RSpec expectations and matchers in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this RSpec expectation?

Consider the following RSpec test snippet. What will be the result when it runs?

Ruby

describe 'Array' do
  it 'checks if array includes 3' do
    expect([1, 2, 3, 4]).to include(3)
  end
end

A The test passes because 3 is included in the array.

B The test fails because include matcher only works with strings.

C The test raises a SyntaxError due to missing parentheses.

D The test fails because the array does not include 3.

💡 Hint

The include matcher checks if the given element is present in the collection.

The include matcher in RSpec checks if the expected element is present in the array. Since 3 is in [1, 2, 3, 4], the test passes.

❓ Predict Output

intermediate

What error does this RSpec expectation raise?

What error will this RSpec test produce when run?

Ruby

describe 'String' do
  it 'checks string length' do
    expect('hello').to have_length(5)
  end
end

A No error, test passes because 'hello' length is 5.

B SyntaxError due to incorrect matcher syntax.

C NoMethodError because have_length matcher does not exist.

D Test fails with expectation failure because length is not 5.

💡 Hint

Check if have_length is a valid RSpec matcher.

RSpec does not have a built-in matcher called have_length. The correct matcher is have_attributes(length: 5) or use expect(string.length).to eq(5).

🧠 Conceptual

advanced

Which matcher correctly tests for raising an error?

You want to test that a method call raises a ZeroDivisionError. Which RSpec expectation is correct?

A expect(1 / 0).to raise_error(ZeroDivisionError)

B expect { 1 / 0 }.to raise_error(ZeroDivisionError)

C expect { 1 / 0 }.to raise_exception('ZeroDivisionError')

D expect(1 / 0).to raise_exception(ZeroDivisionError)

💡 Hint

Use a block with expect to test for errors.

To test for errors in RSpec, you must pass a block to expect. Options B and D call the expression immediately, causing the error before expect runs. Option B uses a wrong matcher name.

❓ Predict Output

advanced

What is the value of variable 'result' after this RSpec test?

Given this RSpec test, what will be the value of 'result' after it runs?

Ruby

result = nil
RSpec.describe 'Test' do
  it 'sets result' do
    result = 10
    expect(result).to eq(10)
  end
end

A result is nil

B result is 10

C result is undefined and raises NameError

D result is 0

💡 Hint

Consider variable scope inside RSpec blocks.

The 'result' inside the it block is a different local variable than the one outside. The outer 'result' remains nil after the test runs.

🔧 Debug

expert

Why does this RSpec test fail unexpectedly?

This test is supposed to check if an array is empty, but it fails. Why?

Ruby

describe 'Array' do
  it 'is empty' do
    arr = []
    expect(arr.empty?).to be true
  end
end

A The test fails because 'be true' matcher is deprecated and should be replaced with 'be_truthy'.

B The test fails because 'arr.empty?' returns false for an empty array.

C The test fails because 'expect' requires a block when testing boolean values.

D The matcher 'be true' expects the exact object 'true', but arr.empty? returns a boolean value, causing failure.

💡 Hint

Check the difference between 'be true' and 'be_truthy' matchers.

'be true' matcher expects the exact object true (i.e., object identity). arr.empty? returns true (boolean), so it should pass. However, in some Ruby versions or RSpec configurations, subtle differences cause failures. The recommended matcher is 'be_truthy' which checks truthiness instead of object identity.