Fixtures are a way of organizing data that you want to test against; in short, sample data.
They are stored in YAML files, one file per model, which are placed in the directory appointed by ActiveSupport::TestCase.fixture_path=(path)
(this is automatically configured for Rails, so you can just put your files in <your-rails-app>/test/fixtures/
). The fixture file ends with the .yml
file extension, for example: <your-rails-app>/test/fixtures/web_sites.yml
).
The format of a fixture file looks like this:
rubyonrails:
id: 1
name: Ruby on Rails
url: http://www.rubyonrails.org
google:
id: 2
name: Google
url: http://www.google.com
This fixture file includes two fixtures. Each YAML fixture (i.e. record) is given a name and is followed by an indented list of key/value pairs in the “key: value” format. Records are separated by a blank line for your viewing pleasure.
Note: Fixtures are unordered. If you want ordered fixtures, use the omap YAML type. See yaml.org/type/omap.html for the specification. You will need ordered fixtures when you have foreign key constraints on keys in the same table. This is commonly needed for tree structures. Example:
--- !omap
- parent:
id: 1
parent_id: NULL
title: Parent
- child:
id: 2
parent_id: 1
title: Child
Using Fixtures in Test Cases
Since fixtures are a testing construct, we use them in our unit and functional tests. There are two ways to use the fixtures, but first let's take a look at a sample unit test:
require "test_helper"
class WebSiteTest < ActiveSupport::TestCase
test "web_site_count" do
assert_equal 2, WebSite.count
end
end
By default, test_helper.rb
will load all of your fixtures into your test database, so this test will succeed.
The testing environment will automatically load all the fixtures into the database before each test. To ensure consistent data, the environment deletes the fixtures before running the load.
In addition to being available in the database, the fixture's data may also be accessed by using a special dynamic method, which has the same name as the model.
Passing in a fixture name to this dynamic method returns the fixture matching this name:
test "find one" do
assert_equal "Ruby on Rails", web_sites(:rubyonrails).name
end
Passing in multiple fixture names returns all fixtures matching these names:
test "find all by name" do
assert_equal 2, web_sites(:rubyonrails, :google).length
end
Passing in no arguments returns all fixtures:
test "find all" do
assert_equal 2, web_sites.length
end
Passing in any fixture name that does not exist will raise StandardError
:
test "find by name that does not exist" do
assert_raise(StandardError) { web_sites(:reddit) }
end
Alternatively, you may enable auto-instantiation of the fixture data. For instance, take the following tests:
test "find_alt_method_1" do
assert_equal "Ruby on Rails", @web_sites['rubyonrails']['name']
end
test "find_alt_method_2" do
assert_equal "Ruby on Rails", @rubyonrails.name
end
In order to use these methods to access fixtured data within your test cases, you must specify one of the following in your ActiveSupport::TestCase-derived class:
-
to fully enable instantiated fixtures (enable alternate methods #1 and #2 above)
self.use_instantiated_fixtures = true
-
create only the hash for the fixtures, do not 'find' each instance (enable alternate method #1 only)
self.use_instantiated_fixtures = :no_instances
Using either of these alternate methods incurs a performance hit, as the fixtured data must be fully traversed in the database to create the fixture hash and/or instance variables. This is expensive for large sets of fixtured data.
Dynamic fixtures with ERB
Sometimes you don't care about the content of the fixtures as much as you care about the volume. In these cases, you can mix ERB
in with your YAML fixtures to create a bunch of fixtures for load testing, like:
<% 1.upto(1000) do |i| %>
fix_<%= i %>:
id: <%= i %>
name: guy_<%= i %>
<% end %>
This will create 1000 very simple fixtures.
Using ERB
, you can also inject dynamic values into your fixtures with inserts like <%= Date.today.strftime("%Y-%m-%d") %>
. This is however a feature to be used with some caution. The point of fixtures are that they're stable units of predictable sample data. If you feel that you need to inject dynamic values, then perhaps you should reexamine whether your application is properly testable. Hence, dynamic values in fixtures are to be considered a code smell.
Helper methods defined in a fixture will not be available in other fixtures, to prevent against unwanted inter-test dependencies. Methods used by multiple fixtures should be defined in a module that is included in ActiveRecord::FixtureSet.context_class
.
-
define a helper method in
test_helper.rb
module FixtureFileHelpers def file_sha(path) OpenSSL::Digest::SHA256.hexdigest(File.read(Rails.root.join('test/fixtures', path))) end end ActiveRecord::FixtureSet.context_class.include FixtureFileHelpers
-
use the helper method in a fixture
photo: name: kitten.png sha: <%= file_sha 'files/kitten.png' %>
Transactional Tests
Test cases can use begin+rollback to isolate their changes to the database instead of having to delete+insert for every test case.
class FooTest < ActiveSupport::TestCase
self.use_transactional_tests = true
test "godzilla" do
assert_not_empty Foo.all
Foo.destroy_all
assert_empty Foo.all
end
test "godzilla aftermath" do
assert_not_empty Foo.all
end
end
If you preload your test database with all fixture data (probably by running bin/rails db:fixtures:load
) and use transactional tests, then you may omit all fixtures declarations in your test cases since all the data's already there and every case rolls back its changes.
In order to use instantiated fixtures with preloaded data, set self.pre_loaded_fixtures
to true. This will provide access to fixture data for every table that has been loaded through fixtures (depending on the value of use_instantiated_fixtures
).
When not to use transactional tests:
-
You're testing whether a transaction works correctly. Nested transactions don't commit until all parent transactions commit, particularly, the fixtures transaction which is begun in setup and rolled back in teardown. Thus, you won't be able to verify the results of your transaction until Active Record supports nested transactions or savepoints (in progress).
-
Your database does not support transactions. Every Active Record database supports transactions except MySQL MyISAM. Use InnoDB, MaxDB, or NDB instead.
Advanced Fixtures
Fixtures that don't specify an ID get some extra features:
-
Stable, autogenerated IDs
-
Label references for associations (belongs_to, has_one, has_many)
-
HABTM associations as inline lists
There are some more advanced features available even if the id is specified:
-
Autofilled timestamp columns
-
Fixture label interpolation
-
Support for YAML defaults
Stable, Autogenerated IDs
Here, have a monkey fixture:
george:
id: 1
name: George the Monkey
reginald:
id: 2
name: Reginald the Pirate
Each of these fixtures has two unique identifiers: one for the database and one for the humans. Why don't we generate the primary key instead? Hashing each fixture's label yields a consistent ID:
george: # generated id: 503576764
name: George the Monkey
reginald: # generated id: 324201669
name: Reginald the Pirate
Active Record looks at the fixture's model class, discovers the correct primary key, and generates it right before inserting the fixture into the database.
The generated ID for a given label is constant, so we can discover any fixture's ID without loading anything, as long as we know the label.
Label references for associations (belongs_to, has_one, has_many)
Specifying foreign keys in fixtures can be very fragile, not to mention difficult to read. Since Active Record can figure out the ID of any fixture from its label, you can specify FK's by label instead of ID.
belongs_to
Let's break out some more monkeys and pirates.
### in pirates.yml
reginald:
id: 1
name: Reginald the Pirate
monkey_id: 1
### in monkeys.yml
george:
id: 1
name: George the Monkey
pirate_id: 1
Add a few more monkeys and pirates and break this into multiple files, and it gets pretty hard to keep track of what's going on. Let's use labels instead of IDs:
### in pirates.yml
reginald:
name: Reginald the Pirate
monkey: george
### in monkeys.yml
george:
name: George the Monkey
pirate: reginald
Pow! All is made clear. Active Record reflects on the fixture's model class, finds all the belongs_to
associations, and allows you to specify a target label for the association (monkey: george) rather than a target id for the FK (monkey_id: 1
).
Polymorphic belongs_to
Supporting polymorphic relationships is a little bit more complicated, since Active Record needs to know what type your association is pointing at. Something like this should look familiar:
### in fruit.rb
belongs_to :eater, polymorphic: true
### in fruits.yml
apple:
id: 1
name: apple
eater_id: 1
eater_type: Monkey
Can we do better? You bet!
apple:
eater: george (Monkey)
Just provide the polymorphic target type and Active Record will take care of the rest.
has_and_belongs_to_many or has_many :through
Time
to give our monkey some fruit.
### in monkeys.yml
george:
id: 1
name: George the Monkey
### in fruits.yml
apple:
id: 1
name: apple
orange:
id: 2
name: orange
grape:
id: 3
name: grape
### in fruits_monkeys.yml
apple_george:
fruit_id: 1
monkey_id: 1
orange_george:
fruit_id: 2
monkey_id: 1
grape_george:
fruit_id: 3
monkey_id: 1
Let's make the HABTM fixture go away.
### in monkeys.yml
george:
id: 1
name: George the Monkey
fruits: apple, orange, grape
### in fruits.yml
apple:
name: apple
orange:
name: orange
grape:
name: grape
Zap! No more fruits_monkeys.yml file. We've specified the list of fruits on George's fixture, but we could've just as easily specified a list of monkeys on each fruit. As with belongs_to
, Active Record reflects on the fixture's model class and discovers the has_and_belongs_to_many
associations.
Autofilled Timestamp
Columns
If your table/model specifies any of Active Record's standard timestamp columns (created_at
, created_on
, updated_at
, updated_on
), they will automatically be set to Time.now
.
If you've set specific values, they'll be left alone.
Fixture label interpolation
The label of the current fixture is always available as a column value:
geeksomnia:
name: Geeksomnia's Account
subdomain: $LABEL
email: $LABEL@email.com
Also, sometimes (like when porting older join table fixtures) you'll need to be able to get a hold of the identifier for a given label. ERB
to the rescue:
george_reginald:
monkey_id: <%= ActiveRecord::FixtureSet.identify(:reginald) %>
pirate_id: <%= ActiveRecord::FixtureSet.identify(:george) %>
Support for YAML defaults
You can set and reuse defaults in your fixtures YAML file. This is the same technique used in the database.yml
file to specify defaults:
DEFAULTS: &DEFAULTS
created_on: <%= 3.weeks.ago.to_fs(:db) %>
first:
name: Smurf
<<: *DEFAULTS
second:
name: Fraggle
<<: *DEFAULTS
Any fixture labeled “DEFAULTS” is safely ignored.
Besides using “DEFAULTS”, you can also specify what fixtures will be ignored by setting “ignore” in “_fixture” section.
# users.yml
_fixture:
ignore:
- base
# or use "ignore: base" when there is only one fixture that needs to be ignored.
base: &base
admin: false
introduction: "This is a default description"
admin:
<<: *base
admin: true
visitor:
<<: *base
In the above example, 'base' will be ignored when creating fixtures. This can be used for common attributes inheriting.
Configure the fixture model class
It's possible to set the fixture's model class directly in the YAML file. This is helpful when fixtures are loaded outside tests and set_fixture_class
is not available (e.g. when running bin/rails db:fixtures:load
).
_fixture:
model_class: User
david:
name: David
Any fixtures labeled “_fixture” are safely ignored.
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Constants
MAX_ID | = | 2**30 - 1 |
Attributes
[R] | config | |
[R] | fixtures | |
[R] | ignored_fixtures | |
[R] | model_class | |
[R] | name | |
[R] | table_name |
Class Public methods
cache_fixtures(connection, fixtures_map) Link
cache_for_connection(connection) Link
cached_fixtures(connection, keys_to_fetch = nil) Link
create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base, &block) Link
# File activerecord/lib/active_record/fixtures.rb, line 555 def create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base, &block) fixture_set_names = Array(fixture_set_names).map(&:to_s) class_names = ClassCache.new class_names, config # FIXME: Apparently JK uses this. connection = block_given? ? block : lambda { ActiveRecord::Base.connection } fixture_files_to_read = fixture_set_names.reject do |fs_name| fixture_is_cached?(connection.call, fs_name) end if fixture_files_to_read.any? fixtures_map = read_and_insert( fixtures_directory, fixture_files_to_read, class_names, connection, ) cache_fixtures(connection.call, fixtures_map) end cached_fixtures(connection.call, fixture_set_names) end
fixture_is_cached?(connection, table_name) Link
identify(label, column_type = :integer) Link
Returns a consistent, platform-independent identifier for label
. Integer
identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
instantiate_all_loaded_fixtures(object, load_instances = true) Link
instantiate_fixtures(object, fixture_set, load_instances = true) Link
# File activerecord/lib/active_record/fixtures.rb, line 540 def instantiate_fixtures(object, fixture_set, load_instances = true) return unless load_instances fixture_set.each do |fixture_name, fixture| object.instance_variable_set "@#{fixture_name}", fixture.find rescue FixtureClassNotFound nil end end
new(_, name, class_name, path, config = ActiveRecord::Base) Link
# File activerecord/lib/active_record/fixtures.rb, line 650 def initialize(_, name, class_name, path, config = ActiveRecord::Base) @name = name @path = path @config = config self.model_class = class_name @fixtures = read_fixture_files(path) @table_name = model_class&.table_name || self.class.default_fixture_table_name(name, config) end
reset_cache() Link
Instance Public methods
[](x) Link
[]=(k, v) Link
each(&block) Link
size() Link
table_rows() Link
Returns a hash of rows to be inserted. The key is the table, the value is a list of rows to insert to that table.
# File activerecord/lib/active_record/fixtures.rb, line 680 def table_rows # allow specifying fixtures to be ignored by setting `ignore` in `_fixture` section fixtures.except!(*ignored_fixtures) TableRows.new( table_name, model_class: model_class, fixtures: fixtures, ).to_hash end