Add learning tests for countries gem

test/learning/countries_test.rb

@@ -0,0 +1,23 @@
+require 'test_helper'
+
+class CountriesLearningTest < ActiveSupport::TestCase
+  def test_returns_all_countries
+    assert_respond_to Country.all, :sort_by
+  end
+
+  def test_returns_country_name
+    assert_equal 'United States of America', Country.new('US').name
+  end
+
+  def test_returns_country_alpha2_code
+    assert_equal 'US', Country.new('US').alpha2
+  end
+
+  def test_returns_country_alpha3_code
+    assert_equal 'USA', Country.new('US').alpha3
+  end
+
+  def test_validates_code_when_creating_an_instance_of_country
+    assert_not Country.new('invalid')
+  end
+end