add post count estimates for bulk update requests

test/unit/bulk_update_request_test.rb

@@ -13,6 +13,28 @@ class BulkUpdateRequestTest < ActiveSupport::TestCase
       CurrentUser.ip_addr = nil
     end
 
+    context "#estimate_update_count" do
+      setup do
+        FactoryBot.create(:post, tag_string: "aaa")
+        FactoryBot.create(:post, tag_string: "bbb")
+        FactoryBot.create(:post, tag_string: "ccc")
+        FactoryBot.create(:post, tag_string: "ddd")
+        FactoryBot.create(:post, tag_string: "eee")
+
+        @script = "create alias aaa -> 000\n" +
+          "create implication bbb -> 111\n" +
+          "remove alias ccc -> 222\n" +
+          "remove implication ddd -> 333\n" +
+          "mass update eee -> 444\n"
+      end
+
+      subject { BulkUpdateRequest.new(script: @script) }
+
+      should "return the correct count" do
+        assert_equal(3, subject.estimate_update_count)
+      end
+    end
+
     context "on approval" do
       setup do
         @script = %q(