Add function for updating problem count

app/models/problem.rb

@@ -15,4 +15,13 @@ class Problem < ActiveRecord::Base
   def original_url
     "https://projecteuler.net/problem=#{self.id}"
   end
+
+  def self.update_count(new_count)
+    old_count = Problem.count
+    raise ArgumentError, "new count has to be larger than old count" if new_count < old_count
+
+    new_count.times do |i|
+      Problem.where(id: i + 1).first_or_create!
+    end
+  end
 end

test/models/problem_test.rb

@@ -17,4 +17,21 @@ class ProblemTest < ActiveSupport::TestCase
   test "should have correct original url" do
     assert_equal "https://projecteuler.net/problem=1", problems(:one).original_url
   end
+
+  test "should allow for problem count updating" do
+    Problem.update_count(10)
+    assert_not Problem.where(id: 0).exists?
+    (1..10).each do |i|
+      assert Problem.where(id: i).exists?
+    end
+    assert_equal "First title", Problem.find(1).title
+  end
+
+  test "should not allow decreasing problem count update" do
+
+    assert_raises ArgumentError do
+      Problem.update_count(1)
+    end
+    assert_equal 3, Problem.count()
+  end
 end