ruby script/plugin install svn://rubyforge.org/var/svn/migrationtest/tags/migration_test_helper

assert_schema: verifies the schema of the database exactly matches the one specified.

  def test_the_schema
    assert_schema do |s|
      s.table :books do |t|
        t.column :id,     :integer
        t.column :title,  :string, :limit => 5
        t.column :author, :string
      end

      s.table :reviews do |t|
        t.column :id,      :integer
        t.column :book_id, :integer
        t.column :body,    :text
        t.column :rating,  :integer, :default => 0
      end
    end
  end

This would verify there are only two tables defined in the test database: books and reviews (schema_info is ignored). It will also verify that the book table has the three columns, id, title and author, each with their respective types.

assert_table: verify a table is found exactly as specified:

  assert_table :books do |t|
    t.column :id,     :integer
    t.column :title,  :string, :limit => 5
    t.column :author, :string
  end

drop_all_tables: does just what it says to your test database.

migrate: executes the migrations against the test database using the same mechanism as rake db:migrate.

  def test_the_migrations
    migrate
    migrate :version => 0
    migrate :version => 10
    migrate
  end

This would do the same thing as running the following rake commands, but within a test case:

  rake db:migrate
  rake db:migrate VERSION=0
  rake db:migrate VERSION=10
  rake db:migrate

By combining the two helpers you can write a test that shows you can run all your migrations and get the final schema:

  def test_should_be_able_to_migrate_from_an_empty_schema
    drop_all_tables

    # we shouldn't have any tables
    assert_schema do |s|
    end

    migrate

    assert_schema do |s|
      s.table :books do |t|
        t.column :id,     :integer
        t.column :title,  :string
        t.column :author, :string
      end

      s.table :reviews do |t|
        t.column :id,      :integer
        t.column :book_id, :integer
        t.column :body,    :text
        t.column :rating,  :integer
      end
    end
  end

The migrate helper can also be useful for testing data tranformation migrations:

  def test_should_get_rid_of_bad_data
    drop_all_tables
    migrate :version => 7
    Book.reset_column_information
    book = Book.create! :title => "bad title\nwith\todd    spacing"
    migrate :version => 8 # should cleanse spacing in book titles
    book.reload
    assert_equal "bad title with odd spacing", book.title
  end

There is currently no advanced documentation for this plugin.