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I often get the question from new rubyist “How should I test my model validations in Rails?”. A simple example is when we have a
Post model with two required fields:
# app/models/post.rb class Post < ActiveRecord::Base validates_presence_of :title, :body end
You could write a test like this:
# test/models/post_test.rb require 'test_helper' class PostTest < ActiveSupport::TestCase test "should not save post without title or body" do post = Post.new assert_not post.save post.title = 'Test' assert_not post.save post.body = 'Test body' assert post.save end end
But this test is already too long and what if you have a lot more required fields? To get around this it is better to test if the validation errors are correct:
# test/models/post_test.rb test "should have the necessary required validators" do post = Post.new assert_not post.valid? assert_equal [:title, :body], post.errors.keys end
Now we cover the existence of the validators with a lot shorter and simpler test.
We can use the same approach to test ther validation rules like
# app/models/post.rb class Post < ActiveRecord::Base validates_presence_of :title, :body validates :score, numericality: true, allow_blank: true end
# test/models/post_test.rb test "should have numeric score" do post = Post.new(title: 'test', body: 'test body', score: 'test') assert_not post.valid? assert_equal ["is not a number"], post.errors.messages[:score] end
And so on.
As some of the readers pointed out if you need a full blown solution with support of
on and etcetera thoughbot’s shoulda-matchers is has all that.