formula_desc_cop_spec: add whitespace tests

Library/Homebrew/test/rubocops/formula_desc_cop_spec.rb

@@ -101,6 +101,26 @@ describe RuboCop::Cop::FormulaAuditStrict::Desc do
       RUBY
     end
 
+    it "When the description starts with a leading space" do
+      expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+        class Foo < Formula
+          url 'http://example.com/foo-1.0.tgz'
+          desc ' Description with a leading space'
+                ^ Description shouldn\'t have a leading space
+        end
+      RUBY
+    end
+
+    it "When the description ends with a trailing space" do
+      expect_offense(<<~RUBY, "/homebrew-core/Formula/foo.rb")
+        class Foo < Formula
+          url 'http://example.com/foo-1.0.tgz'
+          desc 'Description with a trailing space '
+                                                 ^ Description shouldn\'t have a trailing space
+        end
+      RUBY
+    end
+
     it "autocorrects all rules" do
       source = <<~RUBY
         class Foo < Formula