Macro that creates a test asserting a change between the return value of a block that is run before and after the current setup block is run. This is similar to Active Support‘s assert_difference assertion, but supports more than just numeric values. See also should_not_change.

The passed description will be used when generating the test name and failure messages.

Example:

  context "Creating a post" do
    setup { Post.create }
    should_change("the number of posts", :by => 1) { Post.count }
  end

As shown in this example, the :by option expects a numeric difference between the before and after values of the expression. You may also specify :from and :to options:

  should_change("the number of posts", :from => 0, :to => 1) { Post.count }
  should_change("the post title", :from => "old", :to => "new") { @post.title }

Combinations of :by, :from, and :to are allowed:

  # Assert the value changed in some way:
  should_change("the post title") { @post.title }

  # Assert the value changed to anything other than "old:"
  should_change("the post title", :from => "old") { @post.title }

  # Assert the value changed to "new:"
  should_change("the post title", :to => "new") { @post.title }

Macro that creates a test asserting that a record of the given class was created.

Example:

  context "creating a post" do
    setup { Post.create(post_attributes) }
    should_create :post
  end

Macro that creates a test asserting that a record of the given class was destroyed.

Example:

  context "destroying a post" do
    setup { Post.first.destroy }
    should_destroy :post
  end

Macro that creates a test asserting no change between the return value of a block that is run before and after the current setup block is run. This is the logical opposite of should_change.

The passed description will be used when generating the test name and failure message.

Example:

  context "Updating a post" do
    setup { @post.update_attributes(:title => "new") }
    should_not_change("the number of posts") { Post.count }
  end