Model tests in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Rails model test?

Given the following RSpec test for a Rails model, what will be the test result?

Ruby on Rails

RSpec.describe User, type: :model do
  it "is invalid without an email" do
    user = User.new(email: nil)
    expect(user).not_to be_valid
  end
end

A The test raises a NoMethodError due to missing 'be_valid' matcher.

B The test fails because the User model does not validate email presence.

C The test passes because the User model requires an email.

D The test is skipped because no subject is defined.

💡 Hint

Check if the User model has a validation for email presence.

The test expects the user to be invalid without an email. If the User model validates presence of email, the test passes.

❓ state_output

intermediate

What is the value of errors after validation fails?

Consider this Rails model test snippet. What will be the content of user.errors[:email] after validation?

Ruby on Rails

user = User.new(email: nil)
user.valid?
user.errors[:email]

A [] (empty array)

B ["can't be blank"]

C ["is invalid"]

D nil

💡 Hint

What error message does Rails add for missing required fields?

When a presence validation fails, Rails adds "can't be blank" to the errors for that attribute.

📝 Syntax

advanced

Which option correctly tests uniqueness validation in Rails model?

You want to test that the User model validates uniqueness of email. Which RSpec test code is correct?

A it { should validate_uniqueness_of(:email) }

B it { should validate_uniqueness_of_email }

C it { expect(User).to validate_uniqueness_of(:email) }

D it { should validate_uniqueness(:email) }

💡 Hint

Check the syntax of the shoulda-matchers gem for uniqueness validation.

The correct syntax uses 'validate_uniqueness_of' matcher with should.

🔧 Debug

advanced

Why does this model test raise an error?

This test raises an error when run. What is the cause?

Ruby on Rails

RSpec.describe User, type: :model do
  it "validates presence of email" do
    user = User.new
    expect(user.valid?).to be_falsey
  end
end

A The test raises an error because the User model lacks any validations.

B The test raises an error because 'valid?' returns nil instead of boolean.

C The test raises an error because 'be_falsey' is not a valid matcher.

D The test does not raise an error; it runs and fails or passes depending on validations.

💡 Hint

Check if 'be_falsey' is a valid RSpec matcher and what 'valid?' returns.

'be_falsey' is a valid matcher and 'valid?' returns true or false. The test runs without error.

🧠 Conceptual

expert

What is the purpose of 'subject' in Rails model tests?

In RSpec model tests, what does defining 'subject { described_class.new }' achieve?

A It defines the default object for test examples, simplifying test code.

B It automatically runs validations before each test example.

C It sets the database schema for the model during tests.

D It mocks the model to avoid database calls during tests.

💡 Hint

Think about how 'subject' is used in RSpec to refer to the main object under test.

'subject' defines the main object tested, so you can write cleaner tests without repeating code.