Asserting the number of database queries or cache lookups performed for tests

assert_database_queries_example.rb

require 'path/to/test_helper'

class ExampleTest
  test 'this should trigger 1 database query' do
    assert_db_queries(1) do
      # ... code
    end
  end
end

count_database_and_cache_queries.rb

class TestHelper  
  # Count SQL queries
  # [optional] 
    # We record the actual queries, and print them out if the assertion fails. 
    # It enables us to see what extra queries we are invoking. Helps a lot with debugging.
  def assert_db_queries(expected_hits, debug: false, &block)
    actual_hits = 0
    queries = []

    counter_f = ->(_name, _started, _finished, _unique_id, payload) do
      unless payload[:name].in? %w[CACHE SCHEMA]
        queries << payload[:sql]
        actual_hits += 1
      end
    end

    ActiveSupport::Notifications.subscribed(counter_f, 'sql.active_record', &block)

    actual_queries = "Queries performed:\n#{queries.join("\n")}"
    puts actual_queries if debug
    assert_equal expected_hits, actual_hits, actual_queries
  end

  def assert_cache_queries(expected_hits, debug: false, &block)
    actual_hits = 0
    queries = []

    counter_f = ->(_name, _started, _finished, _unique_id, payload) do
      if payload[:hit]
        queries << payload[:key]
        actual_hits += 1
      end
    end

    ActiveSupport::Notifications.subscribed(counter_f, 'cache_read.active_support', &block)

    actual_queries = "Queries performed:\n#{queries.join("\n")}"
    puts actual_queries if debug
    assert_equal expected_hits, actual_hits, actual_queries
  end
end