FIX: Show a correct diff when editing consecutive paragraphs (#8177)

spec/components/discourse_diff_spec.rb

@@ -76,6 +76,13 @@ describe DiscourseDiff do
       expect(DiscourseDiff.new(before, after).side_by_side_html).to eq("<div class=\"revision-content\"><p>this is a paragraph</p></div><div class=\"revision-content\"><p>this is a <ins>great </ins>paragraph</p></div>")
     end
 
+    it "adds <ins> and <del> tags on consecutive paragraphs", :focus do
+      before = "<p>this is one paragraph</p><p>here is yet another</p>"
+      after = "<p>this is one great paragraph</p><p>here is another</p>"
+      got = DiscourseDiff.new(before, after).side_by_side_html
+      expect(got).to eq("<div class=\"revision-content\"><p>this is one paragraph</p><p>here is <del>yet </del>another</p></div><div class=\"revision-content\"><p>this is one <ins>great </ins>paragraph</p><p>here is another</p></div>")
+    end
+
     it "adds <del> tags around removed text on the left div" do
       before = "<p>this is a great paragraph</p>"
       after = "<p>this is a paragraph</p>"

spec/components/onpdiff_spec.rb

@@ -39,4 +39,38 @@ describe ONPDiff do
 
   end
 
+  describe "paragraph_diff" do
+
+    it "returns an empty array when there is no content to diff" do
+      expect(ONPDiff.new("", "").paragraph_diff).to eq([])
+    end
+
+    it "returns an array with the operation code for each element" do
+      expect(ONPDiff.new("abc", "acd").paragraph_diff).to eq([["a", :common], ["b", :delete], ["c", :common], ["d", :add]])
+    end
+
+    it "pairs as many elements as possible", :focus do
+      expect(ONPDiff.new("abcd", "abef").paragraph_diff).to eq([
+        ["a", :common], ["b", :common],
+        ["e", :add], ["c", :delete],
+        ["f", :add], ["d", :delete]
+      ])
+
+      expect(ONPDiff.new("abcde", "abfg").paragraph_diff).to eq([
+        ["a", :common], ["b", :common],
+        ["c", :delete],
+        ["d", :delete], ["f", :add],
+        ["e", :delete], ["g", :add]
+      ])
+
+      expect(ONPDiff.new("abcd", "abefg").paragraph_diff).to eq([
+        ["a", :common], ["b", :common],
+        ["e", :add],
+        ["f", :add], ["c", :delete],
+        ["g", :add], ["d", :delete]
+      ])
+    end
+
+  end
+
 end