Minitest basics (assert style) in Ruby

Introduction

Minitest helps you check if your Ruby code works correctly by running small tests. Using assert style means you write simple true/false checks.

When you want to make sure a method returns the right result.

When you want to catch mistakes early by testing small parts of your code.

When you want to automatically check your code after changes.

When you want to learn how to write tests in Ruby easily.

Syntax

Ruby

require 'minitest/autorun'

class TestExample < Minitest::Test
  def test_something
    assert condition, 'optional failure message'
  end
end

assert checks if the condition is true.

If the condition is false, the test fails and shows the message.

Examples

Checks if 5 is greater than 3, which is true, so test passes.

Ruby

assert 5 > 3

Checks if the string 'hello' contains 'h'.

Ruby

assert 'hello'.include?('h')

This test will fail and show 'Math is broken!' because 2 + 2 is not 5.

Ruby

assert 2 + 2 == 5, 'Math is broken!'

Sample Program

This program has three tests. Two will pass because the math is correct. One will fail to show how Minitest reports errors.

Ruby

require 'minitest/autorun'

class TestMath < Minitest::Test
  def test_addition
    assert 2 + 2 == 4, 'Addition should work'
  end

  def test_subtraction
    assert 5 - 3 == 2
  end

  def test_fail_example
    assert 1 == 0, 'This test will fail'
  end
end

Important Notes

Use assert for simple true/false checks.

For checking equality, you can also use assert_equal expected, actual for clearer messages.

Run your tests from the command line with ruby your_test_file.rb.

Summary

Minitest assert style lets you write simple tests that check if conditions are true.

Tests help catch mistakes early and keep your code working well.

Use clear messages to understand why a test fails.

Practice

1. What does the assert method in Minitest do?

easy

A. Checks if a condition is true and fails the test if not

B. Runs the entire test suite automatically

C. Prints the test results to the console

D. Defines a new test case class

Solution

1. Step 1: Understand the purpose of assert

   The assert method is used to verify that a condition is true during a test.

2. Step 2: What happens if the condition is false?

   If the condition is false, the test fails and reports an error.

3. Final Answer:

   Checks if a condition is true and fails the test if not -> Option A

4. Quick Check:

   assert checks truth = B [OK]

Hint: Assert checks if condition is true, else test fails [OK]

Common Mistakes:

• Thinking assert runs all tests
• Confusing assert with printing output
• Believing assert defines test classes

2. Which of the following is the correct syntax to write a test method in Minitest using assert style?

easy

A. function test_example() { assert_equal(5, 2 + 3); }

B. def test_example; assert_equal 5, 2 + 3; end

C. test 'example' do; assert_equal 5, 2 + 3; end

D. test_example() { assert_equal 5, 2 + 3 }

Solution

1. Step 1: Identify Ruby method syntax for Minitest

   In Minitest, test methods start with def test_... and end with end.

2. Step 2: Check the assert usage inside the method

   assert_equal expected, actual is used correctly inside the method.

3. Final Answer:

   def test_example; assert_equal 5, 2 + 3; end -> Option B

4. Quick Check:

   Ruby test method syntax = C [OK]

Hint: Test methods start with def test_ and end with end [OK]

Common Mistakes:

• Using non-Ruby syntax like function or braces
• Using test do blocks which belong to other frameworks
• Missing def or end keywords

3. What will be the output when running this Minitest code?

require 'minitest/autorun'

class SampleTest < Minitest::Test
  def test_sum
    assert_equal 10, 5 + 5
  end

  def test_fail
    assert 3 > 5, '3 is not greater than 5'
  end
end

medium

A. One test passes, one test fails with message '3 is not greater than 5'

B. Both tests pass successfully

C. Syntax error due to incorrect assert usage

D. Both tests fail without any message

Solution

1. Step 1: Analyze test_sum method

   assert_equal 10, 5 + 5 checks if 10 equals 10, which is true, so this test passes.

2. Step 2: Analyze test_fail method

   assert 3 > 5 checks if 3 is greater than 5, which is false, so this test fails and shows the message '3 is not greater than 5'.

3. Final Answer:

   One test passes, one test fails with message '3 is not greater than 5' -> Option A

4. Quick Check:

   assert_equal true, assert false with message = D [OK]

Hint: Check each assert condition true or false to predict pass/fail [OK]

Common Mistakes:

• Assuming both tests pass
• Confusing assert and assert_equal behavior
• Ignoring failure message in assert

4. Identify the error in this Minitest code snippet:

class MyTest < Minitest::Test
  def test_check
    assert_equal(4, 2 + 2
  end
end

medium

A. Test method name does not start with 'test_'

B. Incorrect class inheritance from Minitest::Test

C. Missing closing parenthesis in assert_equal call

D. assert_equal arguments are in wrong order

Solution

1. Step 1: Check syntax of assert_equal call

   The line assert_equal(4, 2 + 2 is missing a closing parenthesis.

2. Step 2: Verify other parts of the code

   Class inheritance and method name are correct, and argument order is correct (expected, actual).

3. Final Answer:

   Missing closing parenthesis in assert_equal call -> Option C

4. Quick Check:

   Syntax errors often from missing parentheses = A [OK]

Hint: Count parentheses carefully in assert calls [OK]

Common Mistakes:

• Ignoring missing parentheses causing syntax errors
• Thinking test method name can be arbitrary
• Confusing argument order in assert_equal

5. You want to write a Minitest that checks if a method greet(name) returns 'Hello, name!'. Which assert statement correctly tests this behavior?

hard

A. assert greet('Alice') = 'Hello, Alice!'

B. assert 'Hello, Alice!', greet('Alice')

C. assert_equal greet('Alice'), 'Hello Alice!'

D. assert_equal 'Hello, Alice!', greet('Alice')

Solution

1. Step 1: Understand assert_equal argument order

   The first argument is the expected value, the second is the actual result from the method.

2. Step 2: Check each option's argument order and syntax

   assert_equal 'Hello, Alice!', greet('Alice') correctly uses expected first, actual second. assert 'Hello, Alice!', greet('Alice') asserts a truthy string (always passes), ignoring actual result. assert_equal greet('Alice'), 'Hello Alice!' reverses order and uses wrong expected (missing comma). assert greet('Alice') = 'Hello, Alice!' uses assignment (=), syntax error.

3. Final Answer:

   assert_equal 'Hello, Alice!', greet('Alice') -> Option D

4. Quick Check:

   Expected first, actual second in assert_equal = A [OK]

Hint: assert_equal expects expected value first, actual second [OK]

Common Mistakes:

• Swapping expected and actual arguments
• Using assignment (=) instead of comparison (==)
• Using assert with assignment causing syntax error