Method to add tags to microposts

app/models/micropost.rb

@@ -10,4 +10,10 @@ class Micropost < ApplicationRecord
 
   has_many :microposts_tags
   has_many :tags, through: :microposts_tags
+
+  def add_tags(*tag_names)
+    tag_names.each do |tag|
+      tags << Tag.find_or_create_by(name: tag)
+    end
+  end
 end

test/models/micropost_test.rb

@@ -17,4 +17,11 @@ class MicropostTest < ActiveSupport::TestCase
     @micropost.content = nil
     assert_not @micropost.valid?
   end
+
+  test "can add tags" do
+    assert_empty @micropost.tags
+    assert_difference "@micropost.tags.count", +3 do
+      @micropost.add_tags("foo", "bar", "baz")
+    end
+  end
 end