Remove the json_schema dependency

We do not want to include the json_schema as a dependency of the gem, since the
idea is to the json_schema to be used only by the test helper.

This patch load the json_schema only inside the `assert_response_schema` test
helper and raises a good error message when the the json_schema gem is not
installed.

active_model_serializers.gemspec

@@ -46,8 +46,6 @@ Gem::Specification.new do |spec|
     # activesupport
     # activemodel
 
-  spec.add_runtime_dependency 'json_schema'
-
   # Soft dependency for pagination
   spec.add_development_dependency 'kaminari', ' ~> 0.16.3'
   spec.add_development_dependency 'will_paginate', '~> 3.0', '>= 3.0.7'
@@ -56,4 +54,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'timecop', '~> 0.7'
   spec.add_development_dependency 'minitest-reporters'
   spec.add_development_dependency 'grape', ['>= 0.13', '< 1.0']
+  spec.add_development_dependency 'json_schema'
 end

docs/howto/test.md

@@ -1,5 +1,11 @@
 # How to test
 
+## Dependencies
+
+To use the `assert_response_schema` you need to have the
+[`json_schema`](https://github.com/brandur/json_schema) on your Gemfile. Please
+add it to your Gemfile and run `$ bundle install`.
+
 ## Minitest test helpers
 
 ActiveModelSerializers provides a `assert_response_schema` method to be used on your controller tests to

lib/active_model_serializers/test/schema.rb

@@ -1,5 +1,3 @@
-require 'json_schema'
-
 module ActiveModelSerializers
   module Test
     module Schema
@@ -23,6 +21,7 @@ class AssertResponseSchema
         attr_reader :schema_path, :response, :message
 
         def initialize(schema_path, response, message)
+          require_json_schema!
           @response = response
           @schema_path = schema_path || schema_path_default
           @message = message
@@ -92,6 +91,12 @@ def load_json_file(path)
         rescue Errno::ENOENT
           raise MissingSchema, "No Schema file at #{schema_full_path}"
         end
+
+        def require_json_schema!
+          require 'json_schema'
+        rescue LoadError
+          raise LoadError, "You don't have json_schema installed in your application. Please add it to your Gemfile and run bundle install"
+        end
       end
     end
   end