: bquorning

lib/rubocop/rspec/config_formatter.rb

@@ -6,8 +6,7 @@ module RuboCop
   module RSpec
     # Builds a YAML config file from two config hashes
     class ConfigFormatter
-      EXTENSION_ROOT_DEPARTMENT = %r{^(RSpec/)}.freeze
-      AMENDMENTS = %(Metrics/BlockLength)
+      EXTENSION_ROOT_DEPARTMENT = %r{^RSpec/}.freeze
       COP_DOC_BASE_URL = 'https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/'
 
       def initialize(config, descriptions)
@@ -17,8 +16,7 @@ def initialize(config, descriptions)
 
       def dump
         YAML.dump(unified_config)
-          .gsub(EXTENSION_ROOT_DEPARTMENT, "\n\\1")
-          .gsub(*AMENDMENTS, "\n\\0")
+          .gsub(%r{^\w+/}, "\n\\0")
           .gsub(/^(\s+)- /, '\1  - ')
           .gsub('"~"', '~')
       end
@@ -27,8 +25,6 @@ def dump
 
       def unified_config
         cops.each_with_object(config.dup) do |cop, unified|
-          next if AMENDMENTS.include?(cop)
-
           replace_nil(unified[cop])
           unified[cop].merge!(descriptions.fetch(cop))
           unified[cop]['Reference'] = reference(cop)

spec/rubocop/rspec/config_formatter_spec.rb

@@ -8,6 +8,12 @@
       'AllCops' => {
         'Setting' => 'forty two'
       },
+      'Metrics/BlockLength' => {
+        'Exclude' => [
+          '**/*_spec.rb',
+          '**/spec/**/*'
+        ]
+      },
       'RSpec/Foo' => {
         'Config' => 2,
         'Enabled' => true
@@ -18,6 +24,7 @@
       },
       'RSpec/Baz' => {
         'Enabled' => true,
+        'NegatedMatcher' => '~',
         'StyleGuide' => '#buzz'
       }
     }
@@ -45,6 +52,11 @@
       AllCops:
         Setting: forty two
 
+      Metrics/BlockLength:
+        Exclude:
+          - "**/*_spec.rb"
+          - "**/spec/**/*"
+
       RSpec/Foo:
         Config: 2
         Enabled: true
@@ -59,6 +71,7 @@
 
       RSpec/Baz:
         Enabled: true
+        NegatedMatcher: ~
         StyleGuide: "#buzz"
         Description: Woof
         Reference: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/Baz