create spec/models/comment_spec and add a few tests for children count

spec/models/comment_spec.rb

@@ -0,0 +1,41 @@
+require 'rails_helper'
+
+describe Comment do
+
+  let(:comment) { build(:comment) }
+
+  it "should be valid" do
+    expect(comment).to be_valid
+  end
+
+  describe "#children_count" do
+    let(:comment) { create(:comment) }
+    let(:debate)  { comment.debate }
+
+    it "should count first level children" do
+      parent = comment
+
+      3.times do
+        create(:comment, commentable: debate).
+        move_to_child_of(parent)
+        parent = parent.children.first
+      end
+
+      expect(comment.children_count).to eq(1)
+      expect(debate.comment_threads.count).to eq(4)
+    end
+
+    it "should increase children count" do
+      expect do
+        create(:comment, commentable: debate).
+        move_to_child_of(comment)
+      end.to change { comment.children_count }.from(0).to(1)
+    end
+
+    it "should decrease children count" do
+      new_comment = create(:comment, commentable: debate).move_to_child_of(comment)
+
+      expect { new_comment.destroy }.to change { comment.children_count }.from(1).to(0)
+    end
+  end
+end