Create SearchLogger model

Why are these changes being introduced:

* This will simplify logic in GraphQL while making it easier to expand
  the logic necessary to add more complex logic to preprocess terms for
  each source or do any other normalization to incoming data.

Relevant ticket(s):

* Pre-work for: https://mitlibraries.atlassian.net/browse/TCO-113

app/graphql/types/query_type.rb

@@ -38,9 +38,7 @@ def nodes(ids:)
     end
 
     def log_search_event(search_term:, source_system:)
-      term = Term.create_or_find_by!(phrase: search_term)
-      term.calculate_categorizations
-      term.search_events.create!(source: source_system)
+      SearchLogger.logevent(search_term, source_system)
     end
 
     def lookup_term(search_term:)

app/models/search_logger.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+# SearchLogger handles logging of search events including coordination of any preprocessing or normalization
+# of data.
+class SearchLogger
+  # Receives a phrase and source and creates a search event. Will find or create a term as needed.
+  # @return [SearchEvent] the newly created SearchEvent
+  def self.logevent(phrase, source)
+    term = Term.create_or_find_by!(phrase:)
+    term.calculate_categorizations
+    term.search_events.create!(source:)
+  end
+end

test/models/search_logger_test.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+#
+require 'test_helper'
+
+class SearchLoggerTest < ActiveSupport::TestCase
+  test 'a term is created if it does not exist' do
+    orig_term_count = Term.count
+    phrase = 'a term is created if it does not exist'
+    SearchLogger.logevent(phrase, 'search logger test')
+
+    assert_operator(Term.count, :>, orig_term_count)
+  end
+
+  test 'a term is not created if it already exists' do
+    orig_term_count = Term.count
+    phrase = Term.first.phrase
+    SearchLogger.logevent(phrase, 'search logger test')
+
+    assert_equal(orig_term_count, Term.count)
+  end
+
+  test 'a new search event is created for an existing term' do
+    orig_searchevent_count = SearchEvent.count
+    phrase = Term.first.phrase
+    SearchLogger.logevent(phrase, 'search logger test')
+
+    assert_equal(orig_searchevent_count + 1, SearchEvent.count)
+  end
+
+  test 'a new search event is created for a new term' do
+    orig_searchevent_count = SearchEvent.count
+    phrase = 'a new search event is created for a new term'
+    SearchLogger.logevent(phrase, 'search logger test')
+
+    assert_equal(orig_searchevent_count + 1, SearchEvent.count)
+  end
+end