Model tests in Ruby on Rails - Mini Project: Build & Apply

Model tests

📖 Scenario: You are building a simple Rails app to manage books in a library. Each book has a title and an author. You want to make sure your model works correctly by writing tests.

🎯 Goal: Write model tests for the Book model to check that it validates presence of title and author.

📋 What You'll Learn

Create a Book model with title and author attributes

Add presence validations for title and author

Write model tests to check these validations using RSpec

💡 Why This Matters

🌍 Real World

Model tests help ensure your data rules work correctly before saving to the database, preventing bad data and bugs.

💼 Career

Writing model tests is a key skill for Rails developers to maintain reliable and maintainable applications.

1

Create the Book model with attributes

Create a Rails model called Book with string attributes title and author using a migration.

Ruby on Rails

# Generate the Book model with title and author attributes
# Your code here

Hint

Use rails generate model Book title:string author:string to create the model and migration.

2

Add presence validations to Book model

In the Book model, add presence validations for the title and author attributes using validates :title, presence: true and validates :author, presence: true.

Ruby on Rails

class Book < ApplicationRecord
  # Add presence validations for title and author
  # Your code here
end

Hint

Use validates :attribute, presence: true for each attribute.

3

Create RSpec model test file for Book

Create a new RSpec test file spec/models/book_spec.rb with a describe Book block to hold your model tests.

Ruby on Rails

# Create spec/models/book_spec.rb
# Add describe block for Book model
# Your code here

Hint

Use describe Book, type: :model do ... end to start the test file.

4

Write presence validation tests for Book model

Inside the describe Book block, write two tests using it blocks to check that title and author must be present. Use should validate_presence_of(:title) and should validate_presence_of(:author) matchers.

Ruby on Rails

describe Book, type: :model do
  # Add tests for presence validations of title and author
  # Your code here
end

Hint

Use it { should validate_presence_of(:attribute) } syntax from shoulda-matchers gem.

Practice

1. What is the main purpose of model tests in a Rails application?

easy

A. To check data validations and model methods work correctly

B. To test the user interface layout

C. To verify database server performance

D. To check network connectivity

Solution

1. Step 1: Understand what model tests cover

   Model tests focus on the data layer, ensuring validations and methods behave as expected.

2. Step 2: Differentiate from other test types

   User interface and network tests are handled by other test types, not model tests.

3. Final Answer:

   To check data validations and model methods work correctly -> Option A

4. Quick Check:

   Model tests = data rules and logic [OK]

Hint: Model tests check data rules and methods only [OK]

Common Mistakes:

• Confusing model tests with UI tests
• Thinking model tests check server or network
• Assuming model tests check database performance

2. Which of the following is the correct syntax to test a presence validation on a Rails model attribute name using RSpec?

easy

A. expect(user).to validate_presence(:name)

B. expect(user).to be_validates_presence_of(:name)

C. expect(user).to have_presence_validation(:name)

D. expect(user).to validate_presence_of(:name)

Solution

1. Step 1: Recall RSpec validation matcher syntax

   The correct matcher is validate_presence_of(:attribute) used with expect(model).

2. Step 2: Check each option for exact syntax

   Only expect(user).to validate_presence_of(:name) matches the correct RSpec syntax for presence validation.

3. Final Answer:

   expect(user).to validate_presence_of(:name) -> Option D

4. Quick Check:

   RSpec presence validation = validate_presence_of [OK]

Hint: Use validate_presence_of matcher exactly in RSpec [OK]

Common Mistakes:

• Using incorrect matcher names
• Adding extra words like 'be_' or 'have_'
• Missing the '_of' suffix in matcher

3. Given this model test snippet:

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

What will this test check?

medium

A. That a User with an email is invalid

B. That the User model has a method called email

C. That a User without an email is invalid

D. That the User model saves successfully without email

Solution

1. Step 1: Analyze the test setup

   The test creates a User with email: nil, meaning no email is given.

2. Step 2: Understand the expectation

   The test expects user to NOT be valid, so it checks that missing email makes the user invalid.

3. Final Answer:

   That a User without an email is invalid -> Option C

4. Quick Check:

   Missing email -> invalid user [OK]

Hint: Check what attribute is nil and expected validity [OK]

Common Mistakes:

• Misreading the test as checking presence of method
• Thinking it tests saving instead of validation
• Confusing valid and invalid expectations

4. You wrote this model test:

it 'validates presence of title' do
  post = Post.new(title: '')
  expect(post).to be_valid
end

Why does this test fail?

medium

A. Because title is empty but test expects valid

B. Because Post.new requires a title argument

C. Because be_valid is not a valid matcher

D. Because the test is missing a database save

Solution

1. Step 1: Understand the test setup

   The test creates a Post with an empty string for title.

2. Step 2: Check the expectation vs validation

   If the model validates presence of title, empty string is invalid, but test expects valid, causing failure.

3. Final Answer:

   Because title is empty but test expects valid -> Option A

4. Quick Check:

   Empty title ≠ valid if presence validated [OK]

Hint: Empty string fails presence validation, expect invalid [OK]

Common Mistakes:

• Assuming empty string counts as present
• Thinking be_valid matcher is wrong
• Ignoring validation rules in test

5. You want to test a custom method full_name in your User model that combines first_name and last_name. Which is the best way to write this model test?

hard

A. Write a controller test that calls full_name

B. Create a User with first and last names, then expect user.full_name to equal their combination

C. Check that full_name is validated for presence

D. Test that full_name is a database column

Solution

1. Step 1: Identify what to test for a custom method

   Custom methods should be tested by calling them and checking their return values.

2. Step 2: Choose the test that verifies method output

   Creating a User with names and expecting full_name to return combined string is correct.

3. Final Answer:

   Create a User with first and last names, then expect user.full_name to equal their combination -> Option B

4. Quick Check:

   Test method output by calling it with sample data [OK]

Hint: Test method output by calling it on sample model instance [OK]

Common Mistakes:

• Testing method as if it were a database column
• Confusing validation tests with method tests
• Writing controller tests instead of model tests