Fix a false negative for RSpec/ExcessiveDocstringSpacing when finds description with em space

This PR is fix a false negative for `RSpec/ExcessiveDocstringSpacing` when finds description with em space.

The motivation for this PR is to be able to detect and autocorrect the em space
that are sometimes left behind because they cannot be detected by
the current `RSpec/ExcessiveDocstringSpacing`.

Author: ydah

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Master (Unreleased)
 
+- Fix a false negative for `RSpec/ExcessiveDocstringSpacing` when finds description with em space. ([@ydah])
+
 ## 2.22.0 (2023-05-06)
 
 - Extract factory_bot cops to a separate repository, [`rubocop-factory_bot`](https://github.com/rubocop/rubocop-factory_bot). The `rubocop-factory_bot` repository is a dependency of `rubocop-rspec` and the factory_bot cops are aliased (`RSpec/FactoryBot/Foo` == `FactoryBot/Foo`) until v3.0 is released, so the change will be invisible to users until then. ([@ydah])

lib/rubocop/cop/rspec/excessive_docstring_spacing.rb

@@ -52,14 +52,21 @@ def on_send(node)
 
         # @param text [String]
         def excessive_whitespace?(text)
-          return true if text.start_with?(' ') || text.end_with?(' ')
-
-          text.match?(/[^\n ]  +[^ ]/)
+          text.match?(/
+            # Leading space
+            \A[[:blank:]]
+            |
+            # Trailing space
+            [[:blank:]]\z
+            |
+            # Two or more consecutive spaces, except if they are leading spaces
+            [^[[:space:]]][[:blank:]]{2,}[^[[:blank:]]]
+          /x)
         end
 
         # @param text [String]
         def strip_excessive_whitespace(text)
-          text.strip.gsub(/  +/, ' ')
+          text.strip.gsub(/[[:blank:]]{2,}/, ' ')
         end
 
         # @param node [RuboCop::AST::Node]

spec/rubocop/cop/rspec/excessive_docstring_spacing_spec.rb

@@ -26,6 +26,19 @@
       RUBY
     end
 
+    it 'finds description with leading em space' do
+      expect_offense(<<-RUBY)
+        describe '　　#mymethod' do
+                  ^^^^^^^^^^^ Excessive whitespace.
+        end
+      RUBY
+
+      expect_correction(<<-RUBY)
+        describe '#mymethod' do
+        end
+      RUBY
+    end
+
     it 'finds interpolated description with leading whitespace' do
       expect_offense(<<-'RUBY')
         describe "  ##{:stuff}" do
@@ -52,6 +65,19 @@
       RUBY
     end
 
+    it 'finds description with trailing em space' do
+      expect_offense(<<-RUBY)
+        describe '#mymethod　　' do
+                  ^^^^^^^^^^^ Excessive whitespace.
+        end
+      RUBY
+
+      expect_correction(<<-RUBY)
+        describe '#mymethod' do
+        end
+      RUBY
+    end
+
     it 'finds interpolated description with trailing whitespace' do
       expect_offense(<<-'RUBY')
         describe "##{:stuff}  " do