Test-driven development workflow in Ruby

Introduction

Test-driven development helps you write code that works right from the start. It makes sure your program does what you want by testing it first.

When you want to build a small feature and be sure it works before adding more.

When fixing bugs to make sure the problem is solved and does not come back.

When learning a new programming concept and want to check your understanding.

When working in a team to keep code reliable and avoid breaking others' work.

When improving old code safely by testing changes step-by-step.

Syntax

Ruby

# 1. Write a test that fails
# 2. Write just enough code to pass the test
# 3. Run tests and see them pass
# 4. Refactor code to improve it
# 5. Repeat for next feature or fix

The test is written before the actual code.

Tests guide the coding process and catch mistakes early.

Examples

This is a simple test that checks if 2 + 3 equals 5.

Ruby

require 'minitest/autorun'

class TestCalculator < Minitest::Test
  def test_addition
    assert_equal 5, 2 + 3
  end
end

This is the code written to pass the test above.

Ruby

class Calculator
  def add(a, b)
    a + b
  end
end

Test updated to use the Calculator class method.

Ruby

require 'minitest/autorun'

class TestCalculator < Minitest::Test
  def test_addition
    calc = Calculator.new
    assert_equal 5, calc.add(2, 3)
  end
end

Sample Program

This program shows the full test-driven workflow: first the test checks addition, then the Calculator class is created with the add method to pass the test.

Ruby

require 'minitest/autorun'

class Calculator
  def add(a, b)
    a + b
  end
end

class TestCalculator < Minitest::Test
  def test_addition
    calc = Calculator.new
    assert_equal 5, calc.add(2, 3)
  end
end

Important Notes

Always start by writing a test that fails to know what you want your code to do.

Keep tests small and focused on one thing at a time.

Refactor your code after tests pass to keep it clean and simple.

Summary

Write tests before code to guide development.

Run tests often to catch errors early.

Refactor code safely with tests as a safety net.

Practice

1. In Ruby's test-driven development (TDD) workflow, what is the first step you should do?

easy

A. Run all tests to check for errors

B. Write a failing test that defines the desired behavior

C. Refactor the existing code

D. Write the full implementation code

Solution

1. Step 1: Understand the TDD cycle

   The TDD cycle starts by writing a test that fails because the feature is not implemented yet.

2. Step 2: Identify the first action in TDD

   Writing a failing test first guides the development and ensures the code meets requirements.

3. Final Answer:

   Write a failing test that defines the desired behavior -> Option B

4. Quick Check:

   First step in TDD = Write failing test [OK]

Hint: Remember: Test first, code second in TDD [OK]

Common Mistakes:

• Starting by writing implementation code before tests
• Refactoring before any test is written
• Running tests before any code or test exists

2. Which Ruby command runs all tests in a typical TDD workflow using Minitest?

easy

A. rails server

B. rspec test_file.rb

C. ruby test_file.rb

D. bundle install

Solution

1. Step 1: Identify the test framework command

   Minitest tests are run by executing the Ruby test file directly with ruby test_file.rb.

2. Step 2: Eliminate unrelated commands

   rspec is for RSpec tests, rails server starts the server, and bundle install installs gems.

3. Final Answer:

   ruby test_file.rb -> Option C

4. Quick Check:

   Run Minitest with ruby test_file.rb [OK]

Hint: Run tests by executing test files with ruby [OK]

Common Mistakes:

• Using rspec command for Minitest tests
• Confusing server start with test run
• Running bundle install instead of tests

3. Given this Ruby test and code, what will be the test output?

require 'minitest/autorun'

class Calculator
  def add(a, b)
    a + b
  end
end

class TestCalculator < Minitest::Test
  def test_add
    calc = Calculator.new
    assert_equal 5, calc.add(2, 3)
  end
end

medium

A. 1 test, 0 failures

B. 1 test, 1 failure

C. SyntaxError

D. No tests run

Solution

1. Step 1: Analyze the test and method

   The add method returns the sum of two numbers. The test expects 5 from adding 2 and 3.

2. Step 2: Check if test passes

   Since 2 + 3 equals 5, the assertion passes and the test succeeds.

3. Final Answer:

   1 test, 0 failures -> Option A

4. Quick Check:

   Correct sum = test passes [OK]

Hint: If method matches test expectation, test passes [OK]

Common Mistakes:

• Thinking test fails when it actually passes
• Confusing syntax error with test failure
• Ignoring the assert_equal expected value

4. What is wrong with this TDD workflow snippet in Ruby?

class TestCalculator < Minitest::Test
  def test_multiply
    calc = Calculator.new
    assert_equal 6, calc.multiply(2, 3)
  end
end

class Calculator
  def multiply(a, b)
    a - b
  end
end

medium

A. The test method name is incorrect

B. assert_equal arguments are reversed

C. Calculator class is missing

D. The multiply method subtracts instead of multiplies

Solution

1. Step 1: Compare method implementation with test expectation

   The test expects multiply(2, 3) to return 6, but the method subtracts a - b.

2. Step 2: Identify the error cause

   Subtracting 2 - 3 gives -1, which will fail the test expecting 6.

3. Final Answer:

   The multiply method subtracts instead of multiplies -> Option D

4. Quick Check:

   Method logic must match test expectation [OK]

Hint: Check method logic matches test assertions [OK]

Common Mistakes:

• Confusing subtraction with multiplication
• Ignoring method implementation details
• Assuming test method name affects test result

5. You want to safely improve your Ruby code after passing tests. Which TDD step lets you do this without breaking functionality?

hard

A. Refactor the code while running tests frequently

B. Write new tests before changing code

C. Run tests only after all changes are done

D. Delete old tests to simplify code

Solution

1. Step 1: Understand the role of refactoring in TDD

   Refactoring means improving code structure without changing behavior, done safely with tests as a safety net.

2. Step 2: Identify the correct practice

   Running tests frequently during refactoring ensures no functionality breaks.

3. Final Answer:

   Refactor the code while running tests frequently -> Option A

4. Quick Check:

   Refactor + frequent tests = safe improvements [OK]

Hint: Refactor with tests running often to catch errors [OK]

Common Mistakes:

• Running tests only after all changes
• Deleting tests which protect code quality
• Writing tests after refactoring instead of before