Fixtures in Rails Tests

Fixtures  are very much relevant in Rails testing. Fixtures are a way of organizing your test data.Testing the application helps to debug it more efficiently and ensures the desired functionality to the application. Let’s have a look on them. It is used to manage the test data. It tests against the real data and is written in YAML files. For each model in the application, there is a .yml file in the test/fixtures directory. When we generate the model using rails g it will automatically create the .yml file also. Here you can see an example,

 name: redpanthers
 message: hi
Here ‘Matz’ is the fixture name. And the name and message are the fields in the User model. Fixtures come in 3 flavours:
  • YAML fixtures: It is a file format which describes data structures in human-readable format.These are stored in a single file per model(above example is in yaml format).
  • CSV fixtures: Here values are kept in the Comma Separated Value (CSV) format. These are stored in a single file but instead end with the .csv file extension.


  name, message
   redpanthers, hi
  • Single-file fixtures: These are the original format for Active Record.


name => redpanthers
message => hi

Creating multiple/random items in fixtures

You can create multiple items as:
 name: redpanthers
 message: hi
 name: google
 message: hello
When you add fixtures, they get IDs based on a hash of the table name and the fixture name. To us humans, they just look like random numbers. So there is no need to define the id for this. It will ensure that the id is unique for every item. Fixtures are unordered. If you want ordered items, use the omap YAML type. Also, you can access the data in the test as:
test "find" do
  assert_equal "User", users(:Adorn).name
Where ‘users’ is the name of the yml file and ‘Adorn’ is the fixture name.

ERB Fixtures

You can add ERB with your YAML fixtures to create a bunch of fixtures as:
<% 1000.times do |i| %>
user_<%= i %>:
  name: <%= "user#{i}" %>
  message: <%= "message#{i}" %>
<% end %>
In the above example, the code generate 1000 users.

Writing belongs_to/has_many relationships

We can also define associations between fixtures. For example, if a user has so many customers there exists a has_many/belongs to a relationship. So we can get the value as:
# In fixtures/customers.yml
 name: Tiago
# In fixtures/users.yml
 name: redpanthers
 message: hi
 customer: Jacob
Like above, you can get customer details in users.yml.

Why are they Special?

  • It allows you to populate your test database with values so that you can test more conveniently without having to put lots of data into it when setting up a test run.
  • These are the instances of Active Record. So you can access the object directly because it is automatically setup as a local variable of the test case.


# this will return the User object for the fixture named David
  • We can set a value to nil/blank from the fixture.


require 'yaml'
YAML.load "--- \n:private: null\n")
=> {:private=>nil}
# In fixture
 name: john
 private: null
I hope this article helps you in a better way to know the basics about fixtures!