Minitest basics (assert style) in Ruby - Step-by-Step Execution

Concept Flow - Minitest basics (assert style)

Write test method

↓

Call assert method

↓

Evaluate condition

↓

Pass

↓

Report result

↓

Next test or end

Tests run by calling assert methods that check conditions; if true, test passes, else it fails and reports.

Execution Sample

Ruby

require 'minitest/autorun'

class TestExample < Minitest::Test
  def test_sum
    assert_equal 4, 2 + 2
  end
end

This code defines a test that checks if 2 + 2 equals 4 using assert_equal.

Execution Table

Step	Action	Evaluation	Result
1	Run test_sum method	assert_equal 4, 2 + 2	Check if 4 == 4
2	Evaluate condition	4 == 4	True
3	Test result	Pass	No error raised
4	Report	Test passed	Output success message
5	End	All tests done	Exit

💡 Test ends after all assertions pass or fail; here assertion is true so test passes.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
expected	4	4	4	4
actual	undefined	2 + 2	4	4
assertion_result	undefined	undefined	true	true

Key Moments - 3 Insights

Why does the test pass even though we don't see any output?

Because assert_equal passes silently when the condition is true, as shown in execution_table step 3 and 4.

What happens if the assertion fails?

If the assertion fails, Minitest raises an error and reports failure immediately, unlike the pass case in execution_table.

Why do we use assert_equal instead of just comparing values?

assert_equal provides clear pass/fail reporting and integrates with Minitest framework, as shown in the flow from calling assert to reporting.

Visual Quiz - 3 Questions

Look at the execution_table, what is the evaluation result at Step 2?

A Error

B False

C True

D Undefined

💡 Hint

Check the 'Evaluation' and 'Result' columns at Step 2 in execution_table.

At which step does the test report success?

A Step 4

B Step 3

C Step 1

D Step 5

💡 Hint

Look for the step where 'Test passed' is mentioned in execution_table.

If the assertion was false, what would change in the execution_table?

A Step 1 would be skipped

B Step 2 evaluation would be False and Step 3 would show failure

C Step 5 would report success

D No changes, test always passes

💡 Hint

Refer to key_moments about assertion failure and execution_table step 2 and 3.

Concept Snapshot

Minitest uses assert methods to check conditions.
assert_equal(expected, actual) tests equality.
If true, test passes silently.
If false, test fails with error.
Tests are methods inside classes inheriting from Minitest::Test.
Run tests with 'ruby filename.rb'.

Full Transcript

This visual trace shows how a Minitest assert style test runs. First, the test method is called. Then the assert_equal method compares expected and actual values. If they match, the assertion passes silently and the test reports success. If they don't match, Minitest raises an error and reports failure. Variables like expected and actual hold values during the test. The key moments explain why tests pass silently and what happens on failure. The quiz checks understanding of evaluation results and reporting steps. This helps beginners see how Minitest checks conditions step-by-step.

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