add tests

test/models/supported_language_test.rb

@@ -1,7 +1,14 @@
 require "test_helper"
 
 class SupportedLanguageTest < ActiveSupport::TestCase
-  # test "the truth" do
-  #   assert true
-  # end
+  test "should be valid with all attributes" do
+    language = SupportedLanguage.new(code: "es", name: "Spanish", native_name: "Español")
+    assert language.valid?
+  end
+
+  test "should be invalid with a duplicate code" do
+    SupportedLanguage.create(code: "de", name: "German", native_name: "Deutsch")
+    language = SupportedLanguage.new(code: "de", name: "German", native_name: "Deutsch")
+    assert_not language.valid?
+  end
 end