Fix edge cases with automated CHANGELOG

Handle the case when no blank line is present after an existing header: it
  will add one

Signed-off-by: Rémy Coutable <remy@rymai.me>

lib/changelog/updater.rb

@@ -45,12 +45,21 @@ module Changelog
           header = Version.new($1)
           if version.to_ce == header
+            no_blank_line_below_header = contents[index + 1].chomp != ''
             entries = markdown.lines
-            entries.shift(2) # Remove the header and the blank line
-            entries.pop      # Remove the trailing blank line
+            entries.shift # Remove the header
+            entries.shift unless no_blank_line_below_header # Remove the blank line if present
+            entries.pop   # Remove the trailing blank line
             # Insert the entries below the existing header and its blank line
-            contents.insert(index + 2, entries)
+            insert_at =
+              if no_blank_line_below_header
+                index + 1
+              else
+                index + 2
+              end
+
+            contents.insert(insert_at, entries)
             break
           elsif version.major >= header.major && version.minor >= header.minor
             contents.insert(index, *markdown.lines)

spec/fixtures/changelog/CHANGELOG.md

@@ -53,7 +53,6 @@
 - Change I
 ## 8.8.7 (2016-07-04)
-
 - Change A
 ## 8.8.6 (2016-06-28)

spec/lib/changelog/updater_spec.rb

@@ -64,6 +64,23 @@ describe Changelog::Updater do
         - Change A
       MD
     end
+
+    it 'correctly inserts entries for a pre-existing version header without a blank line' do
+      version = Version.new('8.8.7-ee')
+      markdown = markdown(version)
+
+      writer = described_class.new(contents, version)
+      contents = writer.insert(markdown)
+
+      expect(contents).to include(<<-MD.strip_heredoc)
+        ## 8.8.7 (2016-07-04)
+
+        - Change Z
+        - Change Y
+        - Change X
+        - Change A
+      MD
+    end
   end
   def markdown(version)