Tests: enable json tests for MySQL

spec/dummy_app/app/models/fruit.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class Fruit < ActiveRecord::Base
-  if ENV["DB"] == "postgres" || JsonVersion.table_exists?
+  if PaperTrail::TestEnv.json? || JsonVersion.table_exists?
     has_paper_trail versions: { class_name: "JsonVersion" }
   end
 end

spec/dummy_app/db/migrate/20110208155312_set_up_test_tables.rb

@@ -62,7 +62,7 @@ class SetUpTestTables < ::ActiveRecord::Migration::Current
       t.timestamps null: true, limit: 6
     end
 
-    if ENV["DB"] == "postgres"
+    if PaperTrail::TestEnv.json?
       create_table :postgres_users, force: true do |t|
         t.string     :name
         t.integer    :post_ids,    array: true
@@ -127,7 +127,7 @@ class SetUpTestTables < ::ActiveRecord::Migration::Current
     end
     add_index :no_object_versions, %i[item_type item_id]
 
-    if ENV["DB"] == "postgres"
+    if PaperTrail::TestEnv.json?
       create_table :json_versions, force: true do |t|
         t.string   :item_type, null: false
         t.integer  :item_id,   null: false

spec/models/fruit_spec.rb

@@ -2,7 +2,7 @@
 
 require "spec_helper"
 
-if ENV["DB"] == "postgres" || JsonVersion.table_exists?
+if PaperTrail::TestEnv.json? || JsonVersion.table_exists?
   RSpec.describe Fruit, type: :model, versioning: true do
     describe "have_a_version_with_changes matcher" do
       it "works with Fruit because Fruit uses JsonVersion" do

spec/models/version_spec.rb

@@ -114,7 +114,7 @@ module PaperTrail
       # way? We already have a `json_versions` table in our tests, maybe we
       # could use that and add a `jsonb_versions` table?
       column_overrides = [false]
-      if ENV["DB"] == "postgres"
+      if PaperTrail::TestEnv.json?
         column_overrides += %w[json jsonb]
       end
 

spec/paper_trail/attribute_serializers/object_attribute_spec.rb

@@ -5,7 +5,7 @@ require "spec_helper"
 module PaperTrail
   module AttributeSerializers
     ::RSpec.describe ObjectAttribute do
-      if ENV["DB"] == "postgres"
+      if PaperTrail::TestEnv.json?
         describe "postgres-specific column types" do
           describe "#serialize" do
             it "serializes a postgres array into a plain array" do

spec/spec_helper.rb

@@ -3,6 +3,23 @@
 ENV["RAILS_ENV"] ||= "test"
 ENV["DB"] ||= "sqlite"
 
+module PaperTrail
+  module TestEnv
+    # Does the chosen database support json columns?
+    #
+    # - Postgres had json first.
+    # - MySQL added json support in 5.7.
+    # - MariaDB has only partial support, functions but not operators. PT
+    # currently uses operators. The devs consider the addition of operators to
+    # be a low priority feature. (https://jira.mariadb.org/browse/MDEV-13594) PT
+    # may be able to use functions like `json_extract` instead of operators like
+    # `->` but that work has not yet been done. PRs welcome.
+    def self.json?
+      %w[mysql postgres].include?(ENV["DB"])
+    end
+  end
+end
+
 require "byebug"
 require_relative "support/pt_arel_helpers"