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Custom RSpec matchers for ActiveRecord record creation


Add this line to your application's Gemfile:

gem 'active_record_block_matchers'

And then execute:

$ bundle

Or install it yourself as:

$ gem install active_record_block_matchers

Quick Examples

expect {
  post :create, user: { username: "bob", password: "BlueSteel45" }
}.to create_a(User)
  .with_attributes(username: "bob")
  .which {|bob| expect(AuthLibrary.authenticate("bob", "BlueSteel45")).to eq bob }

expect {
  post :create, user: { username: "bob", password: "BlueSteel45" }
}.to create(User => 1, Profile => 1)
    User => [{username: "bob"}],
    Profile => [{avatar_url: Avatar.default_avatar_url}],
  ).which { |new_records_hash|
    new_user = new_records_hash[User].first
    new_profile = new_records_hash[Profile].first
    expect(new_user.profile).to eq new_profile

Detailed Examples


aliases: create_an, create_a_new


expect { User.create! }.to create_a(User)

This can be very useful for controller tests:

expect { post :create, user: user_params }.to create_a(User)

You can chain .with_attributes as well to define a list of values you expect the new object to have. This works with both database attributes and computed values.

expect { User.create!(username: "bob") }
  .to create_a(User)
  .with_attributes(username: "bob")

This is a great way to test ActiveReocrd hooks on your model. For example, if your User model downcases all usernames before saving them to the database, you can test it like this:

expect { User.create!(username: "BOB") }
  .to create_a(User)
  .with_attributes(username: "bob")

You can even use RSpec's composable matchers:

expect { User.create!(username: "bob") }
  .to create_a(User)
  .with_attributes(username: a_string_starting_with("b"))

If you need to make assertions about things other than attribute equality, you can also chain .which with a block, and your block will receive the newly created record:

expect { User.create!(username: "BOB", password: "BlueSteel45") }
  .to create_a(User)
  .which { |user|
    expect(user.encrypted_password).to be_present
    expect(AuthLibrary.authenticate("bob", "BlueSteel45")).to eq user

Gotcha Warning: Be careful about your block syntax when chaining .which in your tests. If you write the above example with a do...end, the example will parse like this: expect {...}.to(create_a(User).which) do |user| ... end, so your block will not execute, and it may appear that your test is passing, when it is not.


aliases: create_records


expect { User.create!; User.create!; Profile.create! }
  .to create(User => 2, Profile => 1)

Just like the other matcher, you can chain with_attributes and which to assert about the particulars of the records:

expect { UserService.sign_up!(username: "bob", password: "BlueSteel45") }
  .to create(User => 1, Profile => 1)
    User => [{username: "bob"}],
    Profile => [{avatar_url: Avatar.default_avatar_url}]
  ).which { |records|
    # records is a hash with model classes for keys and the new records for values
    new_user = records[User].first
    new_profile = records[Profile].first
    expect(AuthLibrary.authenticate("bob", "BlueSteel45")).to eq new_user
    expect(new_user.profile).to eq new_profile

As noted, the which block yields a hash containing the new records whose counts were specified.

Order doesn't matter for the attributes specified in with_attributes, but you must provide an attribute hash for every record that was created. This means, if you expect the block to create, say 2 User records, you must provide an attributes hash for each new User record:

# This is correct:
expect { User.create!(username: "bob"); User.create!(username: "rhonda") }
  .to create(User => 2)
    User => [{username: "rhonda"}, {username: "bob"}]

# This will raise an error:
expect { User.create!(username: "bob"); User.create!(username: "rhonda") }
  .to create(User => 2)
    User => [{username: "rhonda"}]

# But this is totally fine if you really need a workaround:
# Just put the empty hashes last
expect { User.create!(username: "bob"); User.create!(username: "rhonda") }
  .to create(User => 2)
    User => [{username: "rhonda"}, {}]

Record Retrieval Strategies

There are currently two retrieval strategies implemented: :id and :timestamp. :id is the default, but this can be configured via the default_strategy configuration variable (more details below).

The ID and Timestamp Strategies work similarly. The ID Strategy queries the appropriate table(s) to find the highest ID value(s) before the block, then finds new records by looking for records with an ID that higher than that. The Timestamp Strategy uses Time.current to record the time before the block. Then it finds new records by looking for records that have a timestamp later than that.

The ID Strategy is the default because it doesn't rely on time values that may be imprecise or mocked out. The Timestamp Strategy is useful if your tables don't have autoincrementing integer primary keys.


You can configure the column names used by the ID or Timestamp Strategies. Put code like this in your spec_helper.rb or similar file:

ActiveRecordBlockMatchers.configure do |config|

  # default value is "id"
  config.id_column_name = "primary_key"

  # default value is "created_at"
  config.created_at_column_name = "created_timestamp"

  # default value is :id
  # must be one of [:id, :timestamp]
  config.default_strategy = :timestamp

You can also override the default strategy for individual assertions if needed:

expect { Person.create! }.to create_a(Person, strategy: :id)


After checking out the repo, run bin/setup to install dependencies. Then, run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.


  1. Fork it ([my-github-username]/active_record_block_matchers/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request


RSpec custom matchers for ActiveRecord








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